Battery capacity

[peerjay56]

Any way to check the remaining capacity in a used phylion battery?
Not currently fitted to a bike, and don't have another one to fit it to.

 

[Geebee]

Discharge it through a load ie 36v 3x 12 globes in series whilst monitoring the current to work out the Ah and the voltage to prevent going to low.
You could just use the wattage of the globes as a guide for discharge, or for a crude idea discharge to say 34v and then time the charge and workout how many Ah were put back in by the charge current.

 

[trex]

charge it to full, then discharge it through a load like geebee said. The three 12V 50W bulbs in series should burn about 120W - watch how long it takes to dim.
If you are brave, leave it until the battery reaches LVC, the BMS should switch the lights out.
Then charge up to full. You can measure how much power is consumed by the charger with an energy meter. Multiply the consumption by 0.9 gives you the battery capacity.

 

[D C]

I take it that it wouldn't temporarily fit your Cyclotricity kit, I'm sure you've thought of this.

 

[peerjay56]

I take it that it wouldn't temporarily fit your Cyclotricity kit, I'm sure you've thought of this.

I did, DC, but I'd have to bodge it, and it would only give me a subjective answer. I was hoping for a more definitive result

 

[D C]

I did, DC, but I'd have to bodge it, and it would only give me a subjective answer. I was hoping for a more definitive result

Thought so, silly of me to ask

 

[peerjay56]

Thought so, silly of me to ask

Not at all. Never assume I know what I'm doing:S

 

[Deleted member 4366]

The only way to know is to connect a known load and time it. Watts x hours = watt-hours.I should have about 360 wH. Other than that, you can get a cheap watt-meter, clamp the motor in a vice and run it without load. It should last 10 to 12 hours. Whatever test you do, keep a voltmeter on the battery to see what's happening. It should give a good prediction of when it will cutoff.

 

[jhruk]

A battery tester is always handy and need not be expensive. Here's my set-up using an old fire bar as a load and a cheap watt-meter.

The load can be adjusted by moving the crocodile clip along the bar – remembering that it does get hot and being careful to avoid a short! If you're going to test the battery to cut-off it's best to connect another small battery to the aux input on the watt-meter so you don't lose the reading when it cuts out.

This really didn't cost me anything as the old fire bar was scrap & I already had the wattmeters.

 

[Deleted member 4366]

Brilliant!

 

[mountainsport]

A battery tester is always handy and need not be expensive. Here's my set-up using an old fire bar as a load and a cheap watt-meter.

The load can be adjusted by moving the crocodile clip along the bar – remembering that it does get hot and being careful to avoid a short! If you're going to test the battery to cut-off it's best to connect another small battery to the aux input on the watt-meter so you don't lose the reading when it cuts out.

This really didn't cost me anything as the old fire bar was scrap & I already had the wattmeters.

Fantastic jhruk I am intrigued, even though I still don't know what's going on here.

MS.

 

[peerjay56]

charge it to full, then discharge it through a load like geebee said. The three 12V 50W bulbs in series should burn about 120W - watch how long it takes to dim.
If you are brave, leave it until the battery reaches LVC, the BMS should switch the lights out.

OK. Tested the battery, (thanks to Geebee for method). I would be grateful if someone would check my working!
Start v = 41.6 time = 09:00
End v = 31.5 LVC (bms cutout) time = 11:40 total time = 2.6 hours
Current = 4A continuous
Load = 6x12v 25w bulbs; 2 parallel banks of 3 in series (i.e. to replicate 3x50w in series)

At start of process, load = 41.6v x 4A = 166.4w
At end of process, load = 31.5v x 4A = 126w
Average load = 146.2w, x 2.6 hours = 380wH

Watts x hours = watt-hours.It should have about 360 wH.

That 380wH seems too high? Have I forgotten to take something into account? From D8veh's figures, I'd expected a 'burn time' of about 3 hours. So is 2 hours 40 minutes to LVC OK or not?
Using Trex's 120w as the average brings it out at about 312wH.
Comments/observations gratefully received.

 

[Deleted member 4366]

The bulbs are only approximately 25w. There's a degree of error on every measuring device, so your results will only ever be approximate, but from what you've done, I'd declare that battery a good'n

Where did you get the figure of 4 amps from. I'd expect the current to change with the voltage, since the resistance of the bulbs stays approximately the same:

Assume that they're exactly 25w at 12v. At 36v, the current would be 4.17 amps, at 41.6v it would be 4.74 amps, and at 31.5v, 3.65 amps. The voltage sags under load, so the actual currents would be about 5% less.

The only sure way is to measure with an accurate wattmeter, but it's academic. The main thing is that there's enough energy in the battery to do a fair distance.

 

[peerjay56]

The bulbs are only approximately 25w. There's a degree of error on every measuring device, so your results will only ever be approximate, but from what you've done, I'd declare that battery a good'n

Where did you get the figure of 4 amps from. I'd expect the current to change with the voltage, since the resistance of the bulbs stays approximately the same:

Assume that they're exactly 25w at 12v. At 36v, the current would be 4.17 amps, at 41.6v it would be 4.74 amps, and at 31.5v, 3.65 amps. The voltage sags under load, so the actual currents would be about 5% less.

The only sure way is to measure with an accurate wattmeter, but it's academic. The main thing is that there's enough energy in the battery to do a fair distance.

Thanks Dave.
I measured the current with an analogue multimeter at the start, and then again after LVC (after the battery had rested for a couple of minutes). I realised it was an approximation, but thought the drain would stay relatively constant. Not my forte, electrickery, so thanks to all who contributed.

 

[mumbles]

Hey Guys,

Isn't 380wH higher than the rated capacity on the battery? I understand that manufacturers often pack batteries to label + say 10% so they always hit their stated capacity, and the capacity test isn't an exact science, but I would of thought the battery would be hitting around 320wH.

Think dave has already answered the query really, with the sag in voltage. The continuous current is a bit confusing with the drop in voltage?

Any way sounds like its sound to me if it ran those bulbs for a decent amount of time.

Cheers.