Mysterious 20amp fuse blow (near passenger side battery)

[BongoBongo123]

So on 2 occasions I have had a 20A fuse blow over 6 months. The fuse is under the bonnet wired between the 2 batteries.

There is a small junction box called a 30A Auto Switch Combi relay (could the clue be in the 30A? ) with numerous connections 3 of which are wired:

"0v" to negative terminal of passenger side battery.
"2" via the Blue fuse that blows (20A) to + terminal of passenger battery.
"12v" which goes to the positive terminal on the other battery.

It stops the LCD control panel from working when blown which controls internal spot lights, water pump for sink etc. It seems to happen when there is nothing related to the control panel being on, otherwise I would notice it switch off when it blows. (I was thinking over current from alternator athigher speed driving for some reason as it goes between batteries)

Here is a picture (currently I popped a 15 amp fuse in just for now at risk of whatever is causing it blowing it fairly soon I imagine)



Current thoughts (pardon the pun) is like myself with the 15A fuse today someone stuck a 20A fuse in to get them out of trouble and I had simply put a new 20A in there as well last time. I might be wrong but it seems like this somehow relates to both the LCD control panel that does not work when the fuse is blown and possibly something related to leisure battery charge (given the batteries are connected via this 30A relay combi thingy.)

Any thoughts most welcome, I could just bung a 30amp fuse in but thought I might run it past you chaps first. Thanks

[rita]

The vehicle has a split charge relay system fitted using a VSR (voltage sensing relay)

This should give you an Idea what its all about.

Good Luck

http://www.instructables.com/id/Fitting ... /?ALLSTEPS

[scanner]

To put things in perspective my Willinton system has a 50amp fuse, so I reckon 20 amps is a bit on the weak side.

If your leisure battery is at all discharged it will easily try and take well over 20 amps and that is probably what is causing your fuse to blow.

[the1andonly]

Read the site posted by Rita, it does explain things well. 25A fuse rather than 30A. There should/could be another fuse at the staRter battery end of the feed. When one blows replace both. If you run the LB too low it will draw more than 30A. charge LB from mains if possible before running the system as designed. If this is a frequent problem use the split charge relay to switch a larger relay 70 to 100A eg

http://www.ebay.co.uk/itm/HEAVY-DUTY-Re ... 35db9e02d7


ps use appropriate fuses and cable if adding relay

[mikeWalsall]

Another point to take note of .. exposed wiring can now be an MOT failure ..

Five minutes and some computer 'trunking' neatens the under bonnet up ..

[scanner]

Another point to take note of .. exposed wiring can now be an MOT failure ..

Actually it says.............

Visible wiring that is insecure, inadequately supported or likely to cause a short will also result in a failure as will wires bared by damaged insulation.

Five minutes and some computer 'trunking' neatens the under bonnet up ..

However, that doesn't mean that this isn't a good idea.

[rita]

Another point to take note of .. exposed wiring can now be an MOT failure ..

Five minutes and some computer 'trunking' neatens the under bonnet up ..

Yes "nice one" you have a Pass there.

PS is there something wrong with the bonnet stay.

[mikeWalsall]

Not now .. I have fitted a new plastic support ..!!

http://www.vospers.com/parts/mazda/genu ... p-set.html

[BongoBongo123]

Thanks for the details Rita especially, I will have a read and check it all out. Thanks for the tips on wiring, the instructables looks very much like it is the same including the wire and the same VSR brand. It is an AVA full narrow side conversion so I am not sure if they did the leisure battery electrics as well. In fact I have already sured up the cabling once with cable ties and checks/re-crimps since the first fuse went. The wiring went through the last MOT in a less well attached state than it was when I got the van. It had 51 weeks MOT when I bought it, the trunking is good thing to do though.

Seems first call will be a slightly larger fuse. Will try a 25A

[Dodgey]

Your "passenger battery" (its your leisure battery) is getting over discharged. You are taking it under 10 volts (ish) which is bad for it.

This is causing the relay fuse to blown as when you start the engine there is a big current draw by the leisure battery as it is sow low.

You'll keep popping fuses as you over drain the LB. You need to

A) charge your LB with a mains charger before replacing the fuse or it will just blow again.
B) stop taking your LB below 10.8v . preferable not below 11volts .

[BongoBongo123]

Thanks Dodgey, I am not sure how that is happening because...

1) We have not been out camping for a long while (so we have not used the fridge or water pump)
2) I do nice long drives (which should charge it) and have not used the facility of the leisure battery as above

It may well have discharged once the fuse has blown if that fuse affects the circuit for recharge.

I will measure the voltage. My control panel displays the voltages of both batteries as well.

Edit : ok so yes it is 2.45volts !! (starter battery is well over 12V)

Which makes sense as it would probably not have been being charged cause for all I know the fuse may have blown 6 weeks ago.

I have a spare battery (brand new) so will give that a check and charge and put that on. The leisure battery could have been on 10 years for all I know so could be due a change, it does not look new by any means. Thanks for that info.

Ok this battery is not a deep cycle battery it is just a normal car battery which I guess is possible to damage if it runs flat.

[Simon Jones]

I think you have a knackerded battery or there is something draining it all the time. A decent battery will hold its charge for over a year as long as there is no load on it. I would connect the battery up to a proper mains charger to see if you can restore it to the correct voltage and then the original 20A fuse will be enough to keep it topped up.

[BongoBongo123]

Cheers yes seems like it. The one on there is only 75 Ah so will replace with similar we are not heavy users of the leisure battery to be honest as we tend to go away for short periods and just pack the fridge with ice packs which does the job when not hooked up saving energy.

I will get one with the +/- on the right sides as well so there is no issue with short wiring etc. Spotted a 90Ah brand new one on sale for good price and correct +/- sides for the one that is in there. And the right size to fit the tray. Jobs a good un' - peace of mind to have a decent leisure battery (it is a deep cycle one as well).

I just went for a new one cause the old one looks very old.. it must be old cause for being a 75Ah battery it is rather larger dimensions than the 90Ah one just ordered, I guess the technology is a little better with a modern battery.

I am pretty sure a new battery and fuse will resolve this niggle. Thanks for all the advice, at Christmas as well, a double hats off to you !

[Dodgey]

there is no coming back from a 2.5v battery. Even if it shows a charge it'll still be knackered.

To get that low there must be something draining it. It won't go that low on it's own. Worth finding out what is doign that.

Happy Christams to you too

[BongoBongo123]

Hmm.. everything appears to the eye to switch off when ignition goes off, there is no alarm or immobilizer LED thing flashing, no lights on radio etc. Temp alarm I pull out of ciggy lighter at journey end.

I will have to put the new battery on, operate normally and test voltage every week and check the fuse regularly to see what is happening.

I guess I can see if there is any current flowing in series in various states of "off". I would expect to see zilch when engine off and zilch unless I switch something connected to the battery through the control unit, i.e. pump, fridge (I think I will go out and double check that the fridge is definitely off first !). If some of the cells are kaput I guess it would never charge or hold charge properly.

Edit : Ok the culprit for battery drain is the fridge, I left it on the lowest setting thinking it was in off position, why I do not know we rarely use the actual power and use it as a cool box with ice packs...looks like I can have the old leisure battery as a spare. Live and learn !