Advice on my house battery setup?

jyeager

New member
I would like to have some knowledgeable people review and comment about my battery idea, since I'm brand new to this.

I have 2 batches of these coming: https://www.ebay.com/itm/100-LITHIU...d=272606783733&_trksid=p2060778.c100290.m3507

They are Lithium-Ion (LI-CO) each of them is protected (onboard bms).
(reiterate, I have 200 of the cells coming)

I plan to combine them in to a 4S50p configuration and use them as a house battery in my vehicle.

I would like to have them charged via alternator and solar.

I will get an appropriate solar charge controller, so my concerns come mainly with the alternator option. It would be nice to just be able to use a simple VSR to join the house battery and starting battery when the vehicle is running. The VSR would be dumb and only join then when voltage is over 13v but would then stay connected for potentially very long periods of time pushing alternator voltage.
I can check, but I assume my alternator output will usually be below 14v.

What I have googled says that the nominal voltage should be 3.6v x 4 = 14.4v as I'm planning to go (4s).
And the max charging voltage should be 4.2v x 4 = 16.8 which my alternator would never exceed. But even if it did for a short period of time, wouldn't the batteries be safe due to their included protection (onboard BMS)?

And the batteries would be fine with alternator supplied voltage of <14v for indefinite periods of time, right?

I know the alternator would probably never fully charge the battery since that would take 14.4v at a minimum (theoretically), but the solar system can finish the charge if I am not happy with a less than complete charge.

What do I not understand fully or correctly that will cause this not to be a good idea?

Thanks.
 

Joe917

Explorer
16.8 volts is your charging voltage, your alternator will not come close. Your best bet is a battery to battery charger with a Lithium ion program.
16.8 volts is also pretty high for a 12 volt nominal system, you may want to check your 12v equipment, some of it may need to be disconnected during charging. That would be a PITA with solar.
Your Christmas holidays are going to be spent connecting wires.
 

Rando

Explorer
I see several issues with this plan:

1. You can't charge these from your alternator, as their resting voltage is above what your alternator outputs, and their charge voltage is way above your alternator output.
2. I would be worried about whatever house loads you are running from these, particularly while charging - 12V devices might not like 16V.
3. Your VSR will never disconnect as the lithium battery will pull the lead acid up to 14.4V, and your lithiums will end up overcharging your lead acid starting batteries as they will be floating them at 14.4V.
4. You can't charge these at any substantial rate (ie > 0.05C) when they are below freezing, so hope you live in Florida.

Honestly, this is not worth the effort. If you want to DIY a lithium battery, you need LiFePO4 cells which are much safer and 3.2V nominal per cell.
 

jonyjoe101

Adventurer
car alternator will put out 14.4 volts, battery wont be overcharged. But I would have a coulomb meter just to make sure your not putting more amps then you took out.
TK15 High Precision LiFePO/Lithium/Lead Acid Battery Tester Coulomb Counter 50A (this one cost 23 dollars, they got ones to handle more amps)

When you build your pack, it will be a 4s battery pack and you will need one large 4S BMS, and all 4 rows of batteries will be hooked up to this BMS. This BMS has to handle the output of your alternator, just make sure you get the correct one, some are li-ion 3.6/3.7 volt (what you need), and some are life 3.2 volts. Even though each battery has its own bms (when connected in a battery pack they will trigger only if the entire group/row of cells goes under/over voltage), you will be charging them in series and each group/row has to be monitor for balance. There are cheap 4s BMS that can handle 100 amps discharge for under 10 dollars but they might only charge at 10 amps, you need to find the right one for your battery pack.

When you are charging at high amps, its very important to monitor the balancing. One row of batteries might go up higher in voltage then the rest. A 3in1 LCD lipo balance tester (about 10 dollars) will come in handy here. You can see individual voltage and overall voltage. You always wants to know the balance status, I never rely on the BMS to handle everything.
3in1.jpg


As long as you monitor the balance/voltage of your battery pack you will be good to go. The only thing I see is you will probably never fully charge the battery. Maybe 60/70 percent but under charging wont damage it.

At Endless Sphere Electric Vehicle and Technology Forum, all they talk about is building/charging lithium battery packs, and I seen battery packs build with your type of cells. They might have more ideas there on how to put it together.
 

Rando

Explorer
Depending on your vehicle, the alternator may or may not put out 14.4V. Most modern ECU controlled alternators will very quickly drop their output voltage down to about 13.7V - 13.9V. But even at 14.4V (3.6V, per cell) you really won't be charging your battery. Here is the capacity of a 60mAH lithium battery charged to various per cell voltages. The point is that even at 3.7V/cell (14.8V for your pack) you can only charge the battery to about 10% SOC.
li-charge-voltage.png


Source: https://www.powerstream.com/lithium-ion-charge-voltage.htm

Yes you can build a large pack out of these cells, but it will in no way be compatible with a 12V vehicle electrical system.
 

rruff

Explorer
What do I not understand fully or correctly that will cause this not to be a good idea?

I don't think it's a good idea. These types of cells are not very good for the application (wrong voltage, not very safe), and the cost per W-hr is high compared to LiFePO4 cells that you can buy on ebay.
 

jonyjoe101

Adventurer
the other option is to make a 3s 11.1 volt battery pack. Thats what all the goal zero lithiums are. I made a 94ah li-ion 3s battery pack with 168 laptop batteries. The 3s battery pack even though the voltage is lower ran everything my lead acid ran, never had an inverter kick off from low voltage.

But for a 3s you have to have a very good BMS and also an overvoltage shutoff relay. The safest way to charge them would be with a balance charger, you can find some of these balance chargers for 100 dollars that can charge at 25 amps. These balance chargers are DC, so you can connect to your car battery when alternator is running. It doesnt get any safer than using a balance charger.

You already got the batteries coming, you can figure something out, before you get them.

Also get a low/high voltage alarm. I like this tenergy model because it has a very bright light and it will sound the alarm if the voltage exceeds 4.2 volts. Some cheaper brands alarms only sound when the voltage goes too low. a tenergy alarm.jpg

my 3s 94 ah 11.1 volt li-ion battery pack (168 laptop cells) , a comparable goal zero lithium would be 1000 dollars.
b lithium 168 cells.jpg

exterior of battery, weighs about 25 pounds. A comparable lead acid would be over 100 pounds.
b liion inside container.jpg
 

jyeager

New member
Thanks for the advice.

I will consider the 3S arrangement. I would then certainly need overcharge protection. Could also use a step-up converter if I needed 12+ volts out of it.

Perhaps I can include a 12v DC balance charger. Have a VSR connect alternator voltage to the balance charger when vehicle is running.
That could charge the batteries fully from 14 volts, I'm sure.

Also, for the 16 output volts, a DC to DC converter could step that down to 12.8 for distribution to devices.

Does any of this sound good? Or bad? ;)

I appreciate your help!
 

jonyjoe101

Adventurer
your idea sounds good, dc balance charger will easily crank up the voltage to fully fast charge a 4s battery pack. It takes the 14 volts from your alternator and boost it up to the 16 volts you need and there is no chance to overcharge your battery pack.

Your battery pack will be under 50 ah so it wont take long to charge back up unless you drain it all the way down.

My DC balance charger (isdt q6) maxes out at 14 amps, but I usually charge at 10 amps. At 10 amps, the amps goes up and down during charging as the charger keeps checking the battery voltage. It will stay at 10 amps charge rate until one of the cells reaches its max voltage, then the amps comes down to about 1 amp as it balances the remainder of the cells. Its extremely safe way to fully charge lipos. Anyone who builds lipo battery packs, needs to have one. Its the only way to fully test a battery pack.

And its a good idea to have a dc converter to take down the voltage from 16 volts to your devices. I start burning out fans/pumps when voltage goes over 15 volts.

balance charger isdt q6 paid 49 dollars, fits in the palm of your hand, maxes out at 14 amps.
a isdt q6.jpg
 

Rando

Explorer
You certainly could make this work, using a 3 series pack and a DC-DC converter to step the voltage up to 12.x volts and a DC-DC balance charger. However this would raise the question of why? You will end up with a very complicated cobbled together 40Ah battery with limited charge/discharge rates. For about the same money you could easily purchase a stand alone drop in LiFePO4 battery, or for even less money you could DIY a much more appropriate LFP 50Ah pack using these:
https://www.ebay.com/itm/NEW-Box-of...374341?hash=item51efabf285:g:40UAAOSwaSZaAilo

I applaud the DIY instinct (I built a 150Ah LiFePO4 pack for my camper) but I hate to think of spending more money (and lots of time) trying to shoehorn the wrong batteries into this application.
 

jonyjoe101

Adventurer
However this would raise the question of why?

before you build larger lithium battery packs everyone needs to start small. Small lithium battery pack would be just as good as a much larger battery and will provide usable power. Putting it together and getting it to work will be a good learning experience.
 

vartz04

Adventurer
They sell these for golf carts now should be able to just switch some things around and get 12v nominal and then know it’ll work
 

jyeager

New member
You certainly could make this work, using a 3 series pack and a DC-DC converter to step the voltage up to 12.x volts and a DC-DC balance charger. However this would raise the question of why? You will end up with a very complicated cobbled together 40Ah battery with limited charge/discharge rates. For about the same money you could easily purchase a stand alone drop in LiFePO4 battery, or for even less money you could DIY a much more appropriate LFP 50Ah pack using these:
https://www.ebay.com/itm/NEW-Box-of...374341?hash=item51efabf285:g:40UAAOSwaSZaAilo

I applaud the DIY instinct (I built a 150Ah LiFePO4 pack for my camper) but I hate to think of spending more money (and lots of time) trying to shoehorn the wrong batteries into this application.

Thanks for this advice. Using LiFePO4 does sound like a better idea. Maybe I will pivot and build these batteries in to a portable power pack and then work on the house system with LiFePO4.
 

jyeager

New member
JonyJoe, thanks for the advice and that charger recommendation.

If I use something like this balance charging circuit board: https://www.amazon.com/gp/product/B072F33CJW/ref=ox_sc_act_title_1?smid=A38N3TNH1N2LMX&psc=1

I should just need a reliable voltage source to charge it (moving on now to my idea of a portable power station).
Not sure how this circuit board works...do I need to provide any old 12v input and the circuit board does the rest? Or does it need to be the appropriate 16.4 volts and the circuit board just protects and balances?

My guess is that I still need a charger for the correct voltage input. In this case, could I use a step-up converter with any old 12v power supply to input 16.4 to the BMS circuit?

I can pack this all in a pelican case and have a handy accessory and learn along the way.

Thanks to all who have offered advice so far.
 

Rando

Explorer
Thanks for this advice. Using LiFePO4 does sound like a better idea. Maybe I will pivot and build these batteries in to a portable power pack and then work on the house system with LiFePO4.

Sounds like a good plan - buy one of those cheap HF knock of pelican cases and make a cool Goalzero like power pack. Just don't expect it to replace a house battery.
 

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