10Ah IN, 7Ah OUT?

rg12 · Feb 19, 2017

Hey Guys,

My 10Ah 21S LiPo charges for exactly 4 hours from empty to full with a 2.5A charger (no BMS on the pack).
I get the controller to low voltage cut off (a Greentime 72v controller) when my watt meter shows about 7 amp hours used (the pack is two years old (Zippy's)).

How come it puts out 7 amp hours and charges 2.5 amps each hour for 4 hours? it doesn't add up.

Ypedal · Feb 19, 2017

It does not charge at exactly 2.5 amps continuously... once the cells reach the end voltages, the Amps drop.. until they hit zero... this makes it slower .. and takes longer to fully charge.

30% drop of capacity with zippys after 2 years. .typical .. but time to manually check cell voltages very carefully if you do full capacity cycles.. never do full capacity cycles.

nutnspecial · Feb 19, 2017

That's true even without balancing function, my bulk does the same thing. However that's a big discrepancy. Just like a construction accuracy issue from using two different measuring tapes (yes, seriously lol), your other mentioned issue with a questionable meter reading the used AH might be alot of this.

rg12 · Feb 19, 2017

I'm checking balance constantly, all good.
Still don't know what is true anymore, I have two meters and both don't seem right...

999zip999 · Feb 19, 2017

Im also having meter problems. I have 5 thee different ones. All malfunctioning.

rg12 · Feb 19, 2017

Just found my old 100V 100A meter which always worked great and it was insync with my 60v one which was always reliable...seems that the new one that isn't accurate is showing lower amps when pulling high amps...
If I pull 200w for a minute or two, the new (non accurate one) is accurate just like the old reliable one, but when I pull about 50A+ it collects the Ah number slower than the rest.

Joachim · Feb 19, 2017

watt meter shows 7Ah...so you lost 3Ah on discharge heat :lol:

spinningmagnets · Feb 19, 2017

Some guys draw 30A once in a while, and other guys draw 60A from their battery pack. The more you draw, the less Ah you will get.

So how should battery packs be rated? They are rated at a 1A drain in laboratory conditions. I know that...when you first realize that it is like being told Santa Clause doesn't exist. It is disappointing.

nutnspecial · Feb 19, 2017

Is it really that big of an impact (amp draw) when you taper it off to same LVC and the batteries don't make noticible heat from the higher discharge?

It may be the meter accuracy in this case anyway (afaict), but I was curious.

rg12 · Feb 19, 2017

spinningmagnets said:
Some guys draw 30A once in a while, and other guys draw 60A from their battery pack. The more you draw, the less Ah you will get.

So how should battery packs be rated? They are rated at a 1A drain in laboratory conditions. I know that...when you first realize that it is like being told Santa Clause doesn't exist. It is disappointing.

But when the pack was new I've had a really accurate amp meter and it showed 10Ah passed when reached the controller's LVC.
I was pulling 45A back then...so still it should be pretty accurate.

btw, anyone know an amp meter that can go up to 90v 100A that calculates amp hours? (not watt hours or anything else).
it's best if you know one that doesn't require a shunt.

How come those little 60v ones can go up to 100A without a shunt?

Ypedal · Feb 19, 2017

they all have a shunt.. no way around that.

If you get a CA, Direct Plugin type, it still uses a shunt ( of sorts ) but that shunt is within the controller's circuit... the meter just taps onto it's ends to calculate voltage drop.

Ypedal · Feb 19, 2017

when you hit LVC, are all the cells at 3.0v ?.. or is one group dropping out first .

Joachim · Feb 19, 2017

3.0v for a lipo not to low???

rg12 · Feb 19, 2017

It cuts at about 3.3v per cell and when it does it's all balanced.

I know that there is an "inner shunt" but how come the 100A external shunt is so much bigger than the whole amp meter unit that has a "built in" 100A shunt?

Ypedal · Feb 19, 2017

the difference between something meant to be 100 amps Max vs Continuous !

Hillhater · Feb 19, 2017

rg12 said:
.
btw, anyone know an amp meter that can go up to 90v 100A that calculates amp hours? (not watt hours or anything else).
......t?

Well, if you ignor the voltage, that certainly wont be accurate for capacity .!
..As Ypedal said, your charger is NOT putting 10Ahr into the pack.!
Use the same watmeter during charging to get a better feel for input .

Gregory · Feb 19, 2017

Yes. Just stick the watt meter in between the battery and charger, and charge it up. No need to guess.

rg12 · Feb 20, 2017

Will do thanks

Would like to hear about 90v+ 100A (continues) meters that have an amp hour measuring...they all have up to 60v...

EDIT: My old 100v 100A meter that has an "inner" shunt has this part as a shunt:
http://www.digikey.com/product-deta...-llc/ACS758LCB-100B-PFF-T/620-1321-ND/2042746
and it says that it's rated for 100A (doesn't say continues or not...)
Can that thing really replace a huge and heavy 100A external shunt?

10Ah IN, 7Ah OUT?

rg12

100 kW

Ypedal

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nutnspecial

10 MW

rg12

100 kW

999zip999

100 TW

rg12

100 kW

Joachim

1 kW

spinningmagnets

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nutnspecial

10 MW

rg12

100 kW

Ypedal

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Ypedal

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Joachim

1 kW

rg12

100 kW

Ypedal

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Hillhater

100 TW

Gregory

100 kW

rg12

100 kW

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