Voltage controlled contactor

[ajh]

I'm probably using the wrong terminology so not having much success googling; a long time ago I snagged and serviced woodchip stoking boilers, the control was largely by Omron programmable temperature controllers.

A set temperature could be stored in the device and when reached a supply to a fan or auger would switch off, a second temperature could be programmed to switch the supply back on once the temperature had fallen a few degrees, to allow a bit of hysteresis between off then on again.

I now am looking for a device that does much the same but is controlled between two DC voltages in the range of about 54V to 52V in 0.1V increments

Suggestions welcomed.

[Fredxx]

My immediate thought was a voltage sensitive relay.

Could you use something like:

With some external relay(s)?

[The Natural Philosopher]

Arduino with ADC and a mains relay? And a 3D printed case! All the rage.

[Fredxx]

I was wondering about a processor oriented solution, but it seems quite a faff for a simple function.

I think a relay capable of being driven by an Arduino might be an issue? Actually an SSR would do the trick.

[Theo]

I can't immediately think of an off the shelf widget for this.

The voltage levels are a bit awkward but I wonder if it would be possible to use a voltage regulator to make say 48V and 56V levels. Then string an opamp off those two as supply rails. Your input would look like 4V to 6V as the opamp is concerned.

You'd probably need a lot of clamping to stop voltages going out of range, but it might be more robust than using a resistive divider to get within the range of an ADC (eg a divide by 20, where your 0.1v step would become 5mV) without being susceptible to noise.

Depends how 'industrial' it needs to be, and how it behaves in the presence of noise and fault conditions. Getting 54V in the wrong place for most ICs would cause a bad day.

Theo

[ajh]

Yes this looks a good bet and cheap to try, it would have to drive a

240V contactor somehow.

[Theo]

Looks like it's switch mains at 10A directly, or you could just feed the switched output into an external contactor. It appears the output is isolated so you could use a main AC contactor, although I might be tempted to use a DC contactor powered from the same power source as the unit is powered from, to avoid putting mains into the unit.

Theo

[Fredxx]

There are Arduinos, and I think there are off-the shelf enclosures. A SSR (Solid State Relay) can run with standard logic levels so can driven directly from an Arduino output pin.

The input would need to be reduced, say through a potential divider. There must be some "HAT"s with ADCs. With a bit of research there is probably a project that can be modified.

However I am conscious this is now a project and not a quick fix for the OP.

I thought we were talking about switching mains?

[ajh]

Yes I shall use it as is to test the principle and if it does what I expect I shall then use it to drive a two pole contactor.