MPPT RS External Temperature Sensor Alternative Use?

Does anyone know if the wired temperature sensor which comes with the MPPT RS 450/100 can be used for purposes other than battery temperature (temperature compensation is disabled on the MPPT via Victron Connect since a Freedom Won with its own CAN bus BMS is used) to control one of the MPPT RS’ relays and switch on a remote fan to cool other components when certain temperature levels/conditions are reached? Also, can I access this temperature measurement on VRM? I am only able to find it on the MPPT via Victron Connect and nowhere else.

It also seems the relay function when configured via Victron Connect only has preset options relating to the MPPT’s internal temperature and cannot be configured to an external temperature sensor with specific temperature level conditions such as what is possible on the Cerbo GX. I have a Cerbo S GX and as such don’t have ports for a wired temperature sense available and would prefer not to buy a bluetooth Ruuvi temp sensor.

It seems in VE-Configure the Multiplus also only allows preset relay functions based on its internal temperature not the external wired temp sensor nor specific temperature level conditions such as on the Cerbo.

I doubt it is possible but thought I’d ask incase one of you Wizards have a workaround which won’t lead to additional costs :smiling_face:

Do you have a GX device?

Looking at Temperature Sensors [Victron Energy] (the page doesn’t load last column properly which I’m assuming is what you have, but if you export it to PDF it shows it) the sensor that comes with the MPPT RS looks exactly like the sensor that comes with a Multi / GX. If that’s the case you should be able to plug that sensor into your GX and use it like that.

  • From the documentation it shows that if it’s plugged into the MPPT RS it won’t show on VRM.

I have (for example) two temperature sensor plugged into my GX. One is dangling under my MPPTs at around the same height as what the Multi’s vent sits and another is right above the Multi and I’ve called them Inverter In (although it’s affected slightly by the MPPT’s heat it’s close enough that I use it to gauge the temp going into the Multi) and Inverter Out and they are purely used as temperature measurements to display in VRM and I’m not doing anything more with them.

In my case I plugged them into the GX, changed them to be Generic and renamed them and they show up nicely in VRM.



I am assuming the smarter guys will be around soon, but I am going to guess that you may be able to take those measurements and use that to open / close a relay which will allow the fan to be powered on / off. Most likely with Node-RED.


Thanks for your feedback, interesting to hear what you did with temperature measurements on the Multi’s in and outflow vents.

Sadly I have this problem as mentioned,

The only way for me to use the hardwired temp sensors (as far as I know) is via the RS MPPT’s t sense input or the Multi’s and it doesn’t seem like there is way to get this into VRM nor activate relays based on temperature measurements such as what is possible on the Cerbo. On my Cerbo S GX it seems it is only possible via a bluetooth temp sensor which I don’t have.

Oh and I have 2 sensors the one that came with the Multi i.e.the ASS000001000 for GX and Multi devices. And the ASS000020000 (last column you mentioned) which came with the MPPT RS. Glad you mentioned this because I only noticed now they are different, thought it would be the same sensor.

Forgot to mention I don’t have a Multiplus GX just a Multi II and a Cerbo S GX

Oh wow. I’m starting to become like my colleagues and only half-reading before replying. Completely missed that part. Sorry about that!

Yeah, that seems to be the case based on the page as it also mentions it’s not available via VRM. As the GX is the heart of the system and the one that talks to VRM it sort of makes sense.

Just out of interests’ sake: Different how? From the pictures they look to be exactly the same, so I’m just wondering if that can be used on a (non-S) Cerbo.

Apart from the blue sticker and bootlace ferrules on the MPPT RS temperature sensor i.e. ASS000020000 it seems the thermistor is also longer as per attached picture. Apart from that sadly I can’t offer more information and not really keen on cutting open the heatshrink to see exactly what is under the hood :blush:

For all we know they might be identical and only the heatshrink differs, not sure

Thanks for that. Seems to be the same, so pretty sure it’ll work in a non-S GX, but yeah, that still doesn’t help you I’m afraid.

Looks like I’ll have to get a Ruuvi bluetooth sensor unfortunately. By the way what fans are you using, DC or AC and Voltage? Seems 55.8Vdc fans, even 48Vdc or 60Vdc with a wide enough voltage tolerance, are quite scarce so I won’t be able to tap off the DC bus with a fuse and not planning on getting a DC-DC converter.

So currently considering using an AC fan and trying to keep the wiring isolated from the DC bus as much as possible.

Seems like the Cerbo relays are fine with 125Vac and 6A but I have 230Vac so will have to switch the fan via another relay I guess?

Here I have a Un = 60Vdc (on coil) relay in mind with voltage range 0.8Un-1.1Un to account for DC bus fluctuations depending on battery SOC and loads. This relay coil will then be switched via the Cerbo relay from the DC bus and the load side of the relay will carry 230Vac to an AC fan.

Seems like quite a schlep just to install a fan though, perhaps I am missing something?

Cerbo S GX Relay Specs - Copy

I’m not running any fan. I purely use the temperature sensors as temperature sensors and have them displayed in VRM. Just thought I’d try and help, but misread the Cerbo-S part.

This is where the smarter guys will have to jump in I’m afraid.

Disclaimer: This is way outside my comfort zone and I haven’t done anything like this, so don’t take this as fact.

What I’m thinking you can do, depending on what / how you want to wire it might be to get something like a Sonoff Mini and wire the relay to switch that on/off while having it wired to AC and the fan.

What I will also throw out there is that you can also look at a Node-RED flow that can switch on/off a plug/switch for example.

I guess these will be more expensive / schleppy than switching a cheaper relay, but that’s what I know some people are doing.

I also know of people that used the relay to switch a Sonoff Mini that was linked to another Sonoff that’ll then switch on/off before the Node-RED days and I had a quick Google and found someone doing that just to show you what I mean by switching the Sonoff. As it’ll be nearby you should be able to just wire the AC fan into the Sonoff (instead of using that to switch another Sonoff further down the line)?

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I also went down this rabbit hole and eventually after trying a few things and spending a fair bit of cash, I found the simplest and most reliable and efficient way to cool my kit was to buy a couple of 15cm AC fans and just have them switched by a timer.

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Same here … and it moves air in my office too.


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Will definitely look into this, thanks! :ok_hand: