Max charge for LFP

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SteveK

SteveK

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Joined
Jul 5, 2019
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Location
Gulf Islands, BC Canada
Vessel Name
Sea Sanctuary
Vessel Make
Bayliner 4588
Depends on the brand. What I am finding is that the max charge is not freely given for a bank of batteries but rather one of the batteries in the bank. For instance a 100 Ah battery I looked at said max charge 50 amp, that is 50% right. So if I install 8 of these for 800 Ah can I conclude a max charge of 400A?

Depends on the brand. It can be anything from 20-50% max charge. Some even say in an emergency 100%.
Is there any solid info available for a multi bank LFP.
BTW, I am less concerned about long life and more concerned about fast re-charge.
 
SteveK said:
Depends on the brand. What I am finding is that the max charge is not freely given for a bank of batteries but rather one of the batteries in the bank. For instance a 100 Ah battery I looked at said max charge 50 amp, that is 50% right. So if I install 8 of these for 800 Ah can I conclude a max charge of 400A?

Depends on the brand. It can be anything from 20-50% max charge. Some even say in an emergency 100%.
Is there any solid info available for a multi bank LFP.
BTW, I am less concerned about long life and more concerned about fast re-charge.
Click to expand...

I dont really like the way many brands show the ratings of charge and discharge. I would like a more standardized method.

But in general yes you can add the rated amps from a single battery and extrapolate to multiple.

If you are looking into purchasing and you are looking at some 100ah batteries please be aware most batteries are limited to 4S4P. Meaning you would only be able to go with 4 of the 100ah batteries in parallel for 400ah. You could then go another 4 in series for a 48 volt 400ah battery. But that does little good if you are a 12 volt system. So then you need to look into 200ah units that can be assembled into 4s for 800ah.

If you are looking for quality batteries I have been a fan of Kilovault and Epoch. Unfortunately Epoch hasnt had a large battery...until now.

300AH battery
300amp continuous discharge
900amp peak for 3 seconds
300 amp continuous charge
Capable of 4 in series and 4 in parallel
internally heated
Bluetooh
direct Victron Comm capable
UL1973, UL1642, IEC 62133, UN38.3

All that for $1199 and easy to find 10% off coupons

I just ordered a pair. Expected ship date is Aug 17.
 
But in general yes you can add the rated amps from a single battery and extrapolate to multiple.
Click to expand...
This is what I wanted to hear, though charging at 400A will be another test of patience to find.
 
Barking Sands said:
Yes, but Be sure the battery you choose allows for more than 4 batteries in parallel. I havent seen any.
Click to expand...

This is another one of those maybe things. What I read, the 4 battery parrallel is to allow BMS to self balance, more than 4 and maybe not. But nothing read to say dont do more than four otherwise. So maybe I will do two banks of 4, charge each separate, then combine for use.

BTW, some batteries recommend just 2 parrallel. Depends on the brand, they are not created equal
 
No..definately not. Some are not great at all.
Victron claims 5. I was going to try 6 but ultimately decided against it.
Another way was to use some number of batteries dedicated to an inverter and the rest for dc only.
Like 400 ah for inverter and 200 ah for dc systems only.

But ultimately I just decided on larger ah batteries. Much less connections, much less wiring and wiring runs etc.

But I alsi wanted more than 1 single batt for redundsncy.
 
A bit surprised with all the threads and people with LFP that we are not getting this is what I do.

I have 840Ah fla so can use 1/2 or less frugally. Want double usable Ah to 800Ah approx. But the issue is how to charge them without running the GEN for 6-8 hours, that seems wrong.
I have calculated an average want for 25-30A hourly which would require recharge every day.

Anyone with what works for you, your average load, bank size, charger(s)
 
Changing from acid to lfp doesn't change any of your current charging except for faster charging the last 15%, if you don't want to have to run generator every day you need passive charging, solar.

Besides the usable capacity the big plus of lfp is they don't care if you "only" recharge to 85-90%, but acid really does care,
 
SteveK said:
A bit surprised with all the threads and people with LFP that we are not getting this is what I do.

I have 840Ah fla so can use 1/2 or less frugally. Want double usable Ah to 800Ah approx. But the issue is how to charge them without running the GEN for 6-8 hours, that seems wrong.
I have calculated an average want for 25-30A hourly which would require recharge every day.

Anyone with what works for you, your average load, bank size, charger(s)
Click to expand...


I'm not really understanding the question(s).


If you want a bank that is 800Ah, then recharge will be the charge current * hours to produce 800Ah. So 200A would recharge in 4 hrs, aka a .25C charge rate. Or if you want to recharge in 2 hrs you need 400A of charge current, aka a .5C charge rate. Most manufacturers want regular charge rates to be in that range. Max charge current will also be limited by your shore power and/or generator capacity.
 
TT, the max charge question was answered that if one of eight can be charged at 50% then all 8 can be for a total of 400A max.

OK let me ask a different way. Say in 24 hours I use 600 amps.
I have a 8KW generator to power chargers. Currently the Magnasine is rated for 120A but the most I have seen is 115A and then it tapers off to keep from overheating, was seen at 85A. I have a 4 bank 60A charger which has not shown 60A continuous charge, maybe it is 15 per each line. Say I can continuously charge 100A, it would take 6 hours. Do not have solar installed, but the basic kit I bought for the other boat puts out about 20A. Off the engine I will have 100A DC2DC, still 6 hours engine hours.

What chargers do you recommend to say charge 200A.
 
SteveK said:
A bit surprised with all the threads and people with LFP that we are not getting this is what I do.

I have 840Ah fla so can use 1/2 or less frugally. Want double usable Ah to 800Ah approx. But the issue is how to charge them without running the GEN for 6-8 hours, that seems wrong.
I have calculated an average want for 25-30A hourly which would require recharge every day.

Anyone with what works for you, your average load, bank size, charger(s)
Click to expand...
We use around 300 Ah @ 24 vdc daily. I replaced 1280 Ah of LA with 600 Ah LFP. I recharge daily using 90 A from the Inverter/Charger, plus three 30 A Sterling chargers in parallel, so re-charge takes a bit less than 2 hours daily. In a pinch, I can add another 90 A from the alternator if I'm running the main. When charging, my Lithionics LFP accept 99% of charge current up until about the last 5 minutes of the charge cycle. Lithionics balances cells at 14.6/29.2 vdc, so that's the peak voltage they recommend with minimal absorption and no float stages.



There is no point, IMO, installing more LFP capacity than double daily usage. If you install 4 x daily, you'll be running the genset every other day, but for twice as long when you do, so total run time is unchanged regardless of the size of the bank.


How many batteries you can string together is, I believe, largely a function of the quality of the BMS. If its internal wiring or the internal wiring between individual cells is less robust, that puts a limit on charge/discharge current. Rod Collins covers this topic well here:


https://marinehowto.com/drop-in-lifepo4-be-an-educated-consumer/
 
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SteveK said:
TT, the max charge question was answered that if one of eight can be charged at 50% then all 8 can be for a total of 400A max.

OK let me ask a different way. Say in 24 hours I use 600 amps.
I have a 8KW generator to power chargers. Currently the Magnasine is rated for 120A but the most I have seen is 115A and then it tapers off to keep from overheating, was seen at 85A. I have a 4 bank 60A charger which has not shown 60A continuous charge, maybe it is 15 per each line. Say I can continuously charge 100A, it would take 6 hours. Do not have solar installed, but the basic kit I bought for the other boat puts out about 20A. Off the engine I will have 100A DC2DC, still 6 hours engine hours.

What chargers do you recommend to say charge 200A.
Click to expand...


https://www.amazon.com/Sterling-BB1...ocphy=1013962&hvtargid=pla-570558652535&psc=1
 
Delfin said:
How many batteries you can string together is, I believe, largely a function of the quality of the BMS. If its internal wiring or the internal wiring between individual cells is less robust, that puts a limit on charge/discharge current. Rod Collins covers this topic well here:


https://marinehowto.com/drop-in-lifepo4-be-an-educated-consumer/
Click to expand...

Was there another section refering to this. The only part I have seen in that article was the following:

Maximum Parallel Configuration : (Identical Model Batteries): Do not exceed this number!
Maximum Series Configuration:(Identical Model Batteries):Do not exceed this number!
Click to expand...



I figured if you had very high quality cells that are selected and batched with a tight variance, and that variance is maintained over thousands of batteries this would lower the likelihood of balance issues when grouping batteries together. At least for dumb, non-communicating batteries. But really hvent heard a great explanation for this restriction.


The batteries that have inter-battery communications in theory should be able to solve this.

I know Epoch has a 48 volt 30AH battery intended for golf carts which has inter-battery charge coms. For those you can stack up to 10 units in parallel.
And I have also seen external balancers for batteries in both series and/or parallel that are meant to solve that issue.

I know with my old dumb Dakota 12 volt 100AH units in series in my golf cart I had some balance issues that caused a shut down. Easy to bring back in balance but I was caught by surprise. Its the main reason I sought out a battery with bluetooth.
 
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OK, if you want to charge a 600Ah bank is 2hrs you need 300A. Or 200A to recharge in 3hrs. To me that's a reasonable range acceptable to most all battery vendors, and reasonable generator run duration.


If your Inverter/Charger can produce 100A if kept cool, then you need 100-200A more. Victron makes a Centaur charger that is 100A, so one or two of those would do the trick. If your 60A charger only produces 15A usable into a single bank, I would dump it.



Of course I'm assuming a 12V system. Note sure if that was ever stated or not.
 
Barking Sands said:
Was there another section refering to this. The only part I have seen in that article was the following:
Click to expand...
Quite a ways down, under "Important BMS considerations" and following he discusses the issue, noting the differences between good and not so good construction. I've looked at the Lithionics site, and I can't find any limitations on how many of their batteries can be paralleled. There may be one, but I can't find it.
 
Delfin said:
Quite a ways down, under "Important BMS considerations" and following he discusses the issue, noting the differences between good and not so good construction. I've looked at the Lithionics site, and I can't find any limitations on how many of their batteries can be paralleled. There may be one, but I can't find it.
Click to expand...



FYI, my MG batteries have no limit on paralleling either.
 
Increasing your alternator output capability can help the equation considerably, especially if you run the boat most days.

Our boat is pretty power hungry. Over time, we added solar, increased the gen charging capacity with additional chargers, and upgraded to a 2-alternator charging system for our house (LFP) bank. Now we mostly only run the gen when we need it for something else and, between the multiple charging sources, everything stays charged.

It is nice not having to nurse the AGMs through the taper and make sure they are regularly brought to 100%. We just pour amps into the LFPs when it makes sense with big AC chargers (Victron) but the alternators and solar really do most of the work over time.
 
guy with a boat said:
Increasing your alternator output capability can help the equation considerably, especially if you run the boat most days.

Our boat is pretty power hungry. Over time, we added solar, increased the gen charging capacity with additional chargers, and upgraded to a 2-alternator charging system for our house (LFP) bank. Now we mostly only run the gen when we need it for something else and, between the multiple charging sources, everything stays charged.

It is nice not having to nurse the AGMs through the taper and make sure they are regularly brought to 100%. We just pour amps into the LFPs when it makes sense with big AC chargers (Victron) but the alternators and solar really do most of the work over time.
Click to expand...


Pretty much the same for us.
 
With Victron you can parallel up to 6 multiplus inverter/chargers together to get a higher charge output.

I parallel two of them, and the setup is pretty easy.
 
ksanders said:
With Victron you can parallel up to 6 multiplus inverter/chargers together to get a higher charge output.

I parallel two of them, and the setup is pretty easy.
Click to expand...
Kevin, is the Multiples programmable with respect to bulk and absorption charge voltages? From the brochure it looks fixed.
 
ksanders said:
With Victron you can parallel up to 6 multiplus inverter/chargers together to get a higher charge output.

I parallel two of them, and the setup is pretty easy.
Click to expand...

Are you using 2 of them for more AC output or just for more charging?

I've got a single Multiplus which handles my AC needs. I do need more charge capability so am debating between a 2nd MP or a simple 100A charger.
 
Delfin said:
Kevin, is the Multiples programmable with respect to bulk and absorption charge voltages? From the brochure it looks fixed.
Click to expand...

Their data sheets don't make it at all clear but the voltages are fully programmable.
 
Delfin said:
Kevin, is the Multiples programmable with respect to bulk and absorption charge voltages? From the brochure it looks fixed.
Click to expand...

You can choose from several profiles, or make up your own.
 
danderer said:
Are you using 2 of them for more AC output or just for more charging?

I've got a single Multiplus which handles my AC needs. I do need more charge capability so am debating between a 2nd MP or a simple 100A charger.
Click to expand...

I use two of them to increase my max charge current.

I have 840 AH of FLA batteries that can accept 200A charge current. With only one multiplus and my boats normal loads I only get a bit less than 100A into the batteries.

With two I get the full 200 with my input AC current limit set at 35A for the two of them combined.

If i do not run anything else on the inverter this continues until the batteries reach 14.3 at which point the State of Charge is in the mid 80% range. Then the current starts to drop off as the chargers hold the 14.3 voltage.
 
danderer said:
Are you using 2 of them for more AC output or just for more charging?

I've got a single Multiplus which handles my AC needs. I do need more charge capability so am debating between a 2nd MP or a simple 100A charger.
Click to expand...

We have stacked Outback inverter/chargers and added 2 Victron Skylla 100a chargers. For us, that was the most cost-effective way to increase our charging capacity. This is for an LFP bank, so it will take a fast rate of charge. FWIW, we don't exceed .5C charging rate.
 
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