Battery charging is less than capacity of battery?

Chris456345234 · Apr 3, 2017

I got a 48v battery with 10ah. If I run it dead and charge it with a kill-a-watt it tells me it pulled about 0.25 to 0.31 kwh. Shouldn't a 48v x 10Ah = 0.48 khw capacity?

If anything shouldn't the kill-a-watt always show over 0.48 kwh as it takes more energy to charge the battery?

flat tire · Apr 3, 2017

Are you running a cycle analyst to tell you how much power you're discharging?

If not I'd imagine you've just learned that actual capacity can be less than nominal. Without any other information provided I would guess this is from using a cheap Chinese battery with no-name cells and / or maybe your pack is just old and the reduced capacity is normal.

Chris456345234 · Apr 3, 2017

I do not have a cycle analyst. This is a li-on battery that came with the bike. It's one year old, and it used to give me about 35km+ when fully charged. On Saturday it died at 13km (also gave me a low voltage error). There is only 630KM on this battery (probably under 50 charges) and I have taken good care of it. It has only been run dry ~4 times.

I am going to bring it into the shop in a few days to see what they say. It seems hard to believe the capacity would be diminished so much. I am hoping its something simple like some of the cells went bed which is causing the bike to fail due to low voltage.

flat tire · Apr 3, 2017

Sounds like you have a no-name Chinese pack. It's expensive, but the only way to get a reliable battery pack with good lifetime is to get one that uses high quality cells like Samsung 25R, 30Q, LG HG2, Sony VTC4...

tomjasz · Apr 3, 2017

Measure your starting voltage after a charge. Then your ending voltage. Are you charging to 100% 54.6V? Or less to conserve the battery life?
I trust my multimeter first.
Sometimes charging for 6-8 hours a few time will balance the pack and recover some. But without any real data it's hard to be very helpful.

Chris456345234 · Apr 3, 2017

I will test it with the multimeter next time I put in about 10km, but right now (after a full night charge) it's telling me 54.2 volts. I often take the charger off the battery (when the light goes green) instead of leaving it overnight (the charger turns green it still pulls in about 15w of power and decreases over time).

I kind of want to open this bugger and see what type of cells are in them. I also wonder if worse case scenario, wont I be able to order some 18650 cells and solder them into the battery (as I would save money on the case, charger, BMS and wiring).

flat tire · Apr 3, 2017

Personally, I would advise against that unless you get the batteries for very cheap or free (see below) although many people have done it. First, soldering 18650s kind of sucks unless you have a high wattage iron and additional protection for the top transition area where the battery goes from positive tip to negative casing.

Second, you're putting money into a black hole that goes nowhere. Save that money, get a battery made of good cells, and you will have a battery that provides near the advertised capacity for a really long time AND doesn't voltage sag like a mofo.

999zip999 · Apr 3, 2017

Very bad to run battery to cutoff as a rule. Very bad. Plus more info on your bike. Where you get it a link some pics. Info. Lots.

cassschr1 · Apr 3, 2017

Leave the charger on it.
ride a couple km.
charge again, ride a bit, not alot.
charge again. Leave charger on it 24/48 hrs, aint gonna hurt it. I was surprised how many ah my pack picked up.

amberwolf · Apr 7, 2017

Chris456345234 said:
but right now (after a full night charge) it's telling me 54.2 volts. I often take the charger off the battery (when the light goes green) instead of leaving it overnight (the charger turns green it still pulls in about 15w of power and decreases over time).

This is because it is balancing the cells.

This can take hours ot days to weeks depending on how out of balance they are.

The more often a cheaply-made pack is run down to empty the more likely it is to become unbalanced, and when run down to empty while unbalanced the worse the unbalance itself becomes.

Try leaving it on the charger all the time you are not using it, and charge it at the destination as well as at home (again, leaving it on the charger all the time it is not in use).

markz · Apr 25, 2017

If there is lots of voltage sag that means you have less parallel groups of cells.
I wonder though when you have that voltage sag, if Ah then decreases much?

amberwolf · Apr 25, 2017

If you have a BMS or controller that cuts off because of that sag, then yes.

Otherwise...it depends on teh cells how much of a problem that is. Some are worse than others for their Peukert effect losses.

Battery charging is less than capacity of battery?

Chris456345234

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flat tire

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Chris456345234

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flat tire

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tomjasz

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Chris456345234

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flat tire

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999zip999

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cassschr1

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amberwolf

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markz

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