Powering 12v Kids Gator XUV from 56v Batteries

[fuzzoli]

Posting for a friend -- really.

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So here is the deal. I have a 12v gator for my kids. I have a bunch of 56v ego batteries. I want to step down the voltage and drive the 2 12v motors via the ego battery

So 56v -> pwm/buck converter/something -> 12v motor

The 12v really can be anywhere from 11v to 18v and its fine. They are 170 watt motors at 12v so they are 14 amps at peak running but after measuring they pull around 9 amps each when already moving.

The struggle. When the gator is not moving at all, the start current is 3X the running max. So I am seeing around 30amps per motor for a few seconds. So I need to be able to step down the 56v dc to 12vdc and support 20amps consistently and 60 amp spikes when starting from a static position.

The step down bucks on amazon can support 60 amps but they have input voltages of around 48v, not 60v. The ones that support 60v(typically the 72v range) don't support 60 amps. Struggling to find a solution

I did get a 60v 50amp pwm controller which worked great for like 20 minutes but it burned out so I figured I would stay away from pwm or I would need to run two of them(one for each motor)

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I took a crack at some ideas but nothing was economical.  DigiKey had some DC-DC converters within the desired range, but are crazy expensive.  There's a ton of power being thrown around (and out) here, and I'm out of ideas.  I will have to check, but I don't think hacking the batteries is a viable solution.  There are a few YouTube videos out there on similar conversions, but 1) nothing with such a high battery voltage, and 2) I give much more credibility to this forum than YouTube.

Any thoughts on a possible solution? 

[james_s]

You could build your own buck converter from scratch, it's not trivial but as far as SMPS stuff goes it's about the easiest topology there is to get right. Seems like Linear Technology had some ICs with relatively high input voltage ranges.

[Circlotron]

I'd favour some kind of isolated converter rather than a non-isolated buck. If it fails it will present the full 56V to the motors and your kids will likely go into orbit. Isolated converter will fail safe.

[srb1954]

Posting for a friend -- really.

==========

So here is the deal. I have a 12v gator for my kids. I have a bunch of 56v ego batteries. I want to step down the voltage and drive the 2 12v motors via the ego battery

So 56v -> pwm/buck converter/something -> 12v motor

The 12v really can be anywhere from 11v to 18v and its fine. They are 170 watt motors at 12v so they are 14 amps at peak running but after measuring they pull around 9 amps each when already moving.

The struggle. When the gator is not moving at all, the start current is 3X the running max. So I am seeing around 30amps per motor for a few seconds. So I need to be able to step down the 56v dc to 12vdc and support 20amps consistently and 60 amp spikes when starting from a static position.

The step down bucks on amazon can support 60 amps but they have input voltages of around 48v, not 60v. The ones that support 60v(typically the 72v range) don't support 60 amps. Struggling to find a solution

I did get a 60v 50amp pwm controller which worked great for like 20 minutes but it burned out so I figured I would stay away from pwm or I would need to run two of them(one for each motor)

===========
I took a crack at some ideas but nothing was economical.  DigiKey had some DC-DC converters within the desired range, but are crazy expensive.  There's a ton of power being thrown around (and out) here, and I'm out of ideas.  I will have to check, but I don't think hacking the batteries is a viable solution.  There are a few YouTube videos out there on similar conversions, but 1) nothing with such a high battery voltage, and 2) I give much more credibility to this forum than YouTube.

Any thoughts on a possible solution?

Use two converters, one for each motor. A 56V to 12V 30A converter might be more readily available and cheaper plus the wiring will be easier with lighter gauge cables.
 or
If the two motors are always running at the same power level wire them in series so you can use a 56V to 24V 30A converter.

You will probably need some substantial reverse polarised diodes across each motor so that any back EMF doesn't feed back into the converter and damage it. Some large electrolytics across the converter output to absorb surges would be useful and they will also help with the starting surge (provided you switch the motor power after the converter).

[Circlotron]

If the two motors are always running at the same power level wire them in series so you can use a 56V to 24V 30A converter.

If the two motors drive the rear wheels completely separately, or the front and rear axles separately then putting the motors in series will provide a handy differential action.