Lithium battery re start

Pradokakadudavid · Senior Member

Lithium battery re start

Corndoggy · Senior Member

A usual way to do this is connect another power supply to your dead batteries. This could be a charged up battery or a charger in power supply mode. If your victron solar controller can be set into that mode you could use that. The theory behind this is to get some charge into the battery before you try charging from a charger. I just did a run through this over the weekend. My battery wouldn't charged straight from shut-down without giving it a kick-start. I could do it with my 240v charger in power supply mode, my 240v charger in power supply mode running the input of my dc-dc charger in power supply mode, but couldn't check the solar controller as my charger couldn't be set high enough to start the controller.
Though I have seen it stated by a brand that you need their power supply to restart their batteries. Could be a sales pitch though.

TimTim · Guru

What brand of batteries do you have as some actually have a restart button to activate the BMS in the battery. 20% is a high threshold for the BMS to turn off although there one brand of battery that will only discharge down to 20%.

The battery voltage will be too low for many solar controllers to kickstart and i cant recall if my Victrons will or whether my Victron 240v charger can. I need to refresh my memory. Im sure the voltage would be too low for my Redarc also.

As Corndoggy said, probably the most simplest method is to hook up in parallel with another battery and connect a charger then simply disconnect the other battery.

Tim

Pradokakadudavid · Senior Member

Thanks guys excellent advice.

Not sure what brand of batteries I have as they came with the caravan when new.

It is pain in the arse to remove the seat covers to check the batteries but I guess this would be a good starting point.

I have one of those itech battery jump starter thingos so I will ask itech tomorrow if this is suitable as a lithium battery restarter.

I guess the best strategy is to not let your batteries get too low and I usually monitor this through my Redvision system.

It will never be a problem when the sun is shining as I have 1.2 kw on the roof (6 panels) but in cloudy conditions when off grid, this could be a problem.

Thanks for the advice.

Cheers.

David.

TimTim · Guru

Perhaps I should say I build my own batteries and have undertaken the kickstart I have described.

One thing that may not be well known is when the BMS goes into sleep mode, in some cases the battery voltage across the terminal will drop to around the 5.0V mark or not show a voltage at all. I know this has caused concern for people and they then think their battery has suffered irreversible damage. This is not the case as the battery will generally be at or around the BMS disconnect voltage which may be around 10.0V. It is just that the BMS shows a much lower voltage. A voltage check of the 4 individual cells confirms this but of course with sealed batteries you are unable to confirm this.

David, it would be good if you could get a link to the product your friend has.

Tim

Dick0 · Guru

Hi David,

This should help solve the dilemma.

Watch this video from beginning.

3 Ways To JUMP Start And WAKE A DEAD Lithium LiFePO4 Battery FAST! (youtube.com)

-- Edited by Dick0 on Monday 8th of April 2024 12:17:41 PM

Radar · Guru

Very interesting topic and hope we get a really good answer to a problem that could arise from running our Lithium Battery to low.

We rely on our battery for our LED lights and the occasional water pump use and recharge with solar.

Hope we get a good Layman's answer.

Pradokakadudavid · Senior Member

itech tell me that my itech jump starter, model number 2000A will work to restart my caravan lithium batteries. Currently $199 reduced from $350.

The product that my mate has is a Jaycar 12v 850A jump starter and powerbank currently priced at $289.00.

Cheers.

David

Dick0 · Guru

Pradokakadudavid wrote:
itech tell me that my itech jump starter, model number 2000A will work to restart my caravan lithium batteries. Currently $199 reduced from $350.
The product that my mate has is a Jaycar 12v 850A jump starter and powerbank currently priced at $289.00.
Cheers.
David

Not necessary to fork out that sort of coin for something so simple to solve.

A power bank starter, however, is handy to start the vehicle when vehicle battery is flat.

StormCamper · Member

Usually if the BMS senses a live voltage acros the batts terminals/bank terminals say from any source (charger, another battery) it will engage (turn back on). However many chargers won't output a live voltage unless they themselves can sense the batteries voltage. So this is were having a charger that allows to be used as a power supply mode (it actually has a constant live voltage all the time) is better than those pre canned profiles and smarts. My AC charger for example does just this, no nonsense nanny state smarts to slow me down in life.

20% is way too high for the bms to shut off, very wasteful. The bms should shut off at ~2-4% at worst. Some bms will turn back on as the cell voltage inevitable rebounds back over 3v/12v pack voltage. A good rule of thumb is cycle down to 90%, that 10% is your reserve tank. Of course, there are other valid approaches like 50%, 30% for different environments and needs.

TimTim · Guru

Unfortunately the make of battery that I stated that had a low voltage cut out at 20% was one of the more expensive brands. Charging was also stopped at 90% so in effect one could only use 70% of the stated capacity. I cant recall whether it had a Bluetooth BMS but in many cases even when they have Bluetooth incorporated the maximum and minimum voltages set in the BMS are not adjustable. Therefore in such cases it is important to note the high voltage and low voltage disconnect.

The main thing to remember is if your BMS does go into low voltage sleep mode, the battery has not died smile .

Pradokakadudavid · Senior Member

Thanks all.

My lithium battery shut off voltage (%) is whatever the caravan manufacturers set it to.

I thought it was 20% but perhaps I dreamed this somewhere!

Is there any way I can tell what the shut down voltage is apart from draining the batteries to see what the shut down point is???

Cheers.

David.

Corndoggy · Senior Member

Would think the low voltage setting in the battery would be set by the manufacturer of the battery, not the caravan manufacturer. Unless your bms has a function that allows you to see what's going on in the battery there is no way to tell what it is set to, never mine adjusting it. These batteries hold a constant voltage, to a degree, while discharging and get to a point that the voltage falls off steeply when discharged. The bms shuts down the battery to stop damage from to low a voltage. Think the easiest way is sit and watch your battery discharge when it gets to a point of shutdown. Does your van bms give you information on charge/discharge of the batteries?

TimTim · Guru

As Corndoggy stated the low voltage disconnect is based on the battery manufactures BMS settings unless you have an App and Bluetooth to view and edit the settings.

The specifications for make and model of battery may reveal a little more.

-- Edited by TimTim on Wednesday 10th of April 2024 06:32:31 PM

Corndoggy · Senior Member

Would also say a more important figure to look at is the charge/discharge AH of the battery. That should give a good indication how the batteries are going.

Radar · Guru

This is what our battery has displaying on the outside of the battery.

I do carry a very old set of jumper leads.

Just hope we do not allow the battery down to that point.

IMG_20240402_132558_022~2.jpg

Pradokakadudavid · Senior Member

Answers to some questions above:

The equipment that I have under the caravan seat is:

1. Redark 3000w inverter (I thought it was 4000w but obviously not!)

2. Victron MPPT 150 60 MC4 solar controller (what ever that means?)

3. Power lithium LFO 12.8V 135 A/H (three of these).

4. Red Vision display.

5. Redark BMS (big grey thingo!)

Interesting to get the facts from the source as I had other ideas about power outputs etc.

The red vision (not the redark BMS under the seat) display does indicate the percentage the battery is at and how much charge you have left until "flat" or maximum discharge level.

Hopefully you can tell by my naive, ignorance, that I have very little, if any, knowledge of how these electrical systems work!

I just turn things on and hope that it keeps working although I do keep a close eye on the revision monitor to see how much power I have left.

Cheers.

David

Dick0 · Guru

Pradokakadudavid wrote:
Answers to some questions above:
The equipment that I have under the caravan seat is:
1. Redark 3000w inverter (I thought it was 4000w but obviously not!)
2. Victron MPPT 150 60 MC4 solar controller (what ever that means?)
3. Power lithium LFO 12.8V 135 A/H (three of these).
4. Red Vision display.
5. Redark BMS (big grey thingo!)
Interesting to get the facts from the source as I had other ideas about power outputs etc.
The red vision (not the redark BMS under the seat) display does indicate the percentage the battery is at and how much charge you have left until "flat" or maximum discharge level.
Hopefully you can tell by my naive, ignorance, that I have very little, if any, knowledge of how these electrical systems work!
I just turn things on and hope that it keeps working although I do keep a close eye on the revision monitor to see how much power I have left.
Cheers.
David

Hi David,

You have 405AH of battery storage and over 1000W of solar. You don't need to be worried of not having full charge whether the sun is shining or not.

I assume the inverter is a 1500W/3000W or a 3000W/6000W capacity. You didn't specify. In any case, heaps of battery storage for 240V appliances unless you want to run the aircon for eight hours.

Keep just turning things on as required. Check the charge controller monitor before daylight in the morning to see the rested battery condition (SOC).

TimTim · Guru

Radar,

Great to see they have put the jumpstart instructions on your battery. The BMS cutout is at 9.2A which is probably way below what your 12V appliances will run at So you arent going to reach that level. Probably the only way you are going to reach such a low voltage is if you drew your batteries right down and then left them for a couple of months without recharging.

Free to Fly · Member

TimTim can you expand a bit on your comment that you build your own batteries please? Interested as I think many batteries are overpriced. Cheers Free to Fly

Scubadoo · Veteran Member

Just don't let them get below 20%.

Any decent BMS circuitry should isolate the internal cells well before they reach any critical discharge/voltage point. Automatic reconnection or not is an inbuilt BMS parameter.

Our 10 year old 300Ah LiFePO4 has no such BMS inbuilt to current limit battery output.
It has also started our 3.9l turbo diesel engine for those 10 years of fulltime travel often multiple times a day.

20%? Our battery has never been below c34% SOC in normal use. Hopefully an alarm will scream at 20% and cut off will occur at 10%. Still enough to start the truck engine with ease. Tested on day one of installation.

TimTim · Guru

Free to Fly wrote:
TimTim can you expand a bit on your comment that you build your own batteries please? Interested as I think many batteries are overpriced. Cheers Free to Fly

Many of us buy nominal 3.2V prismatic cells and a BMS from China we then assemble them into a battery. Obviously if you already have a few electrical tools then the cost is cheaper but if you have buy things like a power supply, crimpers then the cost does not work out cheaper but you get a quality batter plus tools.

You can buy a reasonable quality battery from say Aussie Batteries or you can also pat 3 to 4 times the price for a battery with the same quality cells inside.

We all chat about small systems consisting of maybe 1 to 4 batteries whereas as in Canada and the US people are using much larger banks of batteries and cells and these are the only means of power that they have except for a back up generator.

Some good links are,

https://diysolarforum.com/

Plus we cant forget about Andy

https://diysolarforum.com/

Message me if you want any further information so as we are not clogging the thread.

TimTim · Guru

Pradokakadudavid wrote:
Answers to some questions above:
The equipment that I have under the caravan seat is:
1. Redark 3000w inverter (I thought it was 4000w but obviously not!)
2. Victron MPPT 150 60 MC4 solar controller (what ever that means?)
3. Power lithium LFO 12.8V 135 A/H (three of these).
4. Red Vision display.
5. Redark BMS (big grey thingo!)
Interesting to get the facts from the source as I had other ideas about power outputs etc.
The red vision (not the redark BMS under the seat) display does indicate the percentage the battery is at and how much charge you have left until "flat" or maximum discharge level.
Hopefully you can tell by my naive, ignorance, that I have very little, if any, knowledge of how these electrical systems work!
I just turn things on and hope that it keeps working although I do keep a close eye on the revision monitor to see how much power I have left.
Cheers.
David

Hi David,

1. Looks like you have a straight 3000W inverter but this will run all your 240V appliances and even your AC and more so if it has a soft start.

2. The 150 is 150V the maximum voltage it can accept and the 60 is 60A the maximum current it can produce. Your system will have been built taking these parameters into consideration so you do not need to worry about them.

3. It would appear that your Power Lithium batteries have a cut off of 8.0V judging by the specifications of that brand. Although it is recommended that the cells not be taken below 10.0V the drip down to 8.0V would happen very quickly. As i have already posted your 12V appliances will have cut out before then. Furthermore your Redarc system will have a low voltage cut out which you can set manually.

i dont think you need to worry about your batteries going into sleep mode judging by the quality of the system you have.

Tim

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