Lithium battery upgrade

[Gray Fox]

Has anyone tried the battery kit from big battery.
It has 2 48v at 40ah connected in parallel to give 48v at 80ah. The spec says that they will provide a Max continuous 126 ah. This is what I was looking at buying to upgrade my 1999 36v txt to 48v using heavy duty solenoid and navitas 440 controller.All suggestions welcome.

[ringkingpin]

I don't get it, if they're 40 amp hour batteries each, how do they get to 126ah?

[Volt_Ampere]

Something is wrong there. Maybe he meant 126 amps. 80AH is ok but not excessive. Depends on how you plan to use the cart.

[DaveTM]

If it is wrong....and I can't see how it would be right.....a "max continuous 126 amp draw" would never be enough for my hunting cart on the hills where I live.

[ringkingpin]

Amp hours is a measure of capacity. Just because you have 80 amp hours doesn't mean that the battery can't dish out significantly more amps.

[ringkingpin]

Originally Posted by DaveTM

If it is wrong....and I can't see how it would be right.....a "max continuous 126 amp draw" would never be enough for my hunting cart on the hills where I live.

How many amps is your speed controller? I have a 650 amp speed controller and opted for 6 of the 48v lithium batteries at 30amp hours each to create a bank of 180 amp hours. I did this so that there would be plenty of head room and the battery management would never go into safety mode.

[DaveTM]

Originally Posted by ringkingpin

How many amps is your speed controller? I have a 650 amp speed controller and opted for 6 of the 48v lithium batteries at 30amp hours each to create a bank of 180 amp hours. I did this so that there would be plenty of head room and the battery management would never go into safety mode.

My Alltrax Controller is a 650amp model. When I installed my Lithium pack I hooked up a laptop to the Alltrax and took a ride that is fairly typical of the terrain that I hunt.

My maximum amp draw was 345 amps when I ascended a pretty steep hill.

In order to lengthen the "milage" of the pack, I adjusted the Controller to limit the maximum draw to 40% of the 650 amps....or 260 amps. I then took the cart on the exact same drive and when I went up the steep hill the cart did so with no noticeable decrease in performance.

Before adjusting the controller I placed a call to the Alltrax engineer's to make sure my understanding of the "limit %" was correct.

I've been hunting ever since, going up (and down...BRAKES!!) steep inclines with no problems.

I hope this helps.

[ringkingpin]

Thanks Dave. So I wonder if they're actually even capable of getting up to 650amps? My solenoid is rated at 400 amps so you'd think it'd melt that if that's the case, right?

[DaveTM]

Originally Posted by ringkingpin

Thanks Dave. So I wonder if they're actually even capable of getting up to 650amps? My solenoid is rated at 400 amps so you'd think it'd melt that if that's the case, right?

Well, as I understand it the controller is rated for the 650 amps, but the motor capacity may never be "enough" to demand that much of a amp draw.

It's also my understanding that a controller can go above the rating for a short "burst" of requested amps....if the motor is demanding it.

I think the same applies to a solenoid....but I could be wrong on that one.

[ringkingpin]

Originally Posted by DaveTM

Well, as I understand it the controller is rated for the 650 amps, but the motor capacity may never be "enough" to demand that much of a amp draw.

It's also my understanding that a controller can go above the rating for a short "burst" of requested amps....if the motor is demanding it.

I think the same applies to a solenoid....but I could be wrong on that one.

OK, I'm starting to make sense of it all. My big question to myself is will a new 600 amp speed controller get me to the same speeds as the 650 D&D I have and the short answer is yes. Since lead acid batteries will give all the power they have when demanded of them, they'll just give dishing out power until they fail. The Lithiums we have, have a nice BMS that cuts the power when it gets into the danger zone. When voltage drops, such as with lead acid batteries, the amps go WAY up which results in a lot more heat. Since the voltage on these bad boys don't drop, we see very little heat generated on the wires or the motor. This means that the motor with these batteries will be much happier and last longer. 1 mechanical HP is 745 watts. I have a GE 5.5 hp motor that spins at 5750rpm max. If you get 745 x's 6 = 4470 / 48v = 93amps. So that is the max constant draw needed to get this motor to full tilt. I suppose the amps raise a bit when I go up hills but I think very little since the voltage stays pegged so I can't imagine my amps getting anywhere close at all to 600 amps on a normal mappings. My mapping currently starts off very mellow and it's not until you floor the cart and it's moving around 15mph that it takes off like a rocket. I think the reason these huge controller are made are to accomodate the needed headroom due to voltage drop on flooded batteries.