Multiplus Relays - power from pos terminal stud?

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blindbadger asked Mar 28, '24

Multiplus Relays - power from pos terminal stud?

I'm looking to wire up auxiliary PC fans for my multiplus to help provide it fresh air and was thinking about using the K1 relay connections for them

For the relays, I understand that a common way to wire them is:
- COMM from battery positive (with an inline fuse)
- NO to load (negative on load to battery negative)

Is there a reason not to get the positive connection from the battery stud on the MP? Or is it better to run the longer wire to go back to my distributor (my multiplus is mounted about 10ft away from the battery and loads bus bars).

Multiplus-II Relay

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Answer 1 · 2024-03-28T19:21:02Z

delf67 answered · Mar 28 at 07:21 PM

The relay wiring you describe refers to "volt free" contacts. I'm not sure that's how the K1 terminals are used. They are labelled + & - (not Com/ NO) and are described in the manual as:

1. 12V 100mA

2. Programmable contact K1 open collector 70V 100mA (whatever that means).

The alarm relay is regular volt-free contacts (Com/ NO/ NC), so you might be better off using that.

As to your actual question; I can't see any reason you shouldn't power the fans from the battery studs on the MP.

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blindbadger commented · Mar 29 at 02:40 PM

I'm running a Multiplus 1 24/3000-70, so maybe it's different on the MP2? My K1 is definitely a NC/NO/COM setup of terminals.

The "Primary Relay"/Alarm Relay is up near the top and much bigger, so I could use that too. K1 is just a bit easier to get to and route wires to.

I have Aux ports that's +/- (over left of the negative battery cable) but my understanding is that is more for switches. For that, would it still be 12v if the inverter is configured for a 24v battery?

Also, please forgive the small cables on the inverter...it's connected to a temporary battery and the limits are set low to accommodate the smaller cables until I finish the battery bay with proper 2/0 (hopefully tomorrow).

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delf67 blindbadger commented · Mar 29 at 07:33 PM

Yes, sorry, I assumed MP2 even though you did say MP.

On the MP2 the Aux1 & Aux2 are described as configurable analogue/digital input/output ports. But doesn't say any more than that - helpful.

As long as your K1 relay is rated for the current (which I imagine for fans is going to be fairly small), that seems like the simplest option. How are you going to switch it, with a relay assistant?

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blindbadger delf67 commented · Mar 30 at 03:05 AM

Yeah with an assistant. I had hoped I could use the temp sensor but it didn’t look to be exposed for use so I may either tie it to the existing fans as “helper fans” or just wire a switch to sort the aux inputs to act as a switch to turn the fans on manually.

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Answer 2 · 2024-03-29T19:26:25Z

kevgermany answered · Mar 29 at 07:26 PM

The stud will be at battery voltage. Not good for 12V pc fans.

Relay specs are in the notes of the technical specification section of your manual, I think it's 240V, 4A, but can't be sure.

There's a good fan in the multiplus. Do you need another? Ensuring good air flow to and from it should be enough.

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delf67 commented · Mar 29 at 07:40 PM

He could run 2x 12V fans in series.

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kevgermany ♦♦ delf67 commented · Mar 29 at 07:50 PM

Or a buck converter

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blindbadger delf67 commented · Mar 30 at 03:02 AM

Yeah, series was my plan for the fans. The multiplus is mounted on its back due to space constraints so I wanted the fans to help keep fresh air flowing through it to help.

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kevgermany ♦♦ blindbadger commented · Mar 30 at 09:25 AM

I think you'll find it blows out at the top, so good ventilation at the bottom and extraction at the other end.

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