Adjustable 12v contact (surface) aquastat for mobile application

vtfarmer

Hi Everyone!

A couple of years ago I retrofitted a Detroit Diesel 3-53 engine into this 1963 Trojan front end loader (which has a lot of sentimental value to me) in the place of an old International Harvester gasoline straight six that was very tired. Because the Detroit is about 2/3 of the length of the original gas straight 6 and the Detroit is meant to have its fan mounted up high on the block, like a semi engine, I couldn't make the mechanically driven fan work.

As such, I procured a 12 volt electric fan (from an old Volvo) and adapted that to the radiator. I works great, but I need an aquastat to cycle it. I do not have an available tapping on the engine to put an immersion thermostat and I want to be able to adjust it anyway.

The fan draws about 25 amps at 13 volts, DC.

All of the non-mercury Honeywell suspects aren't rated for switching DC loads and the products designed for automotive applications all involve a relay (a mercury switch woul be great except the machine is not always level). Am I stuck using two components? Or is there an aquastat out there that's rated to switch 30A DC?

EBEBRATT-Ed

Maybe use an aquastat with a relay and let the relay do the switching

vtfarmer

https://forum.heatinghelp.com/discussion/comment/1819045#Comment_1819045

That's the obvious solution, but before I go that route I'd like to know if the Brain Trust is aware of a device which will do what I want all in one. Probably not, but you don't know if you don't ask :D

vtfarmer

To be clear, I am 98% likely to buy this kit or something like it:

https://www.ebay.com/itm/153780937172

but I wanted to post here first in the hope of someone like @Jamie Hall or @EdTheHeaterMan coming along and pointing out that some long gone company made heater controls intended to be used with the 32 VDC power that the old rural homestead Delco light plants put out, or that the HVAC controls used on Bombardier subway cars from the '70s switched DC loads and might be suitable…you never know.

Jamie Hall

The problem isn't the 32 volts DC. It's the 30 amps vs. the Aquastat. Opening a DC circuit is going to draw a decent sort of arc (switching DC is very different from AC — in AC, unless a plasma forms (and it won't at that voltage), the arc and the current and the heat stop at the end of the first cycle. DC it will just keep going until the contact opening is great enough), and if it's a 30 amp circuit there's going to be a lot of heat — and the contacts in an Aquastat just aren't going to last.

Larry Weingarten

Hi, I'm wondering if some sort of slow start device could be put inline to prevent that big inrush of current? 🤔

Yours, Larry

Kaos

This is standard aftermarket car part ie:

https://www.jegs.com/i/JEGS/555/52125/10002/-1

Many others out there. If you need more currant use the switch to drive a relay rated for the fan current. This is how it is done on most older cars.

hot_rod

I was think more along the line of these snap disc bimetal controls.

This company has a lot of temperature control options.

https://www.sensience.com/bimetal-disc-thermostats/

Screenshot 2024-11-09 at 7.30.28 PM.png

vtfarmer

https://forum.heatinghelp.com/discussion/comment/1819074#Comment_1819074

Thanks Larry. This is a mechanically commutated DC motor, so the inrush is about the same as the running current but I like where you're thinking.

https://forum.heatinghelp.com/discussion/comment/1819077#Comment_1819077

I've used those types of setups before but have not been happy with them. I've had the cheaper relays weld together then never shut off and I've had moisture get into the crimp connectors and relay base.

https://forum.heatinghelp.com/discussion/comment/1819078#Comment_1819078

BINGO! I was not aware that higher amperage adjustable make on rise snap disc thermostats were available. This is exactly what I came here looking to learn, thank you so much! I'll update the thread with how it works out.