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Discussion Starter #1
Hi everybody, I´m electro-converting a 1978 AMC Gremlin… I Use a forklift 18KW motor (48Volts) with a 2000 pathfinder manual (5sp) transmission. It moves, but its SLOW!!!... I can only use 1st & 2nd shift, to get 15mph… the rest of the shifts are ever slower.
Someone told me that I “Kill the Tranny-Differential relation” … Someone Know what kind gear ratio do I need?
I appreciate any help You can provide.
 

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Hi
What voltage are you using? - if it's low (less than 140v) then you will get the best results in top gear not bottom
 

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At 48 volts it is still a forklift. So expect forklift performance.

Yes in the old days you could run a rabbit, but there were a LOT more batteries onboard.
 

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I´m Using 48 Volts
Not enough voltage to cause enough current to make enough power.

Your motor can certainly handle 2-3x as much voltage.

However, it depends on what you're using for a controller as to whether it will be able to handle higher. If it's a forklift controller, probably not.

Looks like you've got 8 batteries, so, that's presumably 4 pairs in series. You could run a single string of 8 batteries in series, but not without knowing whether that would blow up your controller.

, & can only use 1rst & 2nd gear ... 3rd to 5fth won´t even move
Now that is peculiar. It should maybe struggle with acceleration, but, high gear should bog the motor down more and let you continue to accelerate.

5th gear should accelerate quite slowly, but, shouldn't be like, a dead stop. Maybe when you try to start in higher gear you're tripping a current limit from the torque attempt and thus your controller shuts down. But, that would not explain why you can't switch to those gears while moving really... unless you're hitting the current limit there too.

As with any inquirey, more details required.

Make/model of your controller?
 

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Looks like you've got 8 batteries, so, that's presumably 4 pairs in series. You could run a single string of 8 batteries in series, but not without knowing whether that would blow up your controller.
Not all that likely... normal practice in golf cars is to use either six 8-volt or eight 6-volt batteries (all in series for 48 volts nominal either way), and the easy re-configuration is not available in that case.
 

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Not all that likely... normal practice in golf cars is to use either six 8-volt or eight 6-volt batteries (all in series for 48 volts nominal either way), and the easy re-configuration is not available in that case.
Good point.

And looking at the batteries in his photo, looks like only 3 water ports per battery, so, almost certainly not 12v batteries.
 

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And looking at the batteries in his photo, looks like only 3 water ports per battery, so, almost certainly not 12v batteries.
Good catch. I hadn't even looked at the photo in detail. Indeed, there are eight 6-volt batteries (which appear to be the common GC2 size as used in golf cars), and they are visibly wired in series.

As already stated, this is basically a forklift truck or golf cart battery set and motor, so the performance while moving a whole car isn't all that surprising to me. What was the expectation?
 

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An 18kw 48v forklift motor will draw about 375 amps

In that car in top gear that will accelerate rapidly to about 20 kph - as in spinning tyres

But it isn't doing that so something is wrong!

I suspect one or more of those batteries us completely knackered and is basically just a resistor

Measure across the individual batteries while trying to load it
 

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Controller:pWM Curtis 1205M 5603
https://www.nocoev.com/product/1205M-5603.htm

48v, 500a controller.

48v * 500a = 24,000 watts. 750 watts per hp, so, that's a 32hp motor if you're more familiar with HP.

It takes about 12hp to travel 60mph which leaves you 20hp to accelerate and climb hills (climbing a fair hill will require about another 12hp, which leaves you only 8hp to accelerate, so, you'll be slow to accelerate when climbing). On a little car like that it's weak, but it's not awful.

The problem would be your gear ratios perhaps, as you actually have to load the motor hard enough to get it to draw 500amps if you want that kind of power.

Either way, does not explain why you're not moving (albeit slowly perhaps), so I'm with Duncan, probably a battery is crapped.

And, even then, you'll be golf kart speeds.

To go faster you need either more gear up, or, both a higher voltage controller and higher voltage batteries.

...

I'm kind of surprised that you managed to finish an EV conversion, while somehow leapfrogging a lot of the basics that would've told you that this end result was inevitable. Normally people would have hit roadblocks along the way and ended up researching or asking for help and would've got this advice much earlier. You've accomplished a lot on your own.
 

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Discussion Starter #12
I Appreciate All You Guys the advice & help to the trouble I am… I guess I should ask before
What kind of a test should I do to verify if a battery is crapped?
 

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What kind of a test should I do to verify if a battery is crapped?
Well for start, a simple voltage test.

Set your multimeter to DC volts, and then dig it into the posts on the + and - of each individual battery. No need to disconnect them.

A 6v battery should be north of 6.3v when fully charged. As high as maybe 7.2. If it's less than 6.3 charged, it's crap.

That's the quick and dirty test, but it sometimes lies to you in the positive direction (voltage looks high enough but battery is still crap).

For that you need to do a load test. You can probably buy (or borrow, or buy and return) one of these for 6v.

Or you could put your car up on stands and have someone press the gas. Just lazily moving the wheels might be enough motor load on the batteries to tell you what's up. Measure the voltage again while the motor's running steadily. See if any individual batteries are choked out in those circumstances. They'll be a bit lower with minimal load, but shouldn't be too significantly lower. If one drops from 6.3 to 5.3 under light load or somesuch, it's crap.

In fact, it's not that much to write down, I'd just write it all down.
 
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