Voltage drop under load

[underdog]

I am sorry, but I could not find exacly what I was searching for (although the info might probably exist somewhere)...

I belive I have a problem with the voltage dropping to low under load. Full battery shows 54,5v when I put it in my controller connected to a voltmeter in the middle of the cable. When I pull the throttle, it drops under 40v. And after about 3-4 km of riding, it drops from 52-51ish volts to way under 48v.

Is this normal? The reason I am asking is because my motor starts to stopp and start like crazy after a little while. it puls and stopps about 5-6 times a second, and does not pull at all really... (normal?)

Thanks for all replys (except harassing stuff....)

Regards Magnus

 

[dogman dan]

Do you have some typo's for voltages in that post? 14v of drop under load would be pretty bad, likely indicating a worn out battery.

But if you meant 54v to 50v, that's not so unusual for a still good, but getting old, lifepo4 pack.

It definitely sounds like you have a worn, or badly unbalanced battery though, based on the controller cutting out like that. It may have a 36v lvc you are hitting under load.

 

[fivari]

Another question I have before coming u wiht a diagnosis: what chemistry are you using?

 

[dogman dan]

If lifepo4, 54.5v fully charged is a bit low. Typical for a worn 16 cell lifepo4. When new and fresh, it should charge to 58-60v, then drop later overnight to 56v.

You might look at your charger, and see if it still puts out 58v. Old chargers may not put out the full voltage anymore.

If you don't leave the battery charging overnight, do that for at least a week. It may just be badly out of balance.

 

[dnmun]

54V for a fully charged 16S lifepo4 is low so you need to post up a picture of your battery and the BMS so we can show you where to measure the cell voltages. you will need to measure cell voltages while it is charging for us to have enuff info to answer any questions you have.

 

[999zip999]

A battery ? We would need a lot more info about your battery and what you are using it on.

 

[underdog]

Yes sorry.

big typo in that case.. drops 4+ volts under load (not 14v). The battery is of the Li(NiCoMn)O2 chemsitry, and it is supposed to be brand new... Has maybe 10 cycles on it...

 

[999zip999]

So you got it used ? Where did the battery come from ? V-power or bms battery or em3ev ?
Did you check the voltage output of the charger ?

 

[dnmun]

13S at 4.2V is about 54V so it is not discharged. we just don't know if it is 13S.

 

[underdog]

So you got it used ? Where did the battery come from ? V-power or bms battery or em3ev ?
Did you check the voltage output of the charger ?

I bought it New from cnebikes.com

Today it was even worse. Charged it to 54,5v yesterday evening. This morning it showed 54,2 volts. Thrashed fast down the street to work, and it showed 47v under load after 1 min of driving... Seems like it is dying FAST.

Can i be suffering from "overdrain" due to the fact that I am using a 26 amp Controller??

Specs from CNE-site:
"
* BMS(BATTERY MANAGEMENT SYSTEM) and 100V~240VAC 50/60Hz 1.8A Universal Charger Included
* Weight: 5.2Kgs
* Capacities: 48V/10AH
* Max Discharge Current: 40A
* Max Continuous Discharge Current: 20A
* Charging Cycles: >800 times
* Reference Ranges(full electric mode): 40Km
* Dimensions: 325mm L × 150 mm W × 84 mm H
"

 

[dogman dan]

Ok, it's a pretty small battery. Do you have a pretty small motor? If you have a 20-25 amps controller, I think you are thrashing it.

4v voltage drop under load would be plausible for a battery that is fine, but getting worked pretty hard.

Once it hit 47v under load, what was the voltage when resting?

 

[underdog]

Ok, it's a pretty small battery. Do you have a pretty small motor? If you have a 20-25 amps controller, I think you are thrashing it.

4v voltage drop under load would be plausible for a battery that is fine, but getting worked pretty hard.

Once it hit 47v under load, what was the voltage when resting?

Voltage when resting was just above 52v.

Im starting to think a downgrade to a 22a Controller might be the best solution(?)

 

[999zip999]

What motor ? Do you have a lot of hills ?

 

[underdog]

What motor ? Do you have a lot of hills ?

500w china-motor. gearless rear hub... (No heat issues) Not to many hills, but I dont pedal that much..

 

[fivari]

So you got it used ? Where did the battery come from ? V-power or bms battery or em3ev ?
Did you check the voltage output of the charger ?

I bought it New from cnebikes.com

Today it was even worse. Charged it to 54,5v yesterday evening. This morning it showed 54,2 volts. Thrashed fast down the street to work, and it showed 47v under load after 1 min of driving... Seems like it is dying FAST.

Can i be suffering from "overdrain" due to the fact that I am using a 26 amp Controller??

Specs from CNE-site:
"
* BMS(BATTERY MANAGEMENT SYSTEM) and 100V~240VAC 50/60Hz 1.8A Universal Charger Included
* Weight: 5.2Kgs
* Capacities: 48V/10AH
* Max Discharge Current: 40A
* Max Continuous Discharge Current: 20A
* Charging Cycles: >800 times
* Reference Ranges(full electric mode): 40Km
* Dimensions: 325mm L × 150 mm W × 84 mm H
"

Looking at the specifications, the voltage sag of 7V is not too good, but not extremely bad either. You are going far beyond the recommended continuous amperage at 2,5C. According to me the voltage sag is only due to internal resistance. The IR of your pack, cables and connections included, is about 0,27 Ohm. Let us suppose that you have a 13s4p Lipo configuration. That would mean cells with 80 mOhm IR max. Sounds high but not impossible. More important: how about the capacity?
For your information: I have a 48V 30Ah LiFePO4 battery pack myself for a 40A controller in my scooter. After 1 km, the voltage without load drops to 53V. Surface load is gone, cell voltage is 3.3V. Voltage sag under load is about 4V (from 53V down to 49V).

 

[iperov]

bcuz you need use lipo nanotech
no voltage drop

xD

 

[dogman dan]

For a 10 ah pack, a downgrade to a 15 amps controller would be ideal.

I had a feeling you were doing something that was murdering that battery. A 26 amps controller will need either more size, or a better discharge rate battery. Not really your fault though, since the battery specs are, well lets just say optimistic.

Since you have only a 2.5v drop from fully? charged, your main problem is too much amps for the battery. The battery isn't wrecked. But it will be really soon.

 

[dogman dan]

I'm still a bit confused about your charging voltage. It makes sense only for a 13s limn. 14s would charge to about 57v.

This gets to be a bit of a problem for us, maybe you have a 13s battery, and all is normal, except for you have way too big a controller for it. But if you have a 14s battery, you are not even close to fully charged.

Looking at the website, I could find nothing that would indicate what your charger voltage should be. Ask them, it's possible you should have a charger putting out 57v, but yours only puts out 54.5. Once I had a 36v charger that only put out 18v.

And get a smaller controller to use a 10 ah battery.