Oldtrack 123 said

Hi J [!} The one metre run from the dc charger to the batteries will give0,078V drop at 40A with 5B&S[16.77mm2] 6B&S [13.3mm2 =0.099 Vdrop ,Which i would consider quite adequate 7B&S[10.55mm2] gives 0.124V drop [2]I would certainly use the B&S 0 [53.49mm2] for the battery parallelling jumpers [3] for the solar I would consider 6 B&S [13.3mm2]quite adequate with a0.099 VD [4 ] similar for the Mains charger would be ok for a charger up to 40A PeterQ

Surely you jest???? 

All of the suggested sizes above are pure overkill.

I rarely specified links as large as 50mm²  even for multi thousand Ah banks that we built.

50mm² has a carrying capacity of around 250 amps, and in a parallel connection the links are carrying only their relative proportion of the load, not sure that the OP will be dragging 500 amps from his 2 battery bank.

As a battery interconnection link, 8 AWG has a capacity of about 75 amps, so that would allow a draw of 150 amps with a voltage drop of less than 0.1v for the lengths specified, which is well within his likely loads.

Remember also that for most of the cables being considered here, the voltage drops are not cumulative.

brian wrote:

Surely you jest???? 

All of the suggested sizes above are pure overkill.

I rarely specified links as large as 50mm²  even for multi thousand Ah banks that we [1]built.

50mm² has a carrying capacity of around 250 amps, and in a parallel connection the links are carrying only their relative proportion of the load, not sure that the OP will be dragging 500 amps from his 2 battery bank.

[2]As a battery interconnection link, 8 AWG has a capacity of about 75 amps, so that would allow a draw of 150 amps with a voltage drop of less than 0.1v for the lengths specified, which is well within his likely loads.

Remember also that for most of the cables being considered here, the voltage drops are not cumulative.

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Hi Brian

Yes the battery jumpers are on the large size  but welding cable in that size is readily available

& possible connection losses also ned to be considered

& who know what size INVERTER J may finally decide on

I know different tables give different values based on a number of conditions

But a common table shows the continious rating of of 8AWG as 62A

 Based on J's 100A [surge current?] the voltage drop under that condition would be 0.16V

At 150A,  VD would be 0.247V!  

But just one other point ,you say NONE of the VDs are additive, perhaps you shoul look at the circuit & reconsider THAT statement!

I have just checked my figures for the solar& Mains charger & correct them.

At 40A the vd  to the  battery terminial would be 0.1036V  THEN there is the Jumper VD 0.03

total 0.1336V

Since the MAX recommended voltage drop with most solar regs being 0.2 V   between reg a battery it is on the safe side allowing allowing for any connection losses   

I think you would agree ,0.2V represents a significant difference in SOC of a battery

And the same should apply to the mains & DC to DC charger

Finaly what would be the COST difference for the small amount of cable involved ??  

AND for Bob,the weight difference??

PeterQ                                                            

-- Edited by oldtrack123 on Monday 2nd of December 2013 02:21:35 PM

-- Edited by oldtrack123 on Monday 2nd of December 2013 02:24:13 PM

oldtrack123 wrote:

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oldbobsbus wrote:

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..LOL... Brian,


Between the 2 of them by the time Peter finishes up loading up the bus with wire and SnowT loads it up with everything he wants in it he will need a HR license to drive it it will be that heavy...lol

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HI

Another very useful post??????

 

PeterQ

 

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 Ditto 

Juergen, the time is right to seriously consider LiFePo4 technology.

The weight saving is considerable for the same Ah, but you don't need as much Ah with them, and the total cost won't be that much different.

You can get away with roughly 2/3 of the capacity, again for the same usable Ah, they don't suffer voltage depression anywhere near as greatly, often holding over 12.5v even under sustained heavy loading, and because they charge so much more rapidly you can provide less solar capacity as well. 

There are numerous knowledgeable folk on the forums who know the ins and out of these batteries, and who are quite willing to assist you along the way.

brian wrote:

 

 

You don't need to be embarrassed to ask the question - if that's why you included this  symbol.

[1]As you should be aware, a lead acid battery is a very slow creature to charge due firstly to it's initial high internal resistance when in a low Soc, and secondly to the requirement for the charger to ramp down its charge rate to limit gassing once the battery reaches around 80% Soc.

[2]It accepts a reasonable charge early on in the process but then slows to a trickle long before the battery reaches full charge. This trickle can last many hours before the battery is truly fully charged.

[3]Often, even in the boost part of the charge cycle, and with high insolation, a lead acid battery is not accepting all of the available Pv capacity.

[4]There are just not enough peak sun hours in one day to enable a low Soc LA battery to be fully charged by a Pv array that is sized (battery to Pv capacity) to just utilise those peak sun hours. 

[5]Because of the internal resistance of the LA battery, even in the early charge stages a solar panel is often putting out only a fraction of what it could be doing if the battery could only accept it.

[6]To compensate for this, we then install more solar to take advantage of the lower insolation afternoon and next morning periods when the batteries could be accepting more than what the smaller solar could deliver. We then have larger capacity than the battery can accept at peak times, this is wasted.

[7]It is a simple conclusion that utilising a battery technology that does not have this limiting factor enables the Pv collector to be smaller.

[8]LFP technology fits this requirement, it can take all of the output that the panel can produce right up until almost full charge, and so therefore we don't need to add extra Pv capacity to compensate.

[9]For comparative amp hours used, the Lithium technology makes better use of Pv capacity than the lead acid by a good margin. This logically leads to the need for less Pv capacity for the same Ah usage patterns.  

[1o]Considering that LFP batteries have a longer deep cycle lifespan than LA types, can deliver larger discharge currents for longer with very little voltage depression, weigh considerably less and occupy a smaller footprint for the same usable capacity, charge faster, etc. etc. there is no doubt which is the better choice, and prices are getting down there as well. 

 

 

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Hi Brian

Let me start  by saying those words I questioned would lead e some to believe that one could get more Amphrs out of lipfepo4s than they have put in

This has been a common problem since this type of battery started to mentioned on fora 

Some of the apparent claims were absolutley ridiculous,even beyond perpetual energy

Claims have even been made they are 100% efficient in both charge & discharge cycles 

Now

[1]Yes ,agree advantage 1 is they can accept a higher charge rate right through the charge cycle  IF the solar capacity is there

[2]Yes, more so if only a PWM reg is used 

[3]Yes,, more so if only a PWM reg is used

[4]yes, if the panel system is undersized &  more so if a PWM reg is being used

[5]YES ,more so if a PWM reg is being used,

[6]I would expect that extra capacity to being suppling loads other than the batterries

[ 7] yes, I have no disagreement with that  in itself

[8]Yes ,the technolgy does that, but usually during the day, you should have excess capacity so other loads can be run  leaving the batterries for after hrs use

[9] by about 10to 15% I believe

[10]Yes, totally agree
IF I was starting from scratch,&intending to keep the unit for many many years,I would be seriously looking at LiPoFe 04 batteries

I do nothave a problem with the batterries or the technolgy

I do have a problem which seems to pervade the subject of these batterries performing miricles

Many users make massively impressive claims, like i can run EVERY thing all day  ,then give a list,yer when questioned on solar capacity to meet those claims go very quite!!

The part of your post I questioned could give that impression, IMHO.

One point that does not seem to be made is the care /control needed to ensure they are not OVERDISCHARGED or severely OVER CHARGED,that includes every single CELL in the bank

Over disharging a LA battery will shorten it's life, but will not kill it stone dead as can happen with LipoFe  cells.

Over charging a LA battery can also shorten it,s live but nowhere near the effect over charging can have on Lipofe CELLS

The relatively flat output voltage curve of LiFePos means one has to work between narrow limits of SOC, or have accurate cell monitoring, alarms , or cell equalising methods

But I know you are aware of that, it is just for other's info

PeterQ

Plendo wrote:

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Hi Brian and Peter,

I have just read your summary, and it is good to see agreement about the benefits of LifePo4, just one little clarification, Peter you stated:

"The relatively flat output voltage curve of LiFePos means one has to work between narrow limits of SOC, or have accurate cell monitoring, alarms , or cell equalising methods"

While I understand what you mean it is a bit back to front. 

The voltage of the LifePo4 cell stays relatively flat from 3.45V (95+% charged) down to about 3.18V (20%), multiply this by 4 for a 12v system, or 8 for a 24V system.

Add in voltage sag under load (small but still present), and voltage boost (depends on your charger) under charge and it does indeed become difficult to understand the SOC of a LifePo4 battery. By comparison you have to keep an LA battery in a narrower range of SOC to avoid reducing the life of the battery (which is already about 10% of LifePo4) but it is easy to tell where you are because the voltage drops through a much larger range. 

 

The range of State Of Charge (SOC) you can use with a LifePo4 is typically between 95% and 20 to 30% which is very broad when compared with other common battery technologies. 

 

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HI Plendo

I believe we are saying the same thing regarding monitoring SOC of LiFePos

Yes,  the depth of discharge that the LiPoFesCELLS can be taken down to to is quite low compared to any LA batterry BUT  the very nature of the voltage curve[safe range of 0.27V] means it is relatively flat. until the cells are very close to being either fully discharged or fully charged

Remember it is the individual CELLS we need to be concerned about .,not the ovevall bank voltage

Working close to those limits allows litle range for errors.

At this stage the need for cell balancing is a bit of an unknown, IMHO, as few such batterries have had anywhere near the claimed live cycles in actual everyday use

Despite what some may say, CELL  monitoring to limit the possiblty of over discharge & that resulting in reverse charging of an indivual cells is essential.

One cell in a bank goes too low it, starts to reverse charge virtually Stuffed , but when recharging  others in the string will overcharge while trying to bring the string up to voltage !All stuffed  very quickly

The situation is even more critical with  series parallel set ups ,even a slightly minor  variation resistance in the connection can be significant

Some users seem to be getting a liitle compla,cent because the cells have not drifted much out of balance so far , but most of those have only be in use a short time

It will be interesting to see how well they stay in balance as they age

But As I said IF I was starting over again, I would certainly be looking to use them!!

Sadly ,due to health problems THOSE days are over ,. just sold the motor home.

PeterQ

Hi Plendo

Good to see you did not just jump in

Yes, you are on the right track , those sudden changes at each end of the charge/ discharge curve need to be kept well clear of

It seems YOU understand my post. 

Also be aware that even a slightly dirty/ poor connection can upset the all apple cart If those low & high point monitoing points include those poor connections[false voltage readings]especially if taken when batterries  have a load, or are charging.

To minimize the error, try to get the various senser leads DIRECTLY ONTO THE CELL TERMINALS

PeterQ 

-- Edited by oldtrack123 on Friday 6th of December 2013 11:55:21 PM

Hi terry..

Yes I do understand the short fall's of AGM battery's..

Initially I was looking at 480Ah batteries because I'm aim to use a Max of 30% of the battery capacity to run what I need..
My think'n is that the less I drew down the Longer the battery will last, therefore the Longer the life cycle of the battery..

I'm have done a bit of research regarding the Depth of discharge to charge cycle life.. and my initial thought's is go as big as I can afford to save in the long run..

I have just found the Winston batteries, but the question's are, I don't know enough to be able to full use the batteries to their full capacity and there is an extreme lack of information around..
The fact that the LeFePo4's have replace the first generation of Li Batteries is the biggest step..

I did do some rough pricing and I can get a 300Ah LFP for a reasonable Price But I'm not sure about the rest of the gear to be able to use them safely..

I'm still looking so I understand the full ramification's of Li batteries..
I DO NOT want to screw up..


Juergen

Good morning how was the happy hour we had ours at anyson res last night ok