Ah series / parallel Need 38120 advice

[izifaddag]

This forum has a lot of members and I am banking on one of them being an electrical expert. 
I have spent most of my life involved in electronics but sometimes I get confused. I am fedup trying to think this particular problem through myself, so I am asking for help as I just can't seem to arrive at a suitable answer. Mobile living has caused me to rethink an entire area of electronics that I thought I had mastered. I was wrong. I haven't.
Here are the facts.
I am building my own battery bank and I have opted to use Headway 38120s. I bought 16 used ones at a cheap price in April. I finally got to the point I could wire them into my build and 2 died going down to 0.45v apiece. One puked. I threw them away.
The remaining 14 were fine. 
These are rated at 8ah apiece and will push 200 amps before destruction. They are powerful. 
I bought 2 more rated at 10ah to replace the trashed ones.
I then mounted them in a 4S config to give me 12.8 volts. So that is 4 blocks each in 4S where the idea is to parallel them to spread the current pull nicely. 
I have 4 small BMS boards. They came from eBay and can handle 100a each. I did it this way so that each and every battery will be monitored rather than a block being monitored. I know it is a bit excessive but I thought it would be a good idea with 38120s. If it was 18650 I probably wouldn't do that.
I have been told that my 4S config is only going to yield 8ah. I thought that 4S would give 4 times 8ah. So 32ah for each battery block. This has totally confused me.
It would mean that the whole battery is only going to yield 32ah. I find this very hard to believe but this is what I am being told by someone who is an expert. It doesn't make sense to me. I was thinking add up all the ah and that was the total for the battery so that would be 8ah x 14 =  112 then another 20ah for the 2 odd ones. A grand total of 132. I'm stumped.  
Can anybody out there give me some advice on this calculation or maybe a different config. Has anybody else used 38120s. 
I'll check back and see if anybody has any advice. Thanks in advance.

 

[izifaddag]

I am probably going to want to expand this battery bank once I add solar and find my feet a little. I am happy building batteries but I need to get to the bottom of this before I make a mistake.
I think I'll check YouTube again then come back here.

 

[abnorm]

The 4 in series yield 12+ volts at 8 AH......X 4 in parallel = 32 TOTAL AH at 12 volts...……………...they're TINY

 

[bass_sears]

Let's keep the math simple and go with your original plan, 16 8ah batteries.

Each battery is 3.2v (right?), so you'd have 25.6 watt hours (3.2*8) for each battery, 16 of them is 409.6 watt hours (16*25.6).

409.6 watt hours at 12.8v is 32ah, so your whole battery pack will put out 32ah at 12.8v.

Remember, anything in series doesn't increase your ah only your volts, so each "block" is 8ah at 12.8v (four 3.2v batts in series), wire those four "blocks" in parallel and you get 4x8ah @ 12.8v or 32ah @ 12.8v.

If you just take the ah and multiple by number of batteries (like you did in your last example) you're working like you're putting them all in parallel... with your 14 8ah and 2 10ah batteries you can get 132ah, but only at 3.2v.

-- Bass

 

[izifaddag]

The 4 in series yield 12+ volts at 8 AH......X 4 in parallel = 32 TOTAL AH at 12 volts...……………...they're TINY

Let's keep the math simple and go with your original plan, 16 8ah batteries.

Each battery is 3.2v (right?), so you'd have 25.6 watt hours (3.2*8) for each battery, 16 of them is 409.6 watt hours (16*25.6).

409.6 watt hours at 12.8v is 32ah, so your whole battery pack will put out 32ah at 12.8v.

Remember, anything in series doesn't increase your ah only your volts, so each "block" is 8ah at 12.8v (four 3.2v batts in series), wire those four "blocks" in parallel and you get 4x8ah @ 12.8v or 32ah @ 12.8v.

If you just take the ah and multiple by number of batteries (like you did in your last example) you're working like you're putting them all in parallel... with your 14 8ah and 2 10ah batteries you can get 132ah, but only at 3.2v.

-- Bass

Thanks to both of you. This has helped tremendously. This is the reassurance I needed. The new math I came up with is the correct one and the original one is bad.
I have a slightly greater than 32 amp hour battery - remember that I have 2 incorporated into one block at 10ah.
This is very disappointing. 
I will need to beef this up by a factor of 4 to do and good.  So far I have spent on a total of 18 batteries, holders, BMS boards, cabling, terminals. Now I am faced with increasing this with 3 more setups exactly the same. This is starting to get a lot more expensive and heavy. I need to think about this.

 

[izifaddag]

I just added this up and it is coming to about $270 plus. All for 32 amp hours.
It would be cheaper to buy the Mighty Max for $800 and have done with it. 100 ah all in one package with no fiddling around. BMS is onboard.

 

[DLTooley]

The lifepo4 market is evolving quickly and prices are dropping, but not so much on the retail end.

I’ve seen figures reported recently of $150-200 per kWh and a forecast of $100 in a couple years. That’s a huge margin over retail prices for 100ah/1200 wh products in the market.

I’ve been poking around alibaba and aliexpress a bit, but shipping and quality control are big issues. You can buy batteries without bms at a discount and a quality controller should substitute.

 

[jonyjoe303]

270 dollars for a 4s 32 ah is not bad for highend lifepo4 cells that you can jumpstart a car with. For comparasim a goal zero 400 lithium is in the 700 dollar range for 40 ah.

I build my own lifepo4 battery packs, I have a 4s 220ah (4x 55ah 4s10p in parallel) house battery. I prefer having full control, use whatever bms for my own needs. 

Even with powerful cells you don't need 4 x bms. I have a smaller 4s 30ah battery using 72x A123 lifepo4 cells. (70 amp continous discharge 120 peak) and I am only using one 30a bms. With 4x bms, if one block of batteries stop accepting charge the voltage of the pack will drop to 9.6 volts and trick the charger to push max amps into the pack, it might cause voltage surges.

In your battery just connect all 4 of them in parallel and then connect the balance connectors between each pack together also, just make sure they are all the same voltage when you connect together. Once connected together the pack will equalize and you will have one large 32 ah battery.

I had this lifepo4 battery for the past 2 years, in the picture it only shows two 55ah 4s packs, I have 4 of these connected together in parallel for a total 4s 220ah.
I only have one bms to manage everything.


2 packs are in a group 34 case

 

[brahmon]

lotta brain power in this forum. way over my head. lol

 

[izifaddag]

I investigated the Mighty Max option. It really is the best way to go. Unfortunately they have gone up $25 since I first looked at them. $675 each ouch!
I plan on buying 2 and 2 100 watt panels to start. My enclosed cargo trailer has a ton of space on the roof so I will expand it in the future. I wish I knew about the MMs before I wasted money on the 38120s. I also wasted money on the BMS boards and all the other stuff. Oh well you live you learn.

 

[Dakotalee]

That's tough. I thought about building my own batteries also. I settled buying battleborn. Top quality. Quality BMS.Will last 20 years. 10 year warranty. Over spec'ed. Less hassle. Worth the extra to me. Mighty max is a solid alternative. I had their AGM batteries prior. Good American company. Thier bms is slightly cheaper. You cant parallel wire more than 3 of thier lithium.

 

[Dakotalee]

Also , I'm hearing tesla car batteries and the like might be a cheaper alternative. If you can keep up with the more technical side, which sounds like you can.i havent looked into it much past seeing other hobbyist builds.

 

[jacqueg]

I'm no help at all. But this guy might be - 

 

[B and C]

Wiring batteries in series multiplies the voltage by number of batteries.
Wiring batteries in parallel multiplies the Ah by number of batteries.

Your 4 batteries in series is 12.8 VDC at 8 Ah
Four series sets in parallel will be 32 Ah

Your two 10 Ah ones skew things a little. Doing what you are doing, I would only use matched capacity cells but that is me.

 

[izifaddag]

Well the math got corrected much earlier in this thread but thanks anyway.
Using 38120s seemed like a really good idea at the time. However once I learned about the Mighty Max I was done. The price has gone up now to $675 but it is so much easier. No more elaborate wiring or fiddling around with BMS boards. I am just about to order my first one. I will review when it arrives. Also using Newpowa solar panels @ 100 watts apiece. Have to see how this goes. Haven't decided on an mppt controller yet.

 

[izifaddag]

Apparently M.Max batteries can only have 4 paralleled. I do not see why there is a limit on it. You can have as many banks of 38120s as you want in parallel. Unlimited.
I do not want to waste the bank I built so I have written to M.Max to hear their opinion. I am thinking 2 separate chargers and parallel into the inverter.
My current charger is soldered right to a dedicated negative i/p pad on the BMS. It controls the balancing of the 4 cell banks by limiting current flowing through the negative lines on all the banks of batteries.
The MM has just 2 terminals like an ordinary car battery. I am not sure how this is going to work. The internal BMS must be inserted between either the positive or negative terminal to control current flow, thereby balancing the cells.
I am confused.

 

[B and C]

The mighty max batteries have the bms built into the case.

If I decide to change to Lipo4 and things remain the same in the industry, I would cry once and get battleborn's. I'd have to install a battery to battery charger, change my shore power converter and reprogram the solar charge controller. Still undecided but I do remember the samsung phone fires from a few years ago with the faulty bms. Not sure I want to risk burning down my house.

 

[jonyjoe303]

The standalone batteries like battleborn and mightymax don't work well with solar. You have to set the bulk setting on the controller low enough so it doesnt trigger the bms. When the bms bulk setting is set too low, the controller will not put out max amps.

The reason is if the battery bms decides to stops the charge your going to get voltage surges as the controller tries to keep charging the battery. I encountered voltage surges with mppt and pwm controllers, myself  I wouldn't trust any controller. One thing you can do is place a smaller 12 volt agm battery parallel with the lifepo4, if the bms trigger on the lithium, the lead acid is still in the loop and the controller won't produce voltage surges.

Yes you can parallel as many batteries as you want as long as they are the same voltage. Even the mighty max, if they each have there own bms, if one bms stops the charge the other batteries will still charge, the only problem is if all the batteries bms stop at the same time, then you get voltage surges. I parallel my 220ah lifpo4 with a 27ah 12 volt agm lead acid and left them connected all night long once the voltage equalizes nothing happens no more current flows from one battery to the other. Connecting all your lifepo4 together even if they are different amp hours, once they reach 13.1 volts they equalize and remain at that voltage. I measured amp transfer between batteries using a dc wattmeter and once they equalize very little amps are transferred from one battery to the other.

Getting the batteries connected in parallel is the easy part, the hard part is getting to charge with solar and avoiding the voltage surges. Its a learning experience but can be done.

 

[izifaddag]

The mighty max batteries have the bms built into the case.

If I decide to change to Lipo4 and things remain the same in the industry, I would cry once and get battleborn's.  I'd have to install a battery to battery charger, change my shore power converter and reprogram the solar charge controller.  Still undecided but I do remember the samsung phone fires from a few years ago with the faulty bms.  Not sure I want to risk burning down my house.

My Mighty Max has arrived. It looks impressive but that doesn't mean much I will give a report as this thing does its stuff. I honestly believe that Battleborn are no better and certainly not worth the cost. I have seen this over and over during my life where a company claims magic abilities and a cheaper brand is just as good.
A very good example is the Espar heater. These diesel heaters cost thousands. In 2014 I broke down in SLC and replaced mine. $1100 down the drain. You can buy a Chinese one on ebay for $150 and install it yourself. I have yet to see a bad review. 
Battleborn are the same. 
Victron the same.
Renogy the same.
It is not that I am criticizing the quality of their stuff. It is really good equipment but highly over priced. Beyond my pocket. I'll stick with the MM for now anyway. $675 was bad enough! 
The batteries that were catching fire were a different type of lithium battery. They use cobalt instead of phosphate. The phosphate aren't as good electrically but much safer. 
As for bulk charging from the solar I shall have to experiment with that to tailor all the settings. I am starting small so I will go slowly and just have to learn. 
This whole project just keeps getting more expensive. I will be unable to charge the battery while I am driving for now. I can't afford a DC-DC charger so that will have to wait. I also realize that my 110v to 12v charging is not going to be adequate. Again I cannot afford to buy a high end one. What I have will have to do for now and will be a learning experience. 
As I say this just keeps getting more expensive. For the minute I have decided to leave the panels unmounted. I am going to stand them against the side of the camper and run the wires to the controller. Heck if that gives a good result I might even build a folding frame and leave them like that. 
I don't have any more money to spend on mounting materials and I have run out of time and desire to do anymore work to the camper for the minute. I want to go somewhere cooler and find work. I spent all of 2019 DIYing every single day and I burned out in Feb/March 2020. Then the plague hit and the overreaction began. Been in suspended animation ever since. I need to go and re-energize. Some work and some money is what is needed now.

 

[MotorVation]

The standalone batteries like battleborn and mightymax don't work well with solar. You have to set the bulk setting on the controller low enough so it doesnt trigger the bms. When the bms bulk setting is set too low, the controller will not put out max amps.

Actually, my Battleborn's can safely accept a 50AH charge each for a total of 100AH. I have seen my charge controller pulling in 45AH and the batteries sucking up every last drop of juice. My bank was normally fully charged and out of absorption by 11:00 AM out west. Sometimes earlier.

I'm parked under a tree in my driveway here in Florida and I still manage to get out of bulk and into absorption most days. If I don't, it doesn't matter. The batteries don't have to be fully charged every cycle