Split charge relay - fuse blows

An alchemy of sparks, copper wire and earth

Moderators: User administrators, Moderators

adrianbutter
Registered user
Posts: 40
Joined: 24 Mar 2011, 17:30
80-90 Mem No: 1

Split charge relay - fuse blows

Post by adrianbutter »

The fuse blows on my SPlit charge relay too often, and especially when I drive with a load attached - like a camping fridge plugged in to the Aux battery - so I thought I would take a proper look.

Firstly I found it odd that the Autosleeper wiring (for the internal lights and other bots and bobs came off the wire from the Relay to the Aux battery - but this is the same positive on the aux, so I guess makes no difference - you'd just expect it to be a connection to the Aux itself, rather than in the main battery well.

But here's the weird bit - the relay has been wired up wrong - for years? The earth is connected to terminal 86 (where the switched live should be) and the switched live is connected to 85 - the earth. Looking at the relay diagram - https://www.amazon.co.uk/Hella-4RA-003- ... B00H8UDS6S" onclick="window.open(this.href);return false;
- shows however this should not matter ? As 85 / 86 are the low current side of the relay, and the connections have been simply reversed.

Am I right / does any of this explain the frequent fuse blows? (Fuse is in a fuse-holder directly next to the positive terminal of the main battery) I have used a 15A glass fuse. The relay has a 20A fuse.
Ade
T25 1985 DG 1.9 (early case)

User avatar
AngeloEvs
Registered user
Posts: 1345
Joined: 22 Nov 2007, 19:22
80-90 Mem No: 4709
Location: Upwell, Norfolk

Re: Split charge relay - fuse blows

Post by AngeloEvs »

Not clear how your two fuses are connected, is one in line with the relay coil (86or 85) and the other in lne with the main battery charge feed (30) and if so which is doing what?

I use a 30A amp fuse from Main battery to Split Charge relay.

Some prefer to have the fridge connected to the ignition live side due to the high current draw of absorption type fridge elements.

Assuming your leisure battery is in generally good condition and not heavily discharged it is worth checking that the relay is disconnecting the leisure battery from the starter battery when the ignition is off. If the two batteries remain connected via the relay with ignition off then a high current will be drawn from the leisure battery when the starter is engaged.
1987 DG Karisma LPG with remodelled interior

User avatar
937carrera
Registered user
Posts: 3599
Joined: 05 Apr 2015, 19:29
80-90 Mem No: 16333
Location: N Yorks.

Re: Split charge relay - fuse blows

Post by 937carrera »

This is a good starter for how your Autosleeper should be wired - depending on year variations.

https://vwt25.blog/2016/05/13/zig-mc-2000-wiring/

All the relays and fuses are in the left/ aux battery compartment on mine, so yours could have been "amended"
1981 RHD 2.0 Aircooled Leisuredrive project, CU engine
1990 RHD 1.9 Auto Sleeper with DF/DG engine

adrianbutter
Registered user
Posts: 40
Joined: 24 Mar 2011, 17:30
80-90 Mem No: 1

Re: Split charge relay - fuse blows

Post by adrianbutter »

Good evening - thanks for the reply.

The blown fuse is on the cable from the battery - (in line fuse holder), the other fuse is part of the relay iteslf - standard JustKampers Hella unit. I've been using a 20A, as the relays are sold with a 15A fuse?

Is there a chance the charge indicator is not from the right place? I assume the charge should only begin to trickle to the Aux once the engine is started - but I note that whilst the link is dead when the key is out - it is 'connected' when I turn the key initially (before turning the starter)...
Ade
T25 1985 DG 1.9 (early case)

adrianbutter
Registered user
Posts: 40
Joined: 24 Mar 2011, 17:30
80-90 Mem No: 1

Re: Split charge relay - fuse blows

Post by adrianbutter »

Thanks '937' - I see the autosleeper diagram (my bus is 1985 - so older) has 30A fuses - so I will try this.

Just need to work out if the 'From Vehicle Ignition Switch' is correct - as surely this should only send current to Aux once engine is started. Meanwhile I'll test the van again - to see if this really is the case.
Ade
T25 1985 DG 1.9 (early case)

User avatar
937carrera
Registered user
Posts: 3599
Joined: 05 Apr 2015, 19:29
80-90 Mem No: 16333
Location: N Yorks.

Re: Split charge relay - fuse blows

Post by 937carrera »

https://www.12voltplanet.co.uk/split-charging.html

You should have a split charge system of variant "2" on the above page.

I suggest you go back to the basics of checking how your van is wired against the AS diagrams. It sounds as if the fuse you are using is smaller than AS fitted as standard, so it could simply be blowing the fuse for that reason, so step 1 could be to simply uprate the fuse to standard (note you would not be putting a bigger fuse in as a bodge in this case). I wouldn't pay any attention to what JK say.

It is of course possible that someone has modified (amended :wink: ) the wiring at the ignition switch end so that current can flow when the engine is not running (see comment in the 12vplanet regarding using the alternator output as the feed for the relay).

Swap the terminal 86/87 connections over as well - shouldn't make any difference as you say, but better to have it right.
1981 RHD 2.0 Aircooled Leisuredrive project, CU engine
1990 RHD 1.9 Auto Sleeper with DF/DG engine

adrianbutter
Registered user
Posts: 40
Joined: 24 Mar 2011, 17:30
80-90 Mem No: 1

Re: Split charge relay - fuse blows

Post by adrianbutter »

Great, thank you. I'm going to change fuses tomorrow, and then take a look at 'following' that cable to see what it is using...
Adrian
Ade
T25 1985 DG 1.9 (early case)

User avatar
937carrera
Registered user
Posts: 3599
Joined: 05 Apr 2015, 19:29
80-90 Mem No: 16333
Location: N Yorks.

Re: Split charge relay - fuse blows

Post by 937carrera »

If you have a multimeter, just put it across the leisure battery and see when the voltage changes as you go through the process of starting the van.

If it drops when cranking that would likely be bad. If it doesn't increase until the van is started that would be good :)
1981 RHD 2.0 Aircooled Leisuredrive project, CU engine
1990 RHD 1.9 Auto Sleeper with DF/DG engine

User avatar
bigherb
Registered user
Posts: 2579
Joined: 27 Mar 2008, 13:50
80-90 Mem No: 5789
Location: West Kent

Re: Split charge relay - fuse blows

Post by bigherb »

adrianbutter wrote: (Fuse is in a fuse-holder directly next to the positive terminal of the main battery) I have used a 15A glass fuse. The relay has a 20A fuse.
Glass fuses are rated at the current they will blow at, continous current is half the fuse rating, e.g a 15A glass fuse = 7.5A blade/ceramic fuses which are rated at their continous capacity (they blow at twice their rating).
1982 Camper 1970 1500 Beetle Various Skoda's, Ariel Arrow

User avatar
Mocki
Membership Admin
Posts: 16957
Joined: 29 Sep 2005, 09:27
80-90 Mem No: 428
Location: Mansfield Notts
Contact:

Re: Split charge relay - fuse blows

Post by Mocki »

it could just be your leisure battery is too flat and the system is trying to draw too big a current that the megre split charge can deliver
Steve
tel / txt O7947-137911
👀
________________

1989 2.1LpgWBX HiTop Leisuredrive Camper
1988 2.1 Caravelle TS TinTop Camper 
 

adrianbutter
Registered user
Posts: 40
Joined: 24 Mar 2011, 17:30
80-90 Mem No: 1

Re: Split charge relay - fuse blows

Post by adrianbutter »

Think I need a new multimeter.... My VDO gauge on the dash measures around 12 pre start, and 13.5 after start. Meter at the battery terminals has 10V, and the leisure batt exactly the same 10V..

Anyway, what I did get is that the line to the split charge relay has been badly fitted - it is live when the ignition key is turned, but before the cranking position (is there a name for that state - ignition on I guess, but not yet engine).

On a T25 1985 - is there a good wire to tap in to under the dash / near the fuse board? I see the advice is to take off the altenator - buit presume there is a connection at the front..
Ade
T25 1985 DG 1.9 (early case)

User avatar
bigherb
Registered user
Posts: 2579
Joined: 27 Mar 2008, 13:50
80-90 Mem No: 5789
Location: West Kent

Re: Split charge relay - fuse blows

Post by bigherb »

adrianbutter wrote:
Anyway, what I did get is that the line to the split charge relay has been badly fitted - it is live when the ignition key is turned, but before the cranking position (is there a name for that state - ignition on I guess, but not yet engine).
That is how VW wired them. It should switch off whilst you are cranking the engine to start, then back on again when the engine has started.
1982 Camper 1970 1500 Beetle Various Skoda's, Ariel Arrow

User avatar
937carrera
Registered user
Posts: 3599
Joined: 05 Apr 2015, 19:29
80-90 Mem No: 16333
Location: N Yorks.

Re: Split charge relay - fuse blows

Post by 937carrera »

adrianbutter wrote:Think I need a new multimeter.... My VDO gauge on the dash measures around 12 pre start, and 13.5 after start. Meter at the battery terminals has 10V, and the leisure batt exactly the same 10V..

Yep, I think so too :)

Looks like yours is wired as VW intended, so change the fuse (and fuseholder to accept blade fuses, same as the vehicle fusebox) and see how you go having re-run the tests.

bigherb wrote:Glass fuses are rated at the current they will blow at, continous current is half the fuse rating, e.g a 15A glass fuse = 7.5A blade/ceramic fuses which are rated at their continous capacity (they blow at twice their rating).

I didn't know that - applies to the ceramic fuses in common use through to the '80's too 8)
1981 RHD 2.0 Aircooled Leisuredrive project, CU engine
1990 RHD 1.9 Auto Sleeper with DF/DG engine

adrianbutter
Registered user
Posts: 40
Joined: 24 Mar 2011, 17:30
80-90 Mem No: 1

Re: Split charge relay - fuse blows

Post by adrianbutter »

Think I may have used poor english - or I am confused.

On my bus the signal wire is live to the split charge relay the moment I turn the key to position one; engine not started... That's not right is it? If I understand it correctly, this will connect the 2 batteries togeher via the relay. When I crank the engine the starter will pull max current through the relay, from both batteries - no wonder the fuse keeps on blowing...

Adrian
Ade
T25 1985 DG 1.9 (early case)

User avatar
Oldiebut goodie
Registered user
Posts: 7258
Joined: 18 Apr 2008, 01:19
80-90 Mem No: 11135
Location: Eastern Angle

Re: Split charge relay - fuse blows

Post by Oldiebut goodie »

The X-relay should cut that power to the relay along with headlights etc whilst cranking. ( As Bigherb has already stated)
1.6D 2019 VW T-Cross
200hp VW T6
1̶Y̶ ̶1̶9̶8̶7̶ ̶H̶i̶-̶t̶o̶p̶ ̶C̶a̶r̶a̶v̶e̶l̶l̶e̶
5̶0̶8̶d̶ ̶M̶e̶r̶c̶

Post Reply