Generic LiFePo Battery Question......

[Bruce]

@Bruce Just sent the order for two of these batteries and the charger you linked. Should be here this week. I'll keep you posted on how they work out.

Thanks again for the help testing!

We took Gavin’s battery pack for spring break in New Orleans. Lots of walking and he never got below 60% of the combined batteries. I also was able to use two chargers at the same time reducing the time to charge.

Thanks for posting. These batteries were faster, easier and less expensive than the pack I would have built out of 21700s.

 

[2kwik4u]

We took Gavin’s battery pack for spring break in New Orleans. Lots of walking and he never got below 60% of the combined batteries. I also was able to use two chargers at the same time reducing the time to charge.

Thanks for posting. These batteries were faster, easier and less expensive than the pack I would have built out of 21700s.

View attachment 196444

View attachment 196445

Man, Thats cool. I'm glad it helped out. Looks like the group had a good time!

 

[2kwik4u]

@Bruce

Got the new batteries in yesterday. ATV ran like a champ for about 15-20 minutes. Now it shuts down after about 3 seconds of power. We were grilling out so I didn't have time to troubleshoot, however I have some thoughts.

Either the controllers protection circuits are protecting it from something, OR, the battery just died, and the internal BMS systems are keeping it from overly discharging. I haven't ran a voltmeter across the leads yet, or anything else. I also didn't charge the batteries before letting the little one loose to ride it, so I'm thinking they might just need a charge. Do LiFePO4 batteries behave this way? Feels like full power, then nothing. Like, not even enough to turn on the indicator LED's. Think I just need to put a charge on them?

Speaking of chargers. The new charger doesn't fit the old plug. SO, I had to move the old plug to the new charger. Not terribly difficult, I found positive and negative off the old charger, and the new charger only uses 2/3 of the pins, so I figure it works the same way. Stripped/soldered/heatshrank the leads, but haven't plugged it in yet. Anything I need to be on the lookout for there? I was initially worried about power draw across the wires, but the old plug had larger conductors than the new plug. Old charger did 24V at 1.5A, new charger does 29.4V at 2A. Slight increase in wattage, but again, the old plug had larger conductors so I'm not terribly worried about it. Anything else I should be on the lookout for here?

Thanks in advance for the help!

Edit here's a couple pics.

New Charger on the left:


New plug on the left:


New plug with outer shell removed.


Best I can tell this should work when I plug it in. Just didn't have time to troubleshoot last night.

 

[adrianp89]

From what I am told that is how they work. You get 100% then 0%.

 

[2kwik4u]

From what I am told that is how they work. You get 100% then 0%.

Fingers crossed that's the only issue then. Thanks.

 

[Bruce]

Fingers crossed that's the only issue then. Thanks.

My memory is that the batteries came fairly discharged. I would charge them up and check the voltage. Based on my experience voltage should be around 27.5 fully charged with the charger disconnected.

Lead acid batteries without protection will continue to discharge damaging the battery. That could create a fireball with lithium batteries so protected batteries cut off at a safe voltage.

Hopefully you just ran the batteries down.

My son wanted to keep the extra batteries on his chair so they have been going to school with him. I notice that his chair which used to come home with a 50% charge still has the green lights showing a near full charge when he gets home so the extra batteries are making a difference.

Perhaps check the voltage periodically during usage to compare to this chart.

 

[2kwik4u]

My memory is that the batteries came fairly discharged. I would charge them up and check the voltage. Based on my experience voltage should be around 27.5 fully charged with the charger disconnected.

Lead acid batteries without protection will continue to discharge damaging the battery. That could create a fireball with lithium batteries so protected batteries cut off at a safe voltage.

Hopefully you just ran the batteries down.

My son wanted to keep the extra batteries on his chair so they have been going to school with him. I notice that his chair which used to come home with a 50% charge still has the green lights showing a near full charge when he gets home so the extra batteries are making a difference.

Perhaps check the voltage periodically during usage to compare to this chart.

View attachment 196995

Thanks Bruce. You rock!

I checked the voltage before installing them I didn't take a picture, but 26.1V sticks in my head. That's ~35% charged according to the chart. I'm gonna guess he rode the ATV for maybe 20min before it shut off. I'll check voltage tonight before I do anything else to it and see where I stand.

I'll keep you posted!

 

[2kwik4u]

Well @Bruce I found one of my problems. My 15yr old DVM from harbor freight was finally dieing on me. Not sure I can trust any of my data on this project at this point. I'm going to go pickup a new one tomorrow.

This happened as I was taking reading on the batteries.


With that said.....I got 13.62V on one cell, and 11.50V on the second. I don't think that 11.50 is correct, but maybe it is. I couldn't get a combined read for some reason. I'm guessing it was failing DVM issues.

I rewired and verified the charger was putting out voltage on the right pins. It immediately flipped from green to red when I plugged it in. The batteries aren't getting hot, and the magic smoke is still inside as of this writing. I'm about 3hrs into charging and it hasn't flipped to green yet. I might unplug for overnight for safety.

More details as they arise tomorrow.

 

[Bruce]

Would be concerning if one of the batteries really was 11.5V

 

[2kwik4u]

Would be concerning if one of the batteries really was 11.5V

I thought the same thing. Will report back with new DVM tonight.

Green "charged" light is on this morning.

 

[2kwik4u]

@Bruce

New DVM! Just in time too, electric oven broke today while wife was home trying to make lunch. Will give the new toy a good workout tonight.



I checked voltages
13.19 on RS
14.39 on LS
27.58 across both (in series w/40A fuse between)
29.48 from charger

Is it possible that the load isn't balancing itself here across the two 12V sources? The RS was the one I pulled the 11.5V from yesterday before getting the charger going.

This is what I have installed. It's a simple series setup.


The machine appears to be riding and operating just fine. I'll try to get some runtime vs voltage data if I can get the 5yr old off it for a few minutes.

Any thoughts?!?

 

[2kwik4u]

@Bruce

~15min of pretty consistent full throttle use brought us down to the below numbers

12.87 RS
13.25 LS
26.14 Combined

I'm pretty certain it's a 24V 400W 350W motor in there. It has two settings but only one works (not sure why), so it might be reduced power.

*edit*
It's a 350W motor

Dirt Quad - Razor

The Razor Dirt Quad brings unlimited adventure. The electric four-wheel Dirt Quad is built strong and sturdy to conquer tough trails and big bumps.

razor.com

*edit #2*

Looks like about a 2.4% drop on RS and a 7.9% drop on LS, and an 11.3% drop overall. Predicting around 180min of runtime at this rate, if I can use all 100% of battery.

 

[Bruce]

The difference in voltage between the cells worries me. I would disconnect and check their voltage separately. Ideally you would charge them separately to get to the same voltage before putting them back in series.

You may want to contact the seller about a replacement.

How do you feel about the predicted three hour runtime?

 

[2kwik4u]

The difference in voltage between the cells worries me. I would disconnect and check their voltage separately. Ideally you would charge them separately to get to the same voltage before putting them back in series.

You may want to contact the seller about a replacement.

How do you feel about the predicted three hour runtime?

I'll take them out tonight and figure out a way to charge them back up separately and see if I can "self balance" on that front. If the RS doesn't come up, I'll reach out to the vendor and see what can be done. Not 100% certain how I'll do that, as I don't have a power supply in the 14V range that would be needed to charge a single battery. Any thoughts on how to make one?

I wonder if they came in at different voltages and I just "let 'er rip" without checking and damaged one!??!

The 3hr run time would be pretty good. I'm not sure he's every put a straight 3hrs on it before. Typically he gets bored of it and moves on before it goes completely dead. We have a ~1mile loop in the field behind us. If he can do that loop with his older brother twice, then I'll call it a win. It's at least good as it was before, if I can get these to last more than a season and retain a charge it'll be a big win.....However, now that I say that, I suspect he's going to outgrow this machine by then and need an upgrade.

 

[Bruce]

I pulled my pair of batteries apart to reconfigure as 12v to run an inverter for a demonstration. Found one at 13.3V and the other at 14.3V. I am charging them separately to see there they end up.

 

[Bruce]

1/10 of an amp and few minutes brought the 13.3 volt batter up to 14.3 volts. These things are very sensitive at the top end.

 

[2kwik4u]

@Bruce

Is there a downside to that sensitivity or is it just an odd trait?

 

[Bruce]

@Bruce

Is there a downside to that sensitivity or is it just an odd trait?

I am not sure. I may run a discharge test on both batteries to see what the actual capacity is. According to the chart 13.3 volts should be 90% and 13.6 should be 100%. But that is a generic LifePO4 chart. 13.3 could be 100% for these batteries.

If you are getting the run time you need and the batteries last then these details do not matter. At the price I would expect the batteries to have very inexpensive cells inside.

 

[2kwik4u]

I am not sure. I may run a discharge test on both batteries to see what the actual capacity is. According to the chart 13.3 volts should be 90% and 13.6 should be 100%. But that is a generic LifePO4 chart. 13.3 could be 100% for these batteries.

If you are getting the run time you need and the batteries last then these details do not matter. At the price I would expect the batteries to have very inexpensive cells inside.

Well, The tike road for ~45min tonight and it died. When it dies now it just shuts off. Full power -> nothing, no in between. I assume that's the BMS doing it's thing and protecting from complete undervoltage. Of course this time it died when he was out in the middle of the field. Had to put the Q7 in "off road" mode to get to it and get it home.

I'm pretty certain one cell is dropping low, and the second one isn't getting fully utilized. Guess I need to figure out a way to charge each of them individually before putting them back in.

Any suggestions on an inexpensive single charger?

 

[Bruce]

Any suggestions on an inexpensive single charger?

This would work. https://amzn.to/3nQnb4p

I am guessing you have a bad cell.

The ISDT Q6 would work as well and allow testing discharge but it needs a power supply to power it. I am using an old 12V 5A power supply that I had laying around. Hooking it up to your car battery would be fine.

The fastest, least expensive option would be a pair of wires and alligator clips to parallel the battery that is low to your car battery while the car is running. That should get it up to at least 13.6.