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HTB

Member Since: 24 Mar 2013
Location: Surrey
Posts: 71

2012 Defender 90 Puma 2.2 HT Buckingham Blue

Switched Bluesea fuse box - Relay size?

I'm adding a number of USB plugs and other power feeds to my 2.2 Puma, so seems sensible to add a Bluesea fusebox to my battery box and have it switchable so it doesn't drain the battery if I leave kit plugged in when the vehicle is parked. Potentially I'll have a Garmin GPS, windscreen cam, and 3 USB chargers all pluggged in. Appreciate this isn't a massive draw, but don't want to underspec the main feed to the fuse box.

I've been searching through the forum but can't find a recommendation of the size of relay (AMPS) I need to switch power to the fuse box - or indeed a circuit diagram or picture to show me what to do. I know I've seen diagrams out there - I just can't seem to locate them now and am going round and round in circles.

So, what size relay and cable should I use to carry the 12v power to the fuse box? I'm thinkinhg something like this https://www.autoelectricsupplies.co.uk/p/1...-and-break

Planning on using 25mm sq battery cable to run from battery, to relay and then to fuse box.

Any advice much appreciated.
Thanks,

Harry

5th Aug 2023 2:27pm

Martin
Site Admin

Member Since: 02 Apr 2007
Location: Hook Norton
Posts: 6605

2015 Defender 90 Puma 2.2 XS CSW Montalcino Red

100A relay and 170A rated cable seems overkill for a few USB chargers, by a factor of 50 or so!!

Quote:
and other power feeds

What other devices/kit are you going to (or potentially going to) be supplying from this fuse box?

1988 90 Td5 NAS soft top

2015 D90 XS SW

5th Aug 2023 4:28pm

HTB

Member Since: 24 Mar 2013
Location: Surrey
Posts: 71

Yes, having had a proper think about it Martin, I can certainly see its all a bit over the top.

Other than the USBs and an old school cigarette socket for a cool box I'll also be charging (or at least topping up) a 700W Bluetti power station, running a dashcam and Montanna 700i GPS, so nothing excessive.

5th Aug 2023 5:08pm

Martin
Site Admin

Member Since: 02 Apr 2007
Location: Hook Norton
Posts: 6605

The Bluetti appears to charge at 100W (~8A).

Coolbox would be around 50W.

Your other USB, camera and GPS loads will significantly under 10A total.

So looking at approx 22A with the generous USB etc load.

Go with a standard automotive (40A) relay. The supplier you linked to above has a neat fused relay - code 140202. Fit this as near the battery as possible so the fuse protects your wiring to your new fuse box.

3mm² thinwall cable is rated at 33A. I would go with this between the battery

What are you going to be triggering the relay from?

1988 90 Td5 NAS soft top

2015 D90 XS SW

7th Aug 2023 2:28pm

HTB

Member Since: 24 Mar 2013
Location: Surrey
Posts: 71

thank you.

I haven't decided on the switch trigger yet. I have heated seat looms and the heated windscreen loom to fit too, so hoping to utilise space on the fuse box under the drivers seat, and pick up a trigger from there...

8th Aug 2023 10:29am

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