under performing!!??

[steelefist]

What are the main reasons why a 750 watt 36V motor coupled with a 48V 14Ah NiMh battery pack system would grossly under-perform in both acceleration and top speed? The pack has blown a 35A fuse when shorted, but maximum throttle has very poor results.

 

[Ypedal]

Need to quantify " underperform " .. compared to what ?

Motor model ( hub ? or chain driven ? ) and brand ? controller used ? bike wheel diameter ?

Got a CA meter to report voltage sag under load ? etc..

 

[steelefist]

I mean by the acceleration feeling weaker than a 250 watt scooter. The top speed is around 12mph. With this set-up the top speed should be around 26-28 mph. the motor is failing to reach maximum rpm when loaded. Could weak connection between the cells in the battery pack cause this?

 

[dogman dan]

Id be looking at the controller, and also any bad connection, including one inside the motor could do it. does it perform ok with a different battery?

 

[monster]

swap components and use process of elimination to find out whats wrong or use fechter's fault finding techniques found on the sticky threads. if you still suspect the battery you could test it using a pcs10 data logger to log volts and amps during discharge over a light bulb.

 

[Lessss]

sounds like a mismatch in controller and motor

 

[needWheels]

"48V 14Ah NiMh"

This sounds like it's built out of F cells, any chance it's Tenergy?

Is it a new pack? Maybe they can't do more than 1C and it's choking.

 

[Ypedal]

It's a simple test..

Got a volt meter ?

Get a friend to help.. plug in the battery to the motor.. lift the wheel off the ground. spin it up full throttle. make note of speed and what voltage you get on the battery..

Apply the brakes to load up the motor and check the battery voltage while you do this..

report back.

What model motor/controller ?

 

[fechter]

I'd guess serious voltage sag on the batteries under load. Get out that voltmeter.

 

[dirty_d]

ok what kind of motor and specs, ie no-load rpm and stuff? hub or chain drive, if its chain drive did you make it yourself? what is the gear ratio?

 

[steelefist]

It's a 750 Watt My1020 36V motor but over volted to 48V the controller is a 48V LB-37 from tnc scooters. Yeh there are 40 of them F size 14Ah cells from all-battery.com. They say max output 65A on the site. It's chain driven and there isn't any significant resistance from the brakes or over-tension in the chain. At the moment I'm rebuilding the battery pack to rule out faulty connections.

As soon as I got the batteries they were each reading 1.23V. I didn't charge them initially assuming they are fully charged. Being NiMh it's important not to over-charge the batts, even tho the charger does have auto-cut off. was just being over careful perhaps. Could this be the reason?

 

[docnjoj]

Yes! Full charge should be in the 1.4 range per cell!
otherDoc

 

[dirty_d]

but what is the gear ratio and wheel size? if you have too low a gear ratio you will have a low top speed, too high and you will have very slow acceleration and low top speed too.

 

[needWheels]

Don't NiMh have to be "broken in" with a few discharges/recharges before they exhibit full capacity?
Maybe this is what they are running into?

 

[Doctorbass]

also some controller have a ramp capacitor that smooth the throttle increase.. maybe to decrease the value... some DC controller take like 1,5sec to activate full power when throttle grip wide open..

Doc

 

[Lessss]

open your controller and make sure there isn't a river of solder running off into the corner.

 

[steelefist]

The gear ratio is a 13 tooth sprocket on the motor to a 54 tooth on the wheel. The same ratio was used b4 i modified the scooter. I'll give all the packs a full charge and see if there is any difference. Was really disappointing riding along will max throttle and barely doing 12mph.

 

[steelefist]

Ye was the charge of the batteries that was the problem. Just tested it down the road there and got sum serious torque from it upto bout 20-22mph b4 i chickened out! Tyres need inflating.

Does any1 know wot voltage each NiMh cell shud be after charging?? Doc mentioned around 1.4V. What is the safe maximum? its just I have 2 universal smart chargers chargin up 2 packs at a time but I haven't had the green trickle charge light cum on yet! I stopped the charging to read the voltage at 14.4V for the 10 cell pack. Just concerned that if the charger doesn't stop as it's meant to would it destroy the batteries much above this 1.44V per cell!?