Will a 24V 16A relay work?

[Lucien Nunes]

Yeah but... a relay with a N/C contact good for 100A+ is not a cheap off-the-shelf item.

 

[telectrix]

3 pole contactor??? use 2 poles, split the load??? problem could be (energised in normal circumstances.

 

[Das_DIY]

Thanks All for your responses and suggestions!!

 

[Lucien Nunes]

Tel has a point, you can parallel poles to gain extra current rating, although current sharing isn't guaranteed and if one contact goes high resistance it puts more load onto the others. This sort of think would do the job but it's not cheap:

40A 230V 4 Pole 4 NC Contactor

Ideal for heating, motor control and lighting loads

www.cef.co.uk

Hence my preference for a single-pole, high current N/O DC relay energised off the battery when a small N/C mains relay releases. Although that has its own drawback; taking the relay current from the battery could measurably reduce the standby time depending on the standby load of the inverter.

But I think the relay is a red herring. I would find any possible way to avoid using it.

 

[pc1966]

Tel has a point, you can parallel poles to gain extra current rating, although current sharing isn't guaranteed and if one contact goes high resistance it puts more load onto the others.

One trick is to have all of the cable tripled up, etc, as well from source to load so in effect they form "load sharing" resistors.

But it only works well if the cable R values are a few times worst-case contact resistance, so longer the cable (within reason) the better.

 

[Rockingit]

Unless I'm missing something here, isn't it just easier to run the battery charger 24/7 and use a relay on the 230 line side of the inverter??

 

[Lucien Nunes]

The 230V transfer switch is a whole different kettle of bananas. The OP hasn't mentioned it yet and I've avoided the issue. If it were me, I would leave the battery charger permanently connected and hack the inverter to give a remote standby, controlled by an opto-isolator from the mains. But can't really advise that to a DIY poster.

Actually, @DasDIY, how were you going to switch over the 230V AC side of things? If you are doing that manually, can't you switch the inverter on manually and save the complications?

One trick is to have all of the cable tripled up, etc, as well from source to load so in effect they form "load sharing" resistors.
But it only works well if the cable R values are a few times worst-case contact resistance, so longer the cable (within reason) the better

I do this with multipole connectors for my battery-powered equipment. One pole and core is adequate for the load, but by using two separate identical cores in the cable I can get reliable current sharing so that no contact ever carries more than half its rating, reducing heating and enhancing lifespan and reliability.

 

[Das_DIY]

What if i avoid the relay altogether and use a rocker switch instead? on/off/on to charge battery or feed inverter.

 

[i=p/u]

1kw inverter trip out on fridge alone ???

 

[i=p/u]

Contactor is way to go but need to limit load in house I.e lights and 1 socket..