So I decided to build my own 200 amp LiFePo4 battery for my van

[Deryk_the_Gypsy]

After watching a bunch of will's video's I decided to make one for my 2010 transit connect camper conversion. I ordered the cell's from here https://pt.aliexpress.com/item/4000...m=a2g0o.store_home.promoteWysiwyg_515358087.3 I purchased the BMS from OverKill Solar.

Assembly was pretty straight forward.

I have a 2010 transit connect with 150 amp alternator. I have a renogy 50 amp dc to dc charger, 7gauge wire running from the isolator and main battery to the charger.

I have the android version of his app on my phone and I am having trouble getting the battery to charge. I open the app before I start the van and the charging voltage is too often 0 amps and it will go from .1 to 40 amps but with effort after an hour drive today I am at 30%. I only changed in the settings was for it being a 200 amp battery and 160 amps useable. I will admit I am disabled and don't drive a whole lot but I have at least 5 hours of highway time and I just can't seem to get it higher. The voltage is the same, I checked the battery and compared it to the app and they are the same. Whenever the car is running it shows as the battery is either at 200 amps or 199 sometimes the center display that shows remaining watts/how long is always wrong, usually showing under 2400 but sometimes as high as 5k to go.

Yesterday when I came home from another 45 minutes on the highway for 7 hours everytime I checked the app the battery was at 100% around 8pm when I went out it showed it at 30%. 13.22 volts

Any ideas? I was planning on adding 200 watts of solar on the roof in the spring when I add a 12 volt compressor fridge but just can't seem to get the battery charged. Friday I have a 100 some mile trip and tuesday will be returning so I would like to see the battery getting topped off after 2 months.

 

[snoobler]

I don't recognize that source as one of the trusted sources.

The Renogy in the picture says 40A.

The page you linked says 135Ah not 200Ah. Unless you have massive hands, those cells look very small. They look to be about the same size as my 40Ah CALB cells.

1. What are the LxWxH measurements of your cells?
2. Is the % battery from the overkill or some other device?
3. Do you have the overkill programmed for your actual battery capacity?
4. What voltages are the charger programmed for?

Page 19:

https://www.renogy.com/content/RNG-DCC1212-60-BC/DCC1212-204060-Manual.pdf

Set set DIP switches for 14.4 and 13.5

 

[Deryk_the_Gypsy]

ok, here is the link for the batteries I purchased. I don't have great access to opening it up to measure the cells but they were tall. https://pt.aliexpress.com/item/4000325064942.html I changed the dip switches to I believe are what you suggested. I did change the settings to the app with it being a 200 amp battery with 160 useable amps. I verified the voltage of the battery with a voltmeter and it matches what the BMS from Overkill is showing.

 

[snoobler]

1. Are you using power in the intervals between 100% and 30%?
2. What are you powering?
3. Is the Overkill registering an Ah or Wh draw between those readings?

 

[Deryk_the_Gypsy]

The battery isn't powering anything currently. Besides testing to make sure it works by turning on and off my maxxair fan and an overhead light. The only thing connected and using power is a 12volt propane gas detector. I went for a larger battery because my plan is to add a 12 volt compressor fridge (30 some quart size) and to be able to charge my ebikes battery for the spring.

 

[snoobler]

I see the following possibilities:

1. Faulty cells (unless you tested them individually before build)
2. Faulty BMS
3. Faulty charger
4. Faulty connections
5. Faulty configuration/installation

 

[Deryk_the_Gypsy]

I did measure the voltage of the cells when I first received them, they were all pretty close around 3.24v each. Could be the BMS, I know the charging isolator was working because it did keep a charged lead acid battery I had there till I did my electronics upgrade.

How can I verify the charger is putting out adequate voltage? Start the van and put the test leads on the pos/neg wire from the charger?

thanks

 

[snoobler]

If you have a DC clamp meter to measure current, that would be a way to verify you're actually getting output reflected on the overkill.

 

[Deryk_the_Gypsy]

Unfortunately I don't have a clamp meter, just a simple voltmeter. How else could I test it?

 

[snoobler]

If the charger is charging at 40A, you could try to measure a voltage at the (-) output of the charger along the wire to the (-) input at the battery. It will be a very very small voltage, but the fact that there's a voltage at least confirms there is current flowing. You could also check voltage at the charger output terminals and the battery terminals. The voltage at the charger should be a wee bit higher.

I would re-visit the overkill bms manual to confirm everything is connected and configured correctly. Check all connections to make sure they're not loose.

IIRC, the overkill has % SoC target points as part of the setup, and they may be mis-configured. 13.2V should be about 70%.

Also, confirm that the cells are consistently within 0.05V of each other.

 

[Deryk_the_Gypsy]

here is a screen shot of the app opened

 

[snoobler]

Nothing amiss that I can see. Great balance. It's clearly counted 140Ah used, or it wouldn't have only 60Ah left.

Have you checked all your connections and confirmed the BMS is hooked up properly?

 

[Deryk_the_Gypsy]

in this one it looks off, it says 40% setting is 3.15v and the main screen shows I am at 30% with 13.18v I haven't used the battery for anything other then checking that the lights and ventfan and water pump worked, everything is off all the time. I don't live in the van, just for weekends and holidays and there isn't any regular draw on it besides the propane sniffer and that has to be a real low draw.

 

[snoobler]

It's reporting 30% based on an available 60Ah of 200Ah (200/60 = 30%). The BMS has counted 140Ah being used.

I'm at a loss.

 

[Deryk_the_Gypsy]

I have a 2000 watt Bestek inverter, yesterday morning I removed the wires from the battery for it. It was turned off and the green led on the front of the inverter wasn't on, but I was wondering if something was taking juice away from the battery. Yesterday I emailed overkill because when I came back from a ride the display on the BMS's app showed the battery was at 100% typically a little while later it would drop down to display the real value(Most of the time while charging it would show 100% and when I went into settings it would show the battery was full,(occasionally it would show the actual percent) then a little while after shut down it would display the real values). Yesterday I got home at 1:15pm and came out hourly to check the app and took till after 8pm for the app to go back to showing 30%. I did restart my phone when it kept saying it was at 100% to see if that was the app just being buggy.

My electrical system is pretty simple, I ran 12 gauge marine tinned 12 volt wiring for each of the 4 fuses in my fusebox, 1 to the Maxxair fan, one to my overhead led white/red light, one to my water pump(and that is always off or it would kick on and you would notice it). and one to a switched panel with a meter and 4 fast usb chargers. Now friday I am heading away out of state for a few days so i have a little over 200 miles round trip, hopefully I can get the battery charged.

 

[jony101]

When you have the engine running measure the voltage at the lifepo4 battery terminals, you should read 14.6 volts, anything less and you will never get max amps to the battery. The voltage has to be high enough to force the amps to flow into the battery.
Also check what the voltage is on the start battery, it should be at 14.4 volts, where its producing max amps. Some alternators don't run at 14.4 volts all the time due to fuel efficiency.
The lifepo4 can easily handle a 40a charge rate up to about 80 percent, then your dc charger will start reducing amps.

 

[Deryk_the_Gypsy]

Ok thanks, tomorrow I will check it and let you know!

 

[Deryk_the_Gypsy]

Raining of course but I started the van and tested the voltage at the battery and it was around 14.3v the idle was under 1500rpm's and its a 150 amp alternator I have a meter for the van's main battery and it usually shows 14.2 to 14.4 when I plug it in(part of a bluetooth unit for the radio. So it looks like battery is getting voltage from the dc to dc charger

 

[jony101]

on the renogy, you have the dip switches set for 14.4 volts, if you move s1 down you will be at 14.6 volts. 14.6 volts would be better for lifepo4, its what I use for my 220ah lifepo4 battery. If there is any voltage drop from the renogy to the battery that extra .2 volts will help. Also on the overkill, single voltage full, its at 3.4 volts, I would move that to 3.65 volts(which is the max for lifepo4). When you want to fast charge your lifepo4, you always want to have all the parameters at the max.
One thing that happens when the overvoltage full is at 3.4 volts, the bms will stop the charge as soon as a cell reaches that voltage. When charging at high amps, it would be very easy for a cell to reach voltage quickly.
One thing I notice when charging my lifepo4 at high amps, one of the cells always reaches the cutoff before the rest. Even if the battery seems to be in perfect balance at the lower voltage, once charging they start to drift. that might be happening in your situation. When charging, use the bluetooth to see the 4 cells voltage as they are being charge, if one is higher then the rest that might be your problem. I use the qnbbm balancers on my 4s lifepo4 battery because without them I could never get a full charge.
You can try charging at a lower rate maybe 10 amps or 20 amps to see if that helps. A battery that has balance problems will not fully charge at high amps, the bms will always stop the charge early.

These are the active balancers I had to use on my 4s pack. Without these one cell was always reading .20 volt more then the rest.

 

[Deryk_the_Gypsy]

well I am ok with not bringing it up to 100% full, I heard around 90% is better for extended cycles. When Will P. talked about it on Youtube, I took it into consideration and originally was looking at around a 150amp battery planned for using 80% then thought about the 200 amp cell's were on sale and when it eventually loses capacity, it's still a big enough battery to still be good for keeping a 12 volt fridge going for an extra 2 or 3 days. I guess when I get back from the 200 + mile trip will see how much juice gets pushed into the battery. I did change dip 1 like you said for the extra .2 volts... could always change it back if I want. The drive should be enough to mostly charge it if everything is working right...i hope lol