NIMH+SLA's

[mxer]

Hi all, Just bought a spares or repairs E Bike for much cheapness ,The one with the controller and pedlec in the crank Anyway's this part is u/s electric wise but i do have a 48v controller hanging around with a throttle

Ok,The bike came with a 24v NIMH pack built into the frame (removable) but i only have at the mo a 48v controller (TBH i don't want to run 24v anyway in the future) I have two 12v 7ah SLA's and i wanted this running to see if it would work????... It does work but lacks power (Ish), head winds are a killer down to 0 almost, which i was supprissed as a 24v motor should light up with 48v through it ???....

Anyway's i'm guessing mixing chemistry is fine as i'm still alive but are there any do's and don'ts with this set up etc, for instance does it matter which way i run off the NIMH pack to the SLA's ?? ie I'm running the + feed of 24v pack to the - of the SLA and so on to finish with + from the SLA to the controller and - from the NIMH = 48v ??

Or should I run the + of the NIMH straight to the controller and the - to the SLA's to finish with a + from the NIMH and a - from the SLA's to the contoller ?, I'm starting to confuse myself now i hope someone know what i mean, and appoligise for the lack of knowledge but i'm giving it ago

I suppose basicly what i'm saying is before i wire this up permantly what's the best way to connect them up/if at all ??, Thanks in advance guy's and love this forum

 

[dogman dan]

I don't believe it makes much difference really. Just stop when the type of battery with the least capacity is drained. Maybe it's slow because you are getting so little from the tired old nimh?

 

[mxer]

Dogman, To here that is music to my ear's it has been racking my brain to find out before the permanant install, Cheers buddy I diddn't think it mattered but the lack of power made me rethink at to which + to pull through, the SLA's or thge NIMH pack.....

My SLA's are the problem i think, The volt meter on the NIMH pack with load show's a constant 26v but the SLA's are dropping rapidly to 18v so, hence my question to which pack's to pull through + or - i thought originally it was because the way i wired them up but it's clear my issue is the SLA's are just weak, but least i can get on with the install, and order some new SLA's....

Thanks again

 

[mxer]

Having another look at my controller it's not 48v it's a 36v, so even with the SLA drop to 18v and the 26v NIMH pack it's still 44v going to a 24v motor, it still should pull no??, shouldn't it ?.......Pahap's i should be pulling the power from the + of the NIMH ?, Instead of the week side of the SLA's, but then again it's still 44v :? I don't know i'll get some new SLA's and see what happends .....

I wish i had a 24v controller just to try the system as intended something tells me i would proberly get a better performance .....

 

[amberwolf]

What is the current draw at max voltage drop? 44V on a 24V motor *can* have some serious pull, but only under two conditions:
--sufficient current is provided by batteries *and* controller for the motor to develop the torque you expect
--motor is not just going into saturation and wasting most of the supplied power as heat, rather than doing useful work with it.

Could also be mechanical friction on the drivetrain or wheels causing lots of drag that is wasting the power, too. Does everything turn freely by hand?

 

[mxer]

Very helpful post amberwolf thanks, The bike is new so no issue's with drag etc, Iv'e been working today so havn't had a bit of time to do some more tests, I think i need to test the full output to the motor under load like you said and see what voltage is going there, I'm thinking the full voltage is getting there just the motor is not really using it, i only had a little test up the road so proberly not enough to get it hot (I did feel the motor and it was cold) just feel it should of been a bit more snappy with battery's fresh of the charger and it was a little limp, Even off the throttle and banging it back on while coasting diddn't really feel anything.....

Personally I just think that is it, As the motor really spins up well and fast with the wheel of the ground (very fast) just has no tourqe at all under load, the two wires to the motor are really thin 1.0mm to 1.5mm the thinest i have ever seen on a motor so pahaps not made for power/tourqe...btw i'm only 10 stone so it's not that i'm heavy taking the tourqe away........I keep testing and add some new battery's when they arrive and report back thanks guy's.....

 

[dogman dan]

Just two wires to the motor? So it's a brushed motor. That makes damaged brushed a possiblility if the motor got too hot in the past. So that could be the problem. If you can't solve it otherwise, then mabye pop er open and look at the brushes.

Perhaps it's just that weak a motor too. Some are. Or it could have been made that way. One brushed motor I smoked had magnets so weakened they wouldn't stick to a fridge. By then not running at all though. But another possibility.

 

[mxer]

Two wires is what draw me to the bike as i knew i couldn't go wrong with wiring it up I'm still at the very basic's and motors with several wires coming out of them scare me as all my controllers have two wires for the motor (I must do some more reading)......

The motor is new too and has only had the 48v through it for 5 min's max, so can't be damaged yet as i never experienced any drop in power from the first instance.... I will have a look tommorrow for some more testing...... i'm determind to get something outta this bike. I must be doing somthing wrong :?

 

[amberwolf]

Not necessarily--as I said, the motor could be going into saturation (magnetically) and simply wasting most of the input power as heat instead of making mechanical force with it.

It would definitely help to know how much current (amps) is flowing out of your battery when the voltage drops during maximum load on the motor.

Remember also that your controller probably limits current to prevent damage to itself, so if that's a really low limit it won't feel like you get much torque from the motor, usually.

 

[mxer]

Just found out my controler is only putting out 250w, Would this make a difference ? and be causing the lack of power ?if so what would be the best wattage to go for 350,500,750? My motor is a 24v 250w brushed, i'm trying to run 48v through it with a 24v NIMH (9ah) pack and two 12v SLA's (7ah) wired to 48v...Cheers guy's

 

[mxer]

Just ordered a 48v 750w controller, That should melt it :lol: :lol: :lol: