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TOPIC: Hello and can you help what are relays for?

Hello and can you help what are relays for? 1 week 20 hours ago #455984

  • ericmark
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I have a Odyssey from the Explorer Group under the left hand bunk on back of battery box is the charger and a relay box the latter with a row of blade fuses, the printed circuit is marked PCB-147-MD and an internet search shows these have been replaced with PCB-184-MD when we bought the caravan everything was working, but before we even got it hitched to car we lost most of the 12 volt electrics, as a quick cure the dealer fitted an in line fuse holder and everything started to work again.

However the main switch did nothing, and having had a flat battery, I decided I should look at the problem. On removing the in line fuse the main switch started to work, and I found a slack top fuse holder which was likely the reason.

However I noted a second in line fuse which when removed the lights stopped working. I though it was a good idea to fix this too. There are two 10A fuses marked Lights 1 and Lights 2 which are dead both sides of the fuse, these seem to connect to a bank of 5 relays on the board.

Counting down number 4 is main isolator and 5 is for water pump, however not a clue what 1, 2 and 3 are for? I am not getting a supply to the coils of the top three relays, and it does seem as if these have something to do with lights.

I found a circuit diagram but it only shows 4 relays and I have 5 and colours of wires are different so clearly wrong one. I am slowly working things out, but I simply can't think why the relays are there, if I know that I have a chance of finding what is wrong.
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Hello and can you help what are relays for? 1 week 19 hours ago #455988

  • ProfJohnL
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Hello Eric,

Welcome to the forum.

I could be wrong, but is seems a previous owner may have modified the electrics, and that will make it very difficult for us to offer any copper bottomed advice.

Your post suggest you do have some skills with electrics, so I suspect you will either need to persevere and work out whats happening yourself, or maybe admit defeat and call in an assured professional.
Unless I use quotes, All advice and opinions given are my own and are given in good faith. Never act on anything you read on a forum unless you can validate and verify its source and content.
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Hello and can you help what are relays for? 1 week 10 hours ago #455994

  • ericmark
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Yes I am a professional but not worked on modern caravans. The relay box is standard, a motor mover has been added but that should not affect the operation of the relay box.

I will guess that one reason for the box is you need two engine running feeds from the car but the second 7 pin socket only gives one. So a relay trigured by engine running will use the perment supply as the second engine supply. However although that could affect battery charging and 12 volt fridge supply can't see why that should affect the lights.

My next move is to emulate a car being connected.

However if I knew why the box is fitted, it would help tracing fault. Some bits make sense like master switch having a relay, but I am sure the water pump switch could take water pump load, can't see why a relay is fitted? Just something else to go wrong.

Clearly caravan designers don't agree.

One thought is when on car power maybe only half the lights are active? Or of course same if battery charger not active. The replacement has diodes so could do that, but the one fitted just relays and fuses all relays single pole so really scratching head as to why fitted, internet seem to show box made in USA so maybe something special over there?
Last Edit: 1 week 10 hours ago by ericmark.
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Hello and can you help what are relays for? 1 week 8 hours ago #456004

  • Thingy
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My first step would be to obtain the schematic for the wiring and start by looking what is different or not working, failry simple with a decent multimeter.
Shogun 3.2 SG3 (197) tugging Stirling Continental 530
(Im a caravanner - if it aint broke -it will be tomorrow.)
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Hello and can you help what are relays for? 1 week 7 hours ago #456016

  • ericmark
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Slowly working it out, I got a wiring diagram however it shows 4 relays and I have 5 and wire colours don't match. I have progressed.

Front 5 lights are separate to back lights, and they with swap from external battery to internal battery, as I connect my test battery you see front lights dim as only 7 Ah and not being charged and they go off with master switch, the rear lights only work when the in-line fuse is in and always from caravan battery and unaffected by master switch.

When on external battery the Lights 2 fuse becomes live, but not with internal battery.

Relays counting down first two work when fridge supply made live red/black and third centre when car supply made live green/white and the black neg does not seem to be connected to white neg. Other than relays operating the red/black supply does not seem to do anything, clearly with 7 Ah battery not going to try running fridge.

The green/white supply momentary switches off supply so if master switch is on then radio auto fires up each time I switch the car supply on or off.

So I still have Lights 1 fuse with no supply. I will guess caravan around 2004 but still scratching head. We are looking to get new tow car, and when we get it then we will get both sockets wired, I don't want problems as a result, for example radio auto turning on.

Also had a flat battery last year, I had assumed turning off the large isolator by the battery would insure there was no drain, however it turns out this only turns off the motor mover, it is so easy to miss a light, specially the outside one, really want everything to go off when master switch is off.

Not sure when the master switch relay will drop out, but I would hope even if master switch left on, the relay would drop out before battery that flat that a smart charger will not recharge it?
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Hello and can you help what are relays for? 1 week 7 hours ago #456018

  • ericmark
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Picture of what I have worked out so far.
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Hello and can you help what are relays for? 1 week 5 hours ago #456021

  • ericmark
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Found the fuse labelled Ignitions is actually lights, because the bypass fuse was in I missed finding the blown fuse by simple testing. as fed from both sides, there was a 2A fuse feeding around 6 lights no wonder it ruptured.
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