12v isolation switch

[linkshouse]

We finally managed to get away in our van last week, which was our first proper trip since I finished the conversion.

It was a great opportunity for a quick shakedown, so now I have list of little jobs to do here and there.

The thing that bothered me most, and what this post relates to, was that when we loaded up the inverter, using a toaster in the morning, the voltage monitor on the inverter dropped nearly to the point of shutting down, even though the BM1 was happy. This said to me that there was obviously a volt drop somewhere between the batteries and the inverter.

Now, I must confess I was a bit mean with the cable sizing but as they are very short I thought I could get away with it.

Anyway, a quick check with a meter this afternoon reveals that with the inverter drawing just over 100A I’m dropping 0.1V in the negative lead which I didn’t think was too bad.

However, when I checked the positive lead I was dropping just shy of half a volt! I split the circuit down and found that I was dropping 0.4V across the isolation switch.

Clearly this is no good.

I wondered if anyone else had experience of volt drop across their isolators and/or could recommend a more suitable isolator.

Thanks

Phill

 

[wildebus]

Is this a physical isolation switch? 0.4V across a hefty switch sounds like a lot of drop indeed. What is the spec of the switch in terms of rated current?
What about the fuse between battery and inverter? That is a point of voltage loss as well. You do have a fuse fitted? and if not, why not!

Also, when the toaster was running, how warm were the cables from battery to inverter?

 

[linkshouse]

Is this a physical isolation switch? 0.4V across a hefty switch sounds like a lot of drop indeed. What is the spec of the switch in terms of rated current?
What about the fuse between battery and inverter? That is a point of voltage loss as well. You do have a fuse fitted? and if not, why not!

Also, when the toaster was running, how warm were the cables from battery to inverter?

When I said I was a bit mean with the cables, they are still 35mm2 cables, and the total length is probably less than 300-400mm. They weren’t warm.

Yes, I do have a fuse fitted, actually there are two fuses in the total circuit, a 200A battery fuse and a separate 150A fuse for the inverter. The volt drop across each of those was less than the meter (Fluke) could read.

At circa 0.45V I’m sure the isolator is the villain of the piece. It is one of these -https://www.ebay.co.uk/itm/Isolator-Switch-Battery-Master-Cut-Off-Kill-Switch-Universal-SPARE-KEY-Boat-Van/312381775965?

I’m thinking of replacing it with one of these -
https://www.ebay.co.uk/itm/Battery-Disconnect-Isolator-Master-Rotating-Cut-Off-Switch-for-Boat-Car-Vehicles/184213674422

 

[wildebus]

When I said I was a bit mean with the cables, they are still 35mm2 cables, and the total length is probably less than 300-400mm. They weren’t warm.

Yes, I do have a fuse fitted, actually there are two fuses in the total circuit, a 200A battery fuse and a separate 150A fuse for the inverter. The volt drop across each of those was less than the meter (Fluke) could read.

At circa 0.45V I’m sure the isolator is the villain of the piece. It is one of these -https://www.ebay.co.uk/itm/Isolator-Switch-Battery-Master-Cut-Off-Kill-Switch-Universal-SPARE-KEY-Boat-Van/312381775965?

I’m thinking of replacing it with one of these -
https://www.ebay.co.uk/itm/Battery-Disconnect-Isolator-Master-Rotating-Cut-Off-Switch-for-Boat-Car-Vehicles/184213674422

Specific products that look the same will vary, but I have a couple of those first ones in my 'stock'. I'll put a meter on them and see what resistance they read.
I also have a couple of the other ones fitted in my van and I don't seem to get any noticable voltage drop from them (just did a test pulling 130A and the voltage at the battery is the same as the voltage at the inverter).

 

[linkshouse]

Specific products that look the same will vary, but I have a couple of those first ones in my 'stock'. I'll put a meter on them and see what resistance they read.
I also have a couple of the other ones fitted in my van and I don't seem to get any noticable voltage drop from them (just did a test pulling 130A and the voltage at the battery is the same as the voltage at the inverter).

I know you're "all electric" so have a bigger system (Ah wise) than me but what cross section/length cables do you have to your inverter?

Regards

Phill

 

[wildebus]

70mm2 and around 1metre end to end.

 

[linkshouse]

70mm2 and around 1metre end to end.

Aah right, so mine are about half in both aspects. Should be okay I would have thought. I did check the current rating and calculate the volt drop when I went for 35mm2.

 

[SquirrellCook]

On the Betty build I think the shortest I can make the cables from the batteries to the Multiplus will be about 4 metres. I think I’ll need to install some welding cables.

 

[wildebus]

On the Betty build I think the shortest I can make the cables from the batteries to the Multiplus will be about 4 metres. I think I’ll need to install some welding cables.

for the 12/3000 Multiplus, they say 2 x 50mm2 for upto 5 Metres
I think you are going for the new shape Multiplus though? the one thing I don't like about that is the method of cable connection - it is very hard to fit oversized cable to it you would maybe need to fit an isolation switch close to the MP as a good way to convert properly heavy cable to a gauge you can insert into the connector.

 

[Sprinter 1 cup]

for the 12/3000 Multiplus, they say 2 x 50mm2 for upto 5 Metres
I think you are going for the new shape Multiplus though? the one thing I don't like about that is the method of cable connection - it is very hard to fit oversized cable to it you would maybe need to fit an isolation switch close to the MP as a good way to convert properly heavy cable to a gauge you can insert into the connector.

Can you fit the 100,150, 200 amp fuse or isolation switch to the Inverter input ? IE no cable. I'm not on heavy electrics yet on Sea Sprinter pvc.

 

[wildebus]

There is no integral fuse holder on the Multipus for the installer to use.
You have to go Multiplus <==> Cable <==> Fuse or Switch <==> Cable <==> Battery (or whatever)

 

[linkshouse]

I've fitted the replacement isolator switch now and everything is as it should be. No measurable volt drop across the isolator and the same volt drop in both the positive and negative cable runs from the battery bank to the inverter (0.1V at 108A).

Inside the van the bar graph on the inverter controller has a five segment bar display with the top segment green, then three yellow segments then a red one to say it is nearly ready to cut out. It was dropping from green all the through the yellow to the red segment when the toaster was on, now it just drops from the green to next yellow i.e. a drop of just one segment.

 

[wildebus]

Good stuff. I haven't got round to checking mine yet. I hope yours was just a one-off fault with that specific switch!

 

[linkshouse]

Good stuff. I haven't got round to checking mine yet. I hope yours was just a one-off fault with that specific switch!

I would have thought so.

Phill