I am taking delivery of my new van next month. My previous van had an AGM battery and I used a C-Tek charger through the Anderson plug to trickle feed the battery when the van was laid up undercover. This worked a treat and kept the battery in good condition.
Do I need to trickle feed my lithium batteries when the van is in storage and there is no light to the panels. If so, what is the best way to do this. There seems to be conflicting advice on this on the net with some suggesting you do not trickle feed the batteries but monitor the charge and recharge when it reaches around 20%.
Thanks, MHJM
Whenarewethere said
02:50 PM Oct 27, 2022
Never under any circumstances. Lithium is basically the opposite of lead acid.
If in storage drain batteries to about 50% & leave them at that. Check in a year.
When charging while using make sure you use lithium setting. If not using for a few days drain batteries a bit. It is critical that when charged full that there is absolutely no further charging of any description. The opposite of lead acid.
If you do need a battery to run an alarm, ventilation fan or whatever while in storage. Use a lead acid battery & charge accordingly, it is just a lot easier... & less chance of an expensive stuff-up.
Whenarewethere said
02:54 PM Oct 27, 2022
This is a very long article, but be the time you finish reading it, you will be able to explain to others.
Depends on BMS ? I guess the trickle feed is more an issue when your not using anything as in storage ? Mine is always running the fridge ! I have a lithium
Charger now . The first 6 months I used the old AGM system .
Scubadoo said
08:11 PM Oct 27, 2022
I enjoy and read all the theories that abound on forums. Googxx links can be found to support all of them if you search enough. Believing is another story.
We have a 300Ah Sinolpoly 4 cell LiFePO4 battery that has now survived more than 8 years of full-time travelling abuse and at our last November annual c10 capacity test it can still deliver in excess of 4000Wh (c300Ah). Capacity is down less than 5% since new.
Our hands on daily use: My aim is to keep the battery full but it has also spent 8 years higher than that often mentioned plucked from the air 50% SOC without significant capacity degradation. It should be dead by now. Lowest ever from memory = 54%. Capacity at dawn is typically 75-80% SOC.
Even worse apart from a few experiments with an H02 active balancer years ago the cells have never been balanced since the original careful top balance nor has it ever proved necessary. Much, much worse according to another group of "experts" the cells should have self destructed long ago lying mounted on their sides for 8 years.
We must be lucky or perhaps the battery will only last 14 years and 10 months instead of its potential 15 years. At least I will never know.
All charging sources set to a 14.2V maximum. 75-80A alternator bulk forever once full while driving, up to 50A solar and the rare 30A mains charging. No absorption required. The battery is always 100% SOC at 14.2V regardless of charging current. Then maintain 13.3V (float in lead acid talk) that equates to around 98% SOC for our battery. Repeat next day. Victron BatteryProtect low voltage cut off is set at 12.1V. Never triggered.
The battery also starts our 3.9l turbo diesel engine often multiple times a day.
These batteries are apparently far more forgiving than many would have us believe.
-- Edited by Scubadoo on Thursday 27th of October 2022 08:15:05 PM
-- Edited by Scubadoo on Thursday 27th of October 2022 08:26:25 PM
Possum3 said
10:31 PM Oct 27, 2022
Welcome to GN's MHJM, I'm sure some of the electronics boffins in the forum will be able to help you sort out your new van.
TimTim said
12:16 AM Oct 28, 2022
Welcome MHJM,
As you can see by what Scubadoo has posted there is all sorts of conflicting theories in regards to LiFeOP4 and I have got to agree with him.
The idea of keeping the batteries at 50% when in storage is based upon maximising the cycles and life of the battery. Interestingly though you can read about compression of the cells to also maximise the life of the battery but in all the battery tear down videos that I have watched I have never once seen any compression applied.
So in answer to your question of whether you need to float or trickle charge your batteries the answer is no, but you may have to take a check on them periodically, and a bit more often than 12 months. The reason being is that some BMSs draw a parasitic current and I found this out after not being able to access my caravan for 4 months. When I eventually got access to my van both batteries had gone from being fully charged to just under 10.5v. Everything, else had been switched off but I had not disconnected the BMSs.
I have decided that Im not going to worry whether I get 3,000 or 4,000 cycles from them and whilst in storage I have mine fully charged but with my inverter left on and drawing 0.9A at 12v. This is easily replaced on most days by my solar panels.
If you drain your batteries down a bit and then monitor the voltage for a while you will get an idea of the rate of self discharge. You are not going to harm them but just be aware that LiFePO4 has a very flat discharge profile and that the voltage drops sharply at the end.
Good luck.
-- Edited by TimTim on Friday 28th of October 2022 12:17:56 AM
Tony Bev said
01:12 AM Oct 28, 2022
Welcome to the forum MHJM
I am not a techi, but I think a lot of confusion, comes from different manufactures of lithium battery/bms
I have lithium batteries from a mob called EVpower, which has the cell balancers on the battery, but a separate BMS (Battery Management System)
I am usually parked up for months at a time, and isolate the batteries at the BMS, and also isolate the solar panels from the DC/DC lithium profile charger
What I lose from the batteries, (if anything), is nothing to write home about
But, when I just isolated the solar panels, and 12 volt to the motorhome, I got parasitic current going to the BMS and DC/DC charger
This parasitic current ran down my batteries, in about 4/5 months
As already been said, I have not come across a manufacturer, who recommends to keep a lithium battery on a trickle charge
Dick0 said
11:34 AM Oct 28, 2022
I have an Isolator Switch for the positive (+) to and from batteries.
When van resting at home, before next adventure, batteries get a rest, also.
They are isolated at full charge (13.5V), and after several months there is no noticeable storage loss.
However, if batteries are feeding any appliance(s) during storage then have charger connected. The BMS will disconnect/connect input charge so the batteries will still cycle.
LiFePO4 batteries are easy to manage as the BMS(s) does most of the charging/storage management.
Mike Harding said
12:01 PM Oct 28, 2022
TimTim wrote:
some BMSs draw a parasitic current and I found this out after not being able to access my caravan for 4 months. When I eventually got access to my van both batteries had gone from being fully charged to just under 10.5v. Everything, else had been switched off but I had not disconnected the BMSs.
Are you sure it's the BMS? Under zero load conditions I would expect the BMS to go into sleep mode where its current draw should be in the micro or even nano amp region.
MHJM said
01:56 PM Oct 28, 2022
Thank you so much for your comments and advice. It is certainly very helpful.
This is a great forum to draw on the knowledge and experience of the community.
A newbie who appreciates the feedback!! Regards MHJM
-- Edited by MHJM on Friday 28th of October 2022 01:59:08 PM
Dick0 said
08:24 PM Oct 28, 2022
TimTim wrote:
Welcome MHJM,
As you can see by what Scubadoo has posted there is all sorts of conflicting theories in regards to LiFeOP4 and I have got to agree with him.
The idea of keeping the batteries at 50% when in storage is based upon maximising the cycles and life of the battery. Interestingly though you can read about compression of the cells to also maximise the life of the battery but in all the battery tear down videos that I have watched I have never once seen any compression applied.
So in answer to your question of whether you need to float or trickle charge your batteries the answer is no, but you may have to take a check on them periodically, and a bit more often than 12 months. The reason being is that some BMSs draw a parasitic current and I found this out after not being able to access my caravan for 4 months. When I eventually got access to my van both batteries had gone from being fully charged to just under 10.5v. Everything, else had been switched off but I had not disconnected the BMSs.
I have decided that Im not going to worry whether I get 3,000 or 4,000 cycles from them and whilst in storage I have mine fully charged but with my inverter left on and drawing 0.9A at 12v. This is easily replaced on most days by my solar panels.
If you drain your batteries down a bit and then monitor the voltage for a while you will get an idea of the rate of self discharge. You are not going to harm them but just be aware that LiFePO4 has a very flat discharge profile and that the voltage drops sharply at the end.
Good luck.
-- Edited by TimTim on Friday 28th of October 2022 12:17:56 AM
Surely the BMS would not be drawing any current, at rest or at any other time, but, the inverter drawing nearly 1.0A would draw down the battery(s) over time.
Tony Bev said
12:35 AM Oct 29, 2022
My Renogy DC/DC charger, with a separate Bluetooth module plugged in to it, plus the EVpower BMS, pulls power from the batteries, when the three of them are isolated from incoming and outgoing power
This parasitic current is too small for my el-cheapo clamp meter to measure
Even if this parasitic current is only 0.05 of an amp (50 milliamps), it would be 1.2 amps per day, or 8.4 amps each week, or around 33 amps each month
I do know that after somewhere between 4 to 5 months, when I went to check the batteries, the BMS had isolated itself from the battery at 10.5 volts
This meant that no more parasitic current went to the DC/DC charger and Bluetooth
From that time on, I have always isolated the batteries by switching the BMS off, and to the best of my knowledge, it completely stops any parasitic current
Mike Harding said
01:51 PM Oct 29, 2022
Tony Bev wrote:
Even if this parasitic current is only 0.05 of an amp (50 milliamps), it would be 1.2 amps per day, or 8.4 amps each week, or around 33 amps each month
50mA (0.05A) is a huge amount of standby current for a battery system (in most cases). A few years past I was involved in the design of the Holden Commodore VE instrument cluster and we had a standby current specification of 16uA or about 1/3000 of 50mA.
These days I would expect most electronic systems in sleep mode to use close to zero current although, depending on the system, they may need to wake up perhaps once a second to check for external events but, in most case that will add very little to energy consumption.
TimTim said
10:35 PM Oct 29, 2022
Mike Harding wrote:
TimTim wrote:
some BMSs draw a parasitic current and I found this out after not being able to access my caravan for 4 months. When I eventually got access to my van both batteries had gone from being fully charged to just under 10.5v. Everything, else had been switched off but I had not disconnected the BMSs.
Are you sure it's the BMS? Under zero load conditions I would expect the BMS to go into sleep mode where its current draw should be in the micro or even nano amp region.
Hi Mike,
I disconnected everything except the BMS on both batteries so did not expect any current draw. When I finally got back to my van the batteries were at different voltages and one was below the low voltage disconnect. It surprised me as my thoughts were similar to yours but then read on another forum where this has happened to a number of people. When i have some time I need to replicate and monitor what happens. I also need to test the high voltage and low voltage disconnects.
I took the batteries apart, did a top balance on the cells, and since then they been working flawlessly.
Mike Harding said
12:59 PM Oct 30, 2022
TimTim:
I can't recall what size batteries you own but, as an example, let's say 100Ah.
In 120 days they went from full charged to fully discharged say 90Ah.
90/120 = 750mA per day which is a considerable energy use for a battery system. Either the BMS is very poorly designed or something is wrong it seems to me.
A little Googling suggest a self-discharge rate of up to 5%/month for lithiums but there was one formal document (mainly behind a pay wall) which asserted that lithiums have a "memory" of being subject to excess temperature and will self discharge more in such a case. Dunno, but I am very surprised by your numbers... how do batteries waiting for sale in storage cope?
Interesting.
Tony Bev said
02:52 PM Oct 30, 2022
Hi Mike
I am not a techi, but there does appear to be some confusion, around parasitic current, with lithium batteries
I will try to explain in layman speak, why I think my parasitic current numbers was correct for my situation
Looking at the sketch below
When I isolate the incoming and the outgoing circuit breakers, I still have batteries feeding the BMS/DC-DC charger/Bluetooth as their lights are on Specs of the DC/DC charger are Snip below Self-consumption : 60mA
But when I just push the isolation button on the BMS then nothing goes to or from the battery, as no lights are showing And as far as I can tell, I lose nothing that I can measure from the battery
Hope that I have explained correctly
Mike Harding said
03:20 PM Oct 30, 2022
Hi Tony
It's hard to work out what is happening without more info. but it may be that some BMSs keep the Bluetooth, and other, systems active in order that consumers may check their battery's status. Consumers will like this but it will consume a fair bit of energy.
However I would expect that after a day or so when the BMS recognises the battery is in storage it would go into full sleep mode and minimise power consumption but perhaps it doesn't? This is really a design issue for individual BMSs.
Dunno :)
Dick0 said
11:18 AM Nov 1, 2022
Would like to know the answer even though it does not affect my Lithium system, but still good to know.
My batteries (3) have integrated BMS to balance and manage charging levels. No external BMS.
I don't have Bluetooth integrated with Charger or BMS.
I don't have a DC to DC charger (not required).
If you isolate batteries(s) input/output positives, and batteries deplete to 10.5V over a period of time, then I would think there is a major failure somewhere.
Dick0 said
11:23 AM Nov 1, 2022
TimTim wrote:
Mike Harding wrote:
TimTim wrote:
some BMSs draw a parasitic current and I found this out after not being able to access my caravan for 4 months. When I eventually got access to my van both batteries had gone from being fully charged to just under 10.5v. Everything, else had been switched off but I had not disconnected the BMSs.
Are you sure it's the BMS? Under zero load conditions I would expect the BMS to go into sleep mode where its current draw should be in the micro or even nano amp region.
Hi Mike,
I disconnected everything except the BMS on both batteries so did not expect any current draw. When I finally got back to my van the batteries were at different voltages and one was below the low voltage disconnect. It surprised me as my thoughts were similar to yours but then read on another forum where this has happened to a number of people. When i have some time I need to replicate and monitor what happens. I also need to test the high voltage and low voltage disconnects.
I took the batteries apart, did a top balance on the cells, and since then they been working flawlessly.
Also, the later (3 way) fridges with AES need to be connected to 12V or won't operate.
As do, some, brake-aways that trickle charge a utility backup battery.
Tony Bev said
05:53 PM Nov 1, 2022
Dick0 wrote:
Would like to know the answer even though it does not affect my Lithium system, but still good to know.
My batteries (3) have integrated BMS to balance and manage charging levels. No external BMS.
I don't have Bluetooth integrated with Charger or BMS.
I don't have a DC to DC charger (not required).
If you isolate batteries(s) input/output positives, and batteries deplete to 10.5V over a period of time, then I would think there is a major failure somewhere.
Hi Richard
If you are talking about my setup I think the reason for depleting batteries over a period of time, is probable different manufacturer of battery/bms/DC-DC chargers etc setups
When I mentioned that I isolated the incoming power, I only isolated the incoming solar cells/alternator power to the DC/DC charger When I mentioned that I isolated the outgoing power, I only isolated the outgoing power from the external BMS to the house circuit
I still had the batteries sending power to the external BMS, which in turn sent power to the DC/DC charger, which in turn sent power to the bluetooth adaptor, as each of them had lights showing
My system works slightly different than your, and I shall try and explain
EVPower batteries of four prismatic cells, have a cell balancer on each cell, with an external BMS capable of controlling all the cell balancers The idea of the cell balancer, as far as I am aware, is to balance the cells within a certain voltage, on both the charge and discharge cycle If/when any one cell is over or under by, I think it is half a volt, the BMS will close down to protect the battery If/when the incoming voltage is over 15 volt, or the battery is depleted to 10.5 volt, the BMS will close down to protect the battery
When I use the isolation button on the BMS to close the batteries down, then like your system, I have no power leaving the batteries or going to, the batteries
My DC/DC charger has both a alternator, and solar incoming connections, like your system I now only use the solar side of the DC/DC charger Much like a normal solar charger I find that 500 watt of roof solar, is more than adequate for my 12 volt requirements
I hope that I have explained it correctly
If not I will show you, if we meet up at Greens Lake (hopefully around January 2023)
Dick0 said
06:25 PM Nov 1, 2022
Tony Bev wrote:
Dick0 wrote:
Would like to know the answer even though it does not affect my Lithium system, but still good to know.
My batteries (3) have integrated BMS to balance and manage charging levels. No external BMS.
I don't have Bluetooth integrated with Charger or BMS.
I don't have a DC to DC charger (not required).
If you isolate batteries(s) input/output positives, and batteries deplete to 10.5V over a period of time, then I would think there is a major failure somewhere.
Hi Richard
If you are talking about my setup I think the reason for depleting batteries over a period of time, is probable different manufacturer of battery/bms/DC-DC chargers etc setups
When I mentioned that I isolated the incoming power, I only isolated the incoming solar cells/alternator power to the DC/DC charger When I mentioned that I isolated the outgoing power, I only isolated the outgoing power from the external BMS to the house circuit
I still had the batteries sending power to the external BMS, which in turn sent power to the DC/DC charger, which in turn sent power to the bluetooth adaptor, as each of them had lights showing
My system works slightly different than your, and I shall try and explain
EVPower batteries of four prismatic cells, have a cell balancer on each cell, with an external BMS capable of controlling all the cell balancers The idea of the cell balancer, as far as I am aware, is to balance the cells within a certain voltage, on both the charge and discharge cycle If/when any one cell is over or under by, I think it is half a volt, the BMS will close down to protect the battery If/when the incoming voltage is over 15 volt, or the battery is depleted to 10.5 volt, the BMS will close down to protect the battery
When I use the isolation button on the BMS to close the batteries down, then like your system, I have no power leaving the batteries or going to, the batteries
My DC/DC charger has both a alternator, and solar incoming connections, like your system I now only use the solar side of the DC/DC charger Much like a normal solar charger I find that 500 watt of roof solar, is more than adequate for my 12 volt requirements
I hope that I have explained it correctly
If not I will show you, if we meet up at Greens Lake (hopefully around January 2023)
Thanks for the clarification, Tony.
Would be great to catchup with you guys.
Noelpolar said
07:59 PM Nov 1, 2022
fwiw.... I have the same ev ppwer set up....the external bms has a 3 contact self latching contactor.... rated at 240amps (3 80amp parallel contacts)..... I conected my chargers erc to one of the 80 amp contacts and "unparalleled it"..... so.... 2 contacts carry up to 160amps and the 3rd connects the chargers..... I did this to ensure the solar charger etc was disconected when the battery was isolated etc.
Tony Bev said
11:12 PM Nov 1, 2022
Noelpolar wrote:
fwiw.... I have the same ev ppwer set up....the external bms has a 3 contact self latching contactor.... rated at 240amps (3 80amp parallel contacts)..... I conected my chargers erc to one of the 80 amp contacts and "unparalleled it"..... so.... 2 contacts carry up to 160amps and the 3rd connects the chargers..... I did this to ensure the solar charger etc was disconected when the battery was isolated etc.
Yes Neolpolar, that is how EVPower suggested I wire mine up, as I only have 2 batteries, and up to date I do not require any more battery power. So the third connection was available
I did ask the question why, as the fourth connection clearly says charger/load or something similar
It appears that the method behind the madness, is as you have already pointed out, with the external BMS isolated, either automatically or manually Nothing can go to or from the BMS, which means that nothing can go to or from the battery
Below is a pic with the protection cover, (which holds the manual isolation button), and buss bar of the external BMS removed, so others may understand a bit clearly
StormCamper said
03:15 AM Nov 26, 2022
Yeah there is only one logical reason to float/trickle LiFePo4 and that is it provides a cheap and convenient means of carrying the loads while free energy is still available. The thing most people miss by a country mile is you must float at a voltage under the 100% SoC resting voltage. You can float at 13.5, 13.2, 12.4 etc no problems. You can most likely float at 13.8v as long as the cumulative hours are rather small. The best thing you can possible do for long health is keep the battery at near full for as short a time as possible, so they thrive on being routinely cycled.
In storage always best to keep at 50% as a rule of thumb, once you go over 70% you will see the degradation long term. The whole point is to minimize side reactions which contribute to the build up of the oxide layers, this has been known for decades, anyone claiming otherwise doesn't have a clue.
I store mine at 35-40% to minimize any degradation, my bms has a noticable parasitic draw and so every 4 to 6months I need to top it back up to near 40%, technically 20% and stored in near fridge temps is best, this is true for most conventional li-ion cells, but LiFePo4 is a more robust, but for every guy who says "my cells are 9 years and doing great" there is another guy who complains his cells are just 7 years old and lost alot of capacity. Ultimately there are so many variables. I've seen cylindricals last 4 years until EOL 80%, yet others well north of 10. Some li-ion by themselves self discharge quite slow, some very slow. Again many factors like quality, luck, heat, SoC etc.
The reason dropins don't use compression is simple, cost, space and the fact it needs to be constantly baby sitted.
Scubadoo said
06:35 PM Nov 26, 2022
I would love to see some concrete evidence that constant high SOC equals significant capacity loss over time for LiFePO4 cells and some quantitative numbers.
Our now more than 8 years old Sinopoly 4 cell 300Ah battery has dropped in capacity in Ah from the original 315 to a mere 301 at our last annual November annual C/10 capacity test earlier this month.
The battery has never been "stored". It is used daily and has spent perhaps 95% of its near nine year life at >70% SOC. 100% each day end and c70% each daybreak.
As mentioned in an earlier post if the battery life in fact been shortened I will never know or really care.
Now if a scientist with actual practical experience, not doomsday theorist, proved otherwise ...
We are not too concerned. We have had our money's worth already.
TimTim said
09:51 PM Nov 26, 2022
Im with you Scubadoo. I keep my batteries fully charged and although I started out compressing the cells I decided to take it off and just bind them together with Gorilla tape. Whether I get 3000 instead of 4000 cycles I couldnt really care.
I am taking delivery of my new van next month. My previous van had an AGM battery and I used a C-Tek charger through the Anderson plug to trickle feed the battery when the van was laid up undercover. This worked a treat and kept the battery in good condition.
Do I need to trickle feed my lithium batteries when the van is in storage and there is no light to the panels. If so, what is the best way to do this. There seems to be conflicting advice on this on the net with some suggesting you do not trickle feed the batteries but monitor the charge and recharge when it reaches around 20%.
Thanks, MHJM
Never under any circumstances. Lithium is basically the opposite of lead acid.
If in storage drain batteries to about 50% & leave them at that. Check in a year.
When charging while using make sure you use lithium setting. If not using for a few days drain batteries a bit. It is critical that when charged full that there is absolutely no further charging of any description. The opposite of lead acid.
If you do need a battery to run an alarm, ventilation fan or whatever while in storage. Use a lead acid battery & charge accordingly, it is just a lot easier... & less chance of an expensive stuff-up.
This is a very long article, but be the time you finish reading it, you will be able to explain to others.
https://thegreynomads.activeboard.com/t67732755/lithium-batteries-charging-discharging-balancing/
I enjoy and read all the theories that abound on forums. Googxx links can be found to support all of them if you search enough. Believing is another story.
We have a 300Ah Sinolpoly 4 cell LiFePO4 battery that has now survived more than 8 years of full-time travelling abuse and at our last November annual c10 capacity test it can still deliver in excess of 4000Wh (c300Ah). Capacity is down less than 5% since new.
Our hands on daily use:
My aim is to keep the battery full but it has also spent 8 years higher than that often mentioned plucked from the air 50% SOC without significant capacity degradation. It should be dead by now. Lowest ever from memory = 54%. Capacity at dawn is typically 75-80% SOC.
Even worse apart from a few experiments with an H02 active balancer years ago the cells have never been balanced since the original careful top balance nor has it ever proved necessary.
Much, much worse according to another group of "experts" the cells should have self destructed long ago lying mounted on their sides for 8 years.
We must be lucky or perhaps the battery will only last 14 years and 10 months instead of its potential 15 years. At least I will never know.
All charging sources set to a 14.2V maximum. 75-80A alternator bulk forever once full while driving, up to 50A solar and the rare 30A mains charging. No absorption required. The battery is always 100% SOC at 14.2V regardless of charging current.
Then maintain 13.3V (float in lead acid talk) that equates to around 98% SOC for our battery.
Repeat next day.
Victron BatteryProtect low voltage cut off is set at 12.1V. Never triggered.
The battery also starts our 3.9l turbo diesel engine often multiple times a day.
These batteries are apparently far more forgiving than many would have us believe.
-- Edited by Scubadoo on Thursday 27th of October 2022 08:15:05 PM
-- Edited by Scubadoo on Thursday 27th of October 2022 08:26:25 PM
Welcome MHJM,
As you can see by what Scubadoo has posted there is all sorts of conflicting theories in regards to LiFeOP4 and I have got to agree with him.
The idea of keeping the batteries at 50% when in storage is based upon maximising the cycles and life of the battery. Interestingly though you can read about compression of the cells to also maximise the life of the battery but in all the battery tear down videos that I have watched I have never once seen any compression applied.
So in answer to your question of whether you need to float or trickle charge your batteries the answer is no, but you may have to take a check on them periodically, and a bit more often than 12 months. The reason being is that some BMSs draw a parasitic current and I found this out after not being able to access my caravan for 4 months. When I eventually got access to my van both batteries had gone from being fully charged to just under 10.5v. Everything, else had been switched off but I had not disconnected the BMSs.
I have decided that Im not going to worry whether I get 3,000 or 4,000 cycles from them and whilst in storage I have mine fully charged but with my inverter left on and drawing 0.9A at 12v. This is easily replaced on most days by my solar panels.
If you drain your batteries down a bit and then monitor the voltage for a while you will get an idea of the rate of self discharge. You are not going to harm them but just be aware that LiFePO4 has a very flat discharge profile and that the voltage drops sharply at the end.
Good luck.
-- Edited by TimTim on Friday 28th of October 2022 12:17:56 AM
I am not a techi, but I think a lot of confusion, comes from different manufactures of lithium battery/bms
I have lithium batteries from a mob called EVpower, which has the cell balancers on the battery, but a separate BMS (Battery Management System)
I am usually parked up for months at a time, and isolate the batteries at the BMS, and also isolate the solar panels from the DC/DC lithium profile charger
What I lose from the batteries, (if anything), is nothing to write home about
But, when I just isolated the solar panels, and 12 volt to the motorhome, I got parasitic current going to the BMS and DC/DC charger
This parasitic current ran down my batteries, in about 4/5 months
As already been said, I have not come across a manufacturer, who recommends to keep a lithium battery on a trickle charge
I have an Isolator Switch for the positive (+) to and from batteries.
When van resting at home, before next adventure, batteries get a rest, also.
They are isolated at full charge (13.5V), and after several months there is no noticeable storage loss.
However, if batteries are feeding any appliance(s) during storage then have charger connected. The BMS will disconnect/connect input charge so the batteries will still cycle.
LiFePO4 batteries are easy to manage as the BMS(s) does most of the charging/storage management.
Are you sure it's the BMS? Under zero load conditions I would expect the BMS to go into sleep mode where its current draw should be in the micro or even nano amp region.
Thank you so much for your comments and advice. It is certainly very helpful.
This is a great forum to draw on the knowledge and experience of the community.
A newbie who appreciates the feedback!! Regards MHJM
-- Edited by MHJM on Friday 28th of October 2022 01:59:08 PM
Surely the BMS would not be drawing any current, at rest or at any other time, but, the inverter drawing nearly 1.0A would draw down the battery(s) over time.
This parasitic current is too small for my el-cheapo clamp meter to measure
Even if this parasitic current is only 0.05 of an amp (50 milliamps), it would be 1.2 amps per day, or 8.4 amps each week, or around 33 amps each month
I do know that after somewhere between 4 to 5 months, when I went to check the batteries, the BMS had isolated itself from the battery at 10.5 volts
This meant that no more parasitic current went to the DC/DC charger and Bluetooth
From that time on, I have always isolated the batteries by switching the BMS off, and to the best of my knowledge, it completely stops any parasitic current
50mA (0.05A) is a huge amount of standby current for a battery system (in most cases). A few years past I was involved in the design of the Holden Commodore VE instrument cluster and we had a standby current specification of 16uA or about 1/3000 of 50mA.
These days I would expect most electronic systems in sleep mode to use close to zero current although, depending on the system, they may need to wake up perhaps once a second to check for external events but, in most case that will add very little to energy consumption.
Hi Mike,
I disconnected everything except the BMS on both batteries so did not expect any current draw. When I finally got back to my van the batteries were at different voltages and one was below the low voltage disconnect. It surprised me as my thoughts were similar to yours but then read on another forum where this has happened to a number of people. When i have some time I need to replicate and monitor what happens. I also need to test the high voltage and low voltage disconnects.
I took the batteries apart, did a top balance on the cells, and since then they been working flawlessly.
TimTim:
I can't recall what size batteries you own but, as an example, let's say 100Ah.
In 120 days they went from full charged to fully discharged say 90Ah.
90/120 = 750mA per day which is a considerable energy use for a battery system. Either the BMS is very poorly designed or something is wrong it seems to me.
A little Googling suggest a self-discharge rate of up to 5%/month for lithiums but there was one formal document (mainly behind a pay wall) which asserted that lithiums have a "memory" of being subject to excess temperature and will self discharge more in such a case. Dunno, but I am very surprised by your numbers... how do batteries waiting for sale in storage cope?
Interesting.
Hi Mike
I am not a techi, but there does appear to be some confusion, around parasitic current, with lithium batteries
I will try to explain in layman speak, why I think my parasitic current numbers was correct for my situation
Looking at the sketch below
When I isolate the incoming and the outgoing circuit breakers, I still have batteries feeding the BMS/DC-DC charger/Bluetooth as their lights are on
Specs of the DC/DC charger are
Snip below
But when I just push the isolation button on the BMS then nothing goes to or from the battery, as no lights are showing
And as far as I can tell, I lose nothing that I can measure from the battery
Hope that I have explained correctly
Hi Tony
It's hard to work out what is happening without more info. but it may be that some BMSs keep the Bluetooth, and other, systems active in order that consumers may check their battery's status. Consumers will like this but it will consume a fair bit of energy.
However I would expect that after a day or so when the BMS recognises the battery is in storage it would go into full sleep mode and minimise power consumption but perhaps it doesn't? This is really a design issue for individual BMSs.
Dunno :)
Would like to know the answer even though it does not affect my Lithium system, but still good to know.
My batteries (3) have integrated BMS to balance and manage charging levels. No external BMS.
I don't have Bluetooth integrated with Charger or BMS.
I don't have a DC to DC charger (not required).
If you isolate batteries(s) input/output positives, and batteries deplete to 10.5V over a period of time, then I would think there is a major failure somewhere.
Also, the later (3 way) fridges with AES need to be connected to 12V or won't operate.
As do, some, brake-aways that trickle charge a utility backup battery.
Hi Richard
If you are talking about my setup I think the reason for depleting batteries over a period of time, is probable different manufacturer of battery/bms/DC-DC chargers etc setups
When I mentioned that I isolated the incoming power, I only isolated the incoming solar cells/alternator power to the DC/DC charger
When I mentioned that I isolated the outgoing power, I only isolated the outgoing power from the external BMS to the house circuit
I still had the batteries sending power to the external BMS, which in turn sent power to the DC/DC charger, which in turn sent power to the bluetooth adaptor, as each of them had lights showing
My system works slightly different than your, and I shall try and explain
EVPower batteries of four prismatic cells, have a cell balancer on each cell, with an external BMS capable of controlling all the cell balancers
The idea of the cell balancer, as far as I am aware, is to balance the cells within a certain voltage, on both the charge and discharge cycle
If/when any one cell is over or under by, I think it is half a volt, the BMS will close down to protect the battery
If/when the incoming voltage is over 15 volt, or the battery is depleted to 10.5 volt, the BMS will close down to protect the battery
When I use the isolation button on the BMS to close the batteries down, then like your system, I have no power leaving the batteries or going to, the batteries
My DC/DC charger has both a alternator, and solar incoming connections, like your system I now only use the solar side of the DC/DC charger
Much like a normal solar charger
I find that 500 watt of roof solar, is more than adequate for my 12 volt requirements
I hope that I have explained it correctly
If not I will show you, if we meet up at Greens Lake (hopefully around January 2023)
Thanks for the clarification, Tony.
Would be great to catchup with you guys.
Yes Neolpolar, that is how EVPower suggested I wire mine up, as I only have 2 batteries, and up to date I do not require any more battery power. So the third connection was available
I did ask the question why, as the fourth connection clearly says charger/load or something similar
It appears that the method behind the madness, is as you have already pointed out, with the external BMS isolated, either automatically or manually
Nothing can go to or from the BMS, which means that nothing can go to or from the battery
Below is a pic with the protection cover, (which holds the manual isolation button), and buss bar of the external BMS removed, so others may understand a bit clearly
In storage always best to keep at 50% as a rule of thumb, once you go over 70% you will see the degradation long term. The whole point is to minimize side reactions which contribute to the build up of the oxide layers, this has been known for decades, anyone claiming otherwise doesn't have a clue.
I store mine at 35-40% to minimize any degradation, my bms has a noticable parasitic draw and so every 4 to 6months I need to top it back up to near 40%, technically 20% and stored in near fridge temps is best, this is true for most conventional li-ion cells, but LiFePo4 is a more robust, but for every guy who says "my cells are 9 years and doing great" there is another guy who complains his cells are just 7 years old and lost alot of capacity. Ultimately there are so many variables. I've seen cylindricals last 4 years until EOL 80%, yet others well north of 10. Some li-ion by themselves self discharge quite slow, some very slow. Again many factors like quality, luck, heat, SoC etc.
The reason dropins don't use compression is simple, cost, space and the fact it needs to be constantly baby sitted.
Our now more than 8 years old Sinopoly 4 cell 300Ah battery has dropped in capacity in Ah from the original 315 to a mere 301 at our last annual November annual C/10 capacity test earlier this month.
The battery has never been "stored". It is used daily and has spent perhaps 95% of its near nine year life at >70% SOC. 100% each day end and c70% each daybreak.
As mentioned in an earlier post if the battery life in fact been shortened I will never know or really care.
Now if a scientist with actual practical experience, not doomsday theorist, proved otherwise ...
We are not too concerned. We have had our money's worth already.
Im with you Scubadoo. I keep my batteries fully charged and although I started out compressing the cells I decided to take it off and just bind them together with Gorilla tape. Whether I get 3000 instead of 4000 cycles I couldnt really care.