Cheap battery monitor

[terry2]

It just means it measures power in and out. Theres lots of things that can do that.
Everything else it does, all those dozens of protection settings are useless. They just stop you in your tracks as you try to get home, climb a curb, etc. So once you have broke down a few time and set them to values that dont interfere with what you are doing then they may as well not exist. Saves you setting them out of the way!

And as usual the BMS cut off early when he charged due to a cell being over voltage. The voltage rose faster on a full cell than the BMS could control. So it shut off. Leaving the pack quite wildly unbalanced with the lowest cell there around 2/3rds discharged AFTER suposedly charging. And he thinks that its good! All the subsequent testing shows the lowest cell just over 3.1V so pretty dead. And the rest full to partly charged. And sounds as if he is going to have an orgasm. Stop watching money making utube "experts"...

If used ONLY as a battery monitor then its OK. But you will only use it for a few days before you figure out its not needed. The PL8 and a big pack fixes all the issues, without the fire hazzard full of mosfets waiting to fail shorted, and nest of wires to light up like an electric fire... Its a pretty interface, and most of it does stuff we dont want.

On a solar system, its a nessasary evil. But in a chair its basically 3 things.
1. a cell protection system that we certainly dont need or want. Unless you want it to cut in as you try to get on a train ramp.../hill/whatever.
2. a very bad charging solution for those with dumb chargers.
3. a battery meter that you can get way cheaper.
4. a potential fire hazzard. Most lithium battery fires, inc LiFePO4 are traced to a failed BMS.

I am only going to use one for monitoring.
Like the one Ireving is doing.

[Burgerman]

OK. One question. What do you think it will be useful for? Other than a mosfet failing and starting a fire in your room?

To be sure it doesent stop you getting home, be sure to connect the cairs power direct to the battery and vot through the BMS...

[Irving]

OK. One question. What do you think it will be useful for? Other than a mosfet failing and starting a fire in your room?

To be sure it doesent stop you getting home, be sure to connect the cairs power direct to the battery and vot through the BMS...

In which case you won't get Ah monitoring. As mine is only a monitor with no BMS pretensions there's no risk there. Similarly, it won't stop you charging when it's too cold - but it will allow you to see what the pack temperature is so you can make that call yourself. I hope to link the Ah value/SOC to the R-Net battery gauge so you have the current value in front of you. Useful if you only charge every few days when it hits 70% SOC (ie 30% used)

[Burgerman]

Do you know how cold it needs to be to stop charging?

Minus 5 or so. Or about 22f in old money. You would find few problems in the UK. Esecially next to my bed! They are not damaged as such I dont think, just dont accept a charge.

[terry2]

OK. One question. What do you think it will be useful for? Other than a mosfet failing and starting a fire in your room?

To be sure it doesent stop you getting home, be sure to connect the cairs power direct to the battery and vot through the BMS...

In which case you won't get Ah monitoring. As mine is only a monitor with no BMS pretensions there's no risk there. Similarly, it won't stop you charging when it's too cold - but it will allow you to see what the pack temperature is so you can make that call yourself. I hope to link the Ah value/SOC to the R-Net battery gauge so you have the current value in front of you. Useful if you only charge every few days when it hits 70% SOC (ie 30% used)

This sounds much better.
Will a android app show everything?

[Irving]

Do you know how cold it needs to be to stop charging?

Minus 5 or so. Or about 22f in old money. You would find few problems in the UK. Especially next to my bed! They are not damaged as such I dont think, just dont accept a charge.

I agree, its not something i'd be concerned about. I suppose if your backup chair lived in an unheated garden shed maybe...

The most useful bit, after knowing SOC is monitoring instantaneous & average current draw v acceleration, yaw rate, etc. (Oh, forgot to mention it has an on-board IMU). I think, tho still monitoring, that there might be value (with some AI applied) in early warning of issues such as binding bearings, reduced efficiency motors/drive-train, or similar. I've already seen that actuator startup/run current has a direct relationship with noise/binding...

[Burgerman]

Even a shed keeps it a bit warmer than the outside. I have seen nothing here below zero at all this year so far. And even where there is, its only fleeting, and unlikely that the thermal mass of battery will reach that. Of course if you live up a mountain up north, and leave it outdoors... I live by the sea, sea level. Always a bit warmer. Even then, a little common sense or a shed will sort it.

Of course some live in colder places. I actually store my hobby lipo packs at 2c in the fridge. at 50% charge. Stops them swelling.

[foghornleghorn]

By the sea always sees less extreme temperatures than inland. During the summer you won't get as hot and during the winter you won't get as cold.

[foghornleghorn]

Forgot why I came in this thread

I have been using a 4 digit voltmeter on my LiFePO4 pack. I know roughly how much fuel I have left by the voltage, and can see when it definitely needs charging by what it drops to when going up a steep hill.

[Yennek]

Follow-up regarding my concerns about the accuracy of the meter I used. Set it up so I could measure the amount removed from the pack using the PL8. Discharged from full down to 2.9v with the internal 100w load. PL8 reported 45.336Ah discharged (from a nominal 45Ah pack). The meter reported 44.483Ah discharged. So that's what, about 2% error? (assuming the PL8 is perfect). Not terrible I guess. But it was also a really easy waveform to measure. I wonder how accurate it is with the spikes and such one sees in real life.

I installed this one on my wife's powerchair when I did the lithium conversion due to her range anxiety based on the lead acid batteries.

https://www.amazon.com/gp/product/B07D37P5KK

Yes it's shunt but at the time I couldn't find a hall version that seemed to work. It's accurate enough, but not perfect. If I compare the consumption recorded on the meter vs. the amount of charge the PL-8 says it put in, and it's 5-8% low. So, I adjusted the "capacity" setting in the meter down that amount so when she sees the %, the percent is a little conservative.