I am looking for a relay that doesn't use power all the time

[mikenr]

Hi there, I have recently wired my solar system that half my array is diverted to an immersion heater when the battery is at 100% (possible with my MPPT charge controller that will control a relay for me)

I have wired it using car relays, so when the relay is energized the power is routed to the immersion heater, it works fine but I didn't realize that the two relays (one to switch the positive and the other negative) use 4amps at 12v all the time they are energized!

Can anyone tell me if there is a suitable type of relay that will only use power to move the contact and then no longer use power until it switches back again? I am switching 180w from the panels (30V at 6amps)

Many thanks in advance for any help!

All the best

Mike ;o)

[Mike90250]

There are Latching Relays, and Solid State relays. You may have to hunt a bit. to find one with the specs you need.

[mikenr]

There are Latching Relays, and Solid State relays. You may have to hunt a bit. to find one with the specs you need.

Many thanks for that, I'll have a look around the internet and see what I can find!

Thanks again

Mike

[inetdog]

Note also that there are two basic kinds of latching relays: Mechanically latching and electrically latching.
In the first case, the relay uses no power at all once it is in the selected state, but you have to apply a controlled pulse of current on the correct control line to move it ot the other state. Sometimes it is harder to make the logic to apply the pulse than it is to just run the relay current.
In your case, set the relay coil up to have power applied only when you want the diversion turned on and you have power to spare.
Electrically latching relays will still use coil power in one of the two states, but you do not have to continue to apply the control signal to keep the relay in that state.
This gives you the logic problems of the mechanically latching relay without the benefits. This design it typically used for a motor or device that needs momentary START and STOP buttons.

[bcroe]

Hi there, I have recently wired my solar system that half my array
is diverted to an immersion heater when the battery is at 100%
I have wired it using car relays, so when the relay is energized the power is routed to the
immersion heater, it works fine but I didn't realize that the two relays (one to switch the positive and the other negative) use 4amps at 12v all the time they are energized!

Can anyone tell me if there is a suitable type of relay that will only use power to move the contact and then no longer use power until it switches back again? I am switching 180w from the panels (30V at 6amps) Mike

For relatively low power, couldn't you just tie perhaps the negative permanently, and switch
the positive? With a common rail, a few parallel MOSFETs could close the circuit at almost
no power loss. A CMOS flip flop could hold the last momentary input. A mechanical latching
relay is elegant, but they are uncommon. Could make one from some mechanical switches
and a small DC motor drive. How about, tilt a mercury switch? Bruce Roe

[Robert1234]

Not sure I should provide a link, so I'll just say it with words....

AMETEK makes permanent magnet latching contactors. Power is needed to both latch & unlatch the circuit, but no power is consumed between functions. Just realize that when the contactor is closed, it is closed. You need to be able to apply power to the contactor to open the circuit again. Look at the JAY46 as a basic example.

[inetdog]

Not sure I should provide a link, so I'll just say it with words....

Links to specific commercial products as long as they are not on sites which compete directly with our sponsors are usually acceptable, but use some common sense in making the decision.
Links from new posters will be scrutinized more closely.

[FunGas]

I use something like this to switch power, they are very fast, silent and work from 3V to 24V.

[Robert1234]

Inet - Gotcha.

FG - Good maybe for this application, but I'd smoke that unit in my use so fast it would be scary.

[Sunny Solar]

Fungas a SS relay like you have shown is an excellent choice but even better if you can get one rated at 100 a . They are physically about same size. Their current draw is in the milliamps .
Ihave used hundreds of them . they are gret for use in vehicles for headlights /spotlights Heavy duty accessories.

If used to switch above about 30a they will need mounting on a aluminium heatsink .