Weird power cut off

[myosis]

Hi,

Whenever i pull up to hard, (or go harder then 55km) something will cut me off. "power loss".
Sometimes it comes back on, but most of the time i have to unscrew the battery from the controller.
(because i have no kill switch yet)

If i don't sit on the bike (no load) its spins just fine.
Could it be a fault in the equipment, battery, motor, controller?

 

[Davescustom]

I think that is the battery... You need a bigger battery (more Ah) or one with higher C rate. When you push hard the battery the BMS goes in undervoltage protection.

EDIT: the cheapest way to fix the problem is going easy on the throttle.. You need to give the time to the battery recover.

 

[dogman dan]

Your battery has a bms, that it cutting off the motor before your motor ruins it. Your motor and controller is too strong for your battery. That is what is happening when you have to disconnect/reconnect. The more temporary cut offs are the controller shutting down because of low voltage. LVC, low voltage cutoff.

This may be because you chose a too small battery, or it could be because you have cells dying in your battery. Or, if you are very very lucky, you just need to leave your battery on the charger longer, so it can balance the cells. Once balanced, it may be able to handle the load, with all the cells fully charged.

But the smart money,,, is on you need a new battery. A stronger one. It can't handle the load, and voltage is dropping enough to shut you down.

 

[myosis]

Thanks!
I thought that was it..

I bought this package, the whole thing was a little shady.
http://www.aliexpress.com/item/70-100kph-speed-20-24-26-3kw-ebike-kit-3000w-electric-bike-conversion-kit-with-72v/2019863057.html
I know never buy Chinese junk, but I just had good hope not all of them where bad.

(in case you don't want to clink on the link) They promised me this:

72v 10ah lifepo4 battery
3000W
150A max discharging current,
60A continous discharging current

The battery I received was only 11 x 22 x 15 cm
waaaay smaller then he advertises. I contacted him about this, and he say they used new cells. He just couldn't tell what sort of new ones.
Are the sizes at all possible with these specs?

Guess I got screwed big time.
Does anyone know a good place to buy a similar 'replacement' battery?

 

[dogman dan]

Well, you got a monster motor there,,, but the battery is not nearly strong enough to run it. But it should pull a 40 amps controller, 10 ah headways should handle 50 amps. It could be just one cell in the pack causing the voltage drop.




It might work to run it on a much weaker 72v controller, like a 20 amps. But it may just be the battery is totally shit. I'd say invest in a good battery is your only sensible approach now, other than sell it all off for pennies on the dollar. They say it's headways in there, but maybe it's fake headways.

 

[teklektik]

The battery I received was only 11 x 22 x 15 cm
Are the sizes at all possible with these specs?

The 10Ah flat tab 38120 Headways are 38x120mm and your pack is supposed to be 24s so there is no way this has those cells. The dimension in the ad do match up for 2x (3x4) cell stacks + BMS, but as you point out, those dimensions are way bigger than yours.

They claim partial refunds if the item is not as described - which it isn't - regardless of whether it works or not. Unfortunately, this vendor has a 94% rating which doesn't inspire confidence. If I were you I'd request a refund/replacement battery+charger -- at least to get something in the pipe. Since they claim to have changed the battery from what was advertised, I'd also question the chemistry and configuration (still LiFe 24s?) just so you can at least interpret the voltages you see.

Meanwhile, leave it on the charger for a couple of days.

Then, you need to hook up a voltmeter to the battery and determine the 'fully charged' voltage and the voltage under load (most probably it's sagging very badly). Could be a bad battery or a bad charger. Unfortunately, with no voltage measurements, there's not much to do but speculate - not a very informed basis to either dispute the product with the vendor or for buying another battery or different controller... need some facts.

 

[myosis]

Yes, I will get myself a volt meter, and come back with some specs.
Thanks for the help guys!