What is this black box for in my electrical cupboard

TobyQuest

TobyQuest

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Jap Import Nissan4x4
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Hi all,

Power from my leisure battery goes into this black box and comes out of it to my fuse block. Ive run a switch to this black box and when I switch the switch off, ALL the electrics to the leisure stuff stop working.
But I have no idea what the box does (shown in the centre of the pic)
It came as standard.

Please help. Its a 1993 van, so the tech may be somewhat old fashioned if that helps
 

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I can't help with your question but hopefully someone will be along soon (y)
 
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Ask the previous owner?

One possibility is a manufacturer's label underneath or on the side we can't see that would help explain what it might be.
 
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In the old vans all the electric in the back used to go off when you started the engine.
Has someone, somehow by passed this as a lot did.
Don't know what the actual box is, but it could have sort of relay or something in it.
 
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Cant ask the previous owner as it was sold by a dealership in Japan and the guy speaks only Japanese, so ill see if theres a label or any wording and let you know.
The blue box was a battery charger and converted AC to DC but ive stripped that out and chucked it, because it would have been a Japanese battery charger converting from 100V AC to 12V DC rther than 220 to 12V.
 
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If it has three wires going into it, then probably a Battery Master which is designed to send a small charge to the engine battery when leisure battery is near full charge.
 
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It's hard to see where the wires go in the photo, but it's common to have a box that contains the split charge relay and the fridge relay. These connect the leisure battery and the fridge to the alternator when the engine is running. Also some MHs (mostly British ones) have a relay that switches off all the habitation electrics when the engine is running.
 
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On the top righthand side you will find a slot. That is where you put your shilling in.😂

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OK today i took it all apart and here's the photos :D
20200701_235037.jpg
 
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Not sure, but I'd say the circuit board reads a voltage and switches a relay or two. Maybe a voltage sensitive relay for charging the leisure battery, or a battery protect cutoff that disconects if the voltage gets too low. I can't see where the thin red wire from the separate relay goes to.
 
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autorouter said:
Not sure, but I'd say the circuit board reads a voltage and switches a relay or two. Maybe a voltage sensitive relay for charging the leisure battery, or a battery protect cutoff that disconects if the voltage gets too low. I can't see where the thin red wire from the separate relay goes to.
Click to expand...
I know the boiler doesnt work when the engine is running. Could this be the gadgetry for that and if so presumably more jobs it does than only that?

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I guess that its a voltage sensing device perhaps to act as a split charge relay. The black of the big relay is on the common rail so that suggests that perhaps the bigger relay is controlled from the pcb.
The numbers of IC1 and IC2 would be a clue, suspect Ic1 is something like an LM317 voltage reg.
I did say previously thats its all a learning curve!
TH 9102 is the pcb number, doesnt mean anything unless you knew the maker
Mike
 
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It does have a separate unit elsewhere that is a diode splitter.....this works in a similar way as a split charge relay.
 
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IMG-20200703-WA0016.jpg

In black ink on the other side it has the number 291 on it. Does that help identify?

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On that 2nd pic on post 11. You’re finger is just covering the bottom wording which will be either another n/o or n/c?
 
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It's a dual comparitor made by Toshiba then 👍 super useful chip, but sadly without a circuit diagram we don't know what it does here for certain 🤔
 
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Richard and Ann said:
It's a dual comparitor made by Toshiba then 👍 super useful chip, but sadly without a circuit diagram we don't know what it does here for certain 🤔
Click to expand...
I agree, but it's clear that it switches a relay after comparing two voltages. There's an LED, that presumably switches on when the relay is on. You can probably hear a quiet click. I mean the small relay with the transparent cover, attached to the circuit board. It's a double-pole double-throw relay, but only one throw is wired, and only one of the poles has wires connected (COM 2 and N/O 2).

Can you confirm that the wire from N/O 2 goes to the +12V terminal?
Where does the wire from COM 2 go? To the big black relay coil or out of the box?
Where does the thinner of the three red wires on the big black relay go to? COM 2 or out of the box?
TobyQuest said:
Ive run a switch to this black box and when I switch the switch off, ALL the electrics to the leisure stuff stop working.
Click to expand...
Where exactly did you wire the switch? Between SW1 and SW2?

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I will take a picture tomorrow and investigate the answers to your questions.

In the mean time this is my approximate wiring that Ive been able to figure out so far.
NJ WIRING SCHEMATIC.png
 
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I'm having a quick look now...
The thinnest red wire comes in from the battery to this kind of 3 socket bus bar and then diddly onto the black box to DC12v+ marker.

The thickest red wire also comes directly in this way and goes to the black relay box to the right hand side position.

SW2 white wire is a positive wire that goes directly to my switch on my blue led switch panel and the negative comes out of that switch and goes ditch back into the black box at SW1

DC12v+ sticker has a 2nd red wire that goes from there and connects into N/O2

Dc12v- has 2 wires. One goes out of the box to this bus bar where all appliances are grounded.
The 2nd wire connects to the relay in the bottom position.

Com2 has a thin red wire that connects to the relay in the left side of it

Finally the thick red wire comes out of the relay and powers my main fuse block that all my appliances are connected to.... Cabin lights, roof fan, rear switch panel, kitchen lights etc
 
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The big black relay is a power relay. When 12V is applied across the coil through the thin wires, it switches the main current through the thick wires.

The 12V to the coil comes from the +12V terminal, and is switched by the transparent relay on the circuit board. The 12V goes in to the N/O (= Normally Open) terminal, and out through the COM (= Common) terminal.

The circuit board looks like it switches a low-power (transparent) relay when two voltages differ by more than a preset amount. The low-power relay switches the high-power relay, which switches all the habitation functions on and off. So the whole box is a Voltage Sensitive Relay (VSR).

Why does it switch the habitation functions on and off? That's the question. If the trigger voltage is set low, it cuts off the habitation functions when the battery voltage gets too low, so it's for battery protection. If it cuts off when the voltage goes high, it might be intended to switch off when the engine is running. I doubt it's the second, because that's just a British thing, no-one else does it.
 
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Pull the big red wires off the relay (tape them up) and see what changes, then you know what is does, simple 👍
 
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