View Full Version : ThermoKing SB III SR Project: conversion to Electric motor

23-05-2017, 11:28 PM
This subject may already exist elsewhere, but i didn't see it.

We have a Small Fruit Farm.
I recently purchased n older trailer 94' model with a side door and roll up door.
My goal was to use it as an on farm walk in freezer, freezing fresh fruit seconds for use in value added products at a later date...basically using the freezer to buy me some time until i can get to them.
The trailer seems pretty tight. Engine starts right up, it gets cold etc.
My question is in regards to an electrical conversion.
I intend to pull the diesel engine out and replace with a 15-20hp 240vac 1p motor.
54000 btu max is just over 20hp... my thermal load will be small so i don't see me pushing this threshold.
Has anyone here had any experience with this type of conversion?
What electric motor Frame do i need to be looking for? is there something like a TC frame that would readily bolt up? Can/Should i do direct drive with a lovejoy type connection or should i look at doing a belt/chain drive system?

Any advise is welcome and apreciated???

Model SB III SR 32000 btu at 0 degree
wabash -10 degree frozen transit

charlie patt
24-05-2017, 07:49 PM
Never worth the hassle even on a 30 the never ending pulling up belts for fan would be never ending rip it out and fit commercial kit and if your removing the engine how you powering low voltage solenoids you have no alternator the list is endless

24-05-2017, 09:28 PM
I agree,it's the single phase that would be the issue could you get single phase equipment with enough power to cool a box that size down although you could fit a couple of systems?

25-05-2017, 02:38 AM
I contacted a thermoking dealer. The motor from them is $950.00, 400$ for the bracket, another couple of hundred for the Controls....

I can fabb the bracket, and Control power is as simple as a power supply. 120/12v.... Motor is set up direct drive.

I'll try to source locally for most of the parts...

25-05-2017, 02:39 AM
I'll do a three phase motor with an inverter... The Quote for a 15hp 1phase was 3500$

25-05-2017, 03:39 AM
5000 dollars plus,you could fit commercial kit for less plus it would use less power no brained then when you build a proper store you could reuse the equipment?,or is it me that's missing something.

25-05-2017, 12:51 PM
I'm with Cad, a commercial unit would be a much better route. More efficient and more reliable. I've seen a few reefers used as long term storage and it never seems to work right.
Another suggestion would be a sea can. You'd need some phase conversion to run it but the insulation is much better. The R-value of a 20+ year old box with a roll up door is about the equivalent of a cardboard box.

28-05-2017, 02:21 PM
I appreciate the alternate ideas. But I own the trailer. It runs very well, and holds 0 on the cycle on/off mode.

I am an industrial electrician. Wiring it is not an issue.
I contacted my local thermoking dealer, who put me in touch with one in Wisconsin I believe.
After speaking with them, it's a fairly common issue. They offer a kit, with brackets etc.... But I'll fab and install myself.
He talked me through it. The 3ph 15hp motor is just under a grand. I'm looking for a cheaper one. But I'll run it off a 3p 240/208v 50% derated 1phase inverter.
I've actually done this for a customer years ago for a peice of equipment that was critical while the 3phase utility was replaced. Not sure why I hadn't thought of it previously.

Low voltage will be provided via a 120-12v power supply. They're readily available.

I'll need to install a relay contactor to control the drive input. But it'll be easy enough.

All in all I should get it done for less than a couple of grand.

The Electric motor offer reliability in the form of a constant power supply. That doesn't need the fuel refilled twice a week, at 200.00 + a week.
And the BTUs per hour produced via Electric motor are substantially cheaper than on the diesel engine.

I have been giving thought to enhanced insulation. I will build the cross wall from 4" closed cell IMP, it's got me thinking that I could decrease my thermal losses via adding a layer of the 4" IMP to the floor as well. I happen to posses enough to do this. It's the tounge and groove commercial type. I'd have to deal the edges, and there would be an added step up but it would certainly reduce the losses I would think?

I realize this is in Orthodox to some, but like I said I already own it. It's just come off the road. Is in good shape. And I only need to run it 4-5 months a year.
My polar king walk in cooler does fine with this treatment.