# What size fuse for my battery link



## Pudsey_Bear (Sep 25, 2008)

I'm in the middle of putting a link from the Leisure batteries to the engine battery (Clive Mott style with a twist) I've gone from the +ive on the engine battery to an illuminated switch on the drivers door side of the dash ( so I see it getting in and turn it off) with fuse holder, and from the switch through a fuse holder to the leisure battery clamp.

I'm not sure what size fuse to use, both under the bonnet and inside the cab, any ideas.

Kev.

PS I got a lovely proper mountable fuse holder which takes 4 fuses, so plenty of parking space for spare fuses, for when I forget to disable the link before starting the MH up, I also found a light which is designed to fit in the gas locker, so you can see to bu66er about in the dark without a torch or having an incandescent bulb in with an explosive gas, (not good) fits in the gas locker but is sealed from inside, with a rubber gasket.


----------



## macone48 (Mar 14, 2006)

Kev,

In two words..........DO NOT.

I've no association with Van bits, but my M/Home came with a "Battery Master."

This charges the engine battery from the habitation batteries/charger when the habitation ones have reached near full charge. Plus it can discharge slowly back to assist Habitation side - all done electronically.

Without saying....I told you so.........one day you will forget and you'll have flat batteries. For around £70 just let electronics do it.

Read this link: 
Battery Master

Trev


----------



## Fatalhud (Mar 3, 2006)

What is the link for Kev, 

In my gas locker I stuck one of those cheap battery powered LED units.

Alan H


----------



## Pudsey_Bear (Sep 25, 2008)

Fatalhud said:


> What is the link for Kev,
> 
> In my gas locker I stuck one of those cheap battery powered LED units.
> 
> Alan H


May I respectfully suggest you remove it, switch sometimes = sparks, mixed with gas, not good, = no more Alan H, and we don't want that do we.

link is to charge engine battery when on EHU.

Kev.


----------



## Pudsey_Bear (Sep 25, 2008)

macone48 said:


> Kev,
> 
> In two words..........DO NOT.
> 
> ...


Thanks Trev, maybe I'm missing something or (more likely) I didn't explain enough, it is simply a wire going from one battery to another, no more, but while switched to connect it charges the engine battery, if I do forget, it blows a small fuse when I try to start the engine, If left on with out EHU it will discharge all batteries at the same level/speed (I think) so I don't see a problem, but if you do, please expand so my old tired brain can grasp it, then I'll be a little better informed, but whatever there's no way I'm spending £70 on a box to do what I can do with a little foresight and check before going away, my engine battery has only gone flat once this year, when I left a light on Doh.

Kev.


----------



## macone48 (Mar 14, 2006)

Kev,

I don't need to explain anything further.

I know what you intend to do - IMHO just so penny-pinching after how many £1000's u paid for you M/Home.

If you don't want to spend a little, I won't waste my time and advice further.

But when you flatten the battery *again* - just PM me so I can go Na de Nah, de Nah..............!!!

Trev


----------



## Fatalhud (Mar 3, 2006)

Hi Kev 

As for the light 
1 - I like to live life on the edge
2 - I left it on and the batteries went flat, then manky
3 - it fell off after about 2 months

:wink: :wink: :wink: 

As for your link
I would rate it at a suitable size to protect the cable and switch

Or you could put a relay that when the ignition was turned to on, it isolated the cable before turning the starter motor 

Alan H


----------



## backaxle (Nov 6, 2006)

There is a simple way to charge your engine battery when on EHU and that is to plug your battery charger into a mains socket ,within the van, and plug the other end into your cigar lighter,or attach the clips to the engine battery.This way, you are charging both batteries at once.When you unplug from the mains the charger stops. Having said that someone will come along and knock it  
Nev.


----------



## Pudsey_Bear (Sep 25, 2008)

macone48 said:


> Kev,
> 
> I don't need to explain anything further.
> 
> ...


Eh what's that all about, if you don't have the pennies you can't spend them, we're not all working you know.

Kev.

PS £70.00 is more than a weeks money on jobseekers, if I was getting it, which I ain't


----------



## Pudsey_Bear (Sep 25, 2008)

backaxle said:


> There is a simple way to charge your engine battery when on EHU and that is to plug your battery charger into a mains socket ,within the van, and plug the other end into your cigar lighter,or attach the clips to the engine battery.This way, you are charging both batteries at once.When you unplug from the mains the charger stops. Having said that someone will come along and knock it
> Nev.


I won't be the one to knock Nev, seems a good idea, if there's a down side, it's having another appliance which may get warm, inside the MH unattended, but excellent lateral thinking, now which side of the dash shall I nail this socket to.

Kev.


----------



## Pudsey_Bear (Sep 25, 2008)

Fatalhud said:


> Hi Kev
> 
> As for the light
> 1 - I like to live life on the edge
> ...


How would I wire the relay Alan, it's ages since I've done one and that was to power some spots, not a clue how to do it the other way IE to remove a link.

I have thoughtfully provided a relay shown set up for spots, so it might make explanation a bit more gooder.

Kev.


----------



## Fatalhud (Mar 3, 2006)

Your spots are wired normally open contact

You get a relay that you can wired normally closed, 
When the ignition comes on, it powers up the relay and opens the relay, killing the link

Alan h


----------



## raynipper (Aug 4, 2008)

Kev.
Already fitted by the previous owner to my van under pass seat.
A small 3 stage charger bought from Lidl's for about £15 (£40 on e-bay) connected to the engine battery but left permanently plugged into a mains outlet in the van.
So when on EHU charging the leisure batts this little 'gizmo' just topps the engine batt as and when necessary.

Ray


----------



## Pudsey_Bear (Sep 25, 2008)

Fatalhud said:


> Your spots are wired normally open contact
> 
> You get a relay that you can wired normally closed,
> When the ignition comes on, it powers up the relay and opens the relay, killing the link
> ...


Ah never come across one of those, so my relay in the shed's no good to me then. bummer.

Kev


----------



## Pudsey_Bear (Sep 25, 2008)

raynipper said:


> Kev.
> Already fitted by the previous owner to my van under pass seat.
> A small 3 stage charger bought from Lidl's for about £15 (£40 on e-bay) connected to the engine battery but left permanently plugged into a mains outlet in the van.
> So when on EHU charging the leisure batts this little 'gizmo' just topps the engine batt as and when necessary.
> ...


again a neat idea, and thrifty too, shame the chargers aren't currently (geddit) on sale.

Kev.


----------



## olley (May 1, 2005)

As has already been said, you need to size the fuse to which ever of the wire or switch has the lowest rating or below.

Olley


----------



## Fatalhud (Mar 3, 2006)

A lot of relays have the option to wire either normally open or normally closed
Nothing new

If you look at the photo on the link
terminal 30 is common
terminal 87 is normally open
terminal 87a is normally closed


Alan H


----------



## Pudsey_Bear (Sep 25, 2008)

Nearly all done now, Switch mounted, but removed the earth wire to illuminate it for now, instead I've mounted a fancy alarm LED which is far more visible from the drivers seat, it only comes on when the switch is activated, and it doubles as a visible alarm warning as far as anyone waking past is concerned, it is alarmed but there are no visible signs that it is so.

Just need to get under the seat to connect to the leisure battery.

Diagram (sorry Crap diagram of how it's wired up) no where near as pretty as Clives version but should work better for me, and I'd not have been able to do it without his to work from, as I didn't know it was possible, so Thanks Clive for the inspiration.

Kev.

PS Slightly off my own topic, does anyone know how to get rid of those scratches to the right of the switch.


----------



## pippin (Nov 15, 2007)

*It is very dangerous the way you have wired it.*

You should fit another fuse by the engine battery +ve.

As shown, there is nothing protecting the wire from the engine battery +ve to the dash switch, LED flasher and the fuse board.


----------



## Spooky_b329 (Jan 24, 2009)

I can see a few issues with this set up.

Firstly, when you flick that switch, if the batteries are at different states of charge, such as leisures at 70% and starter (battery) at 95%, or starter at 50% and leisures at 100%, you will get a considerable current surging through your wiring and switch as the batteries try to equalise the charge between them. The bigger your batteries, the more current can flow.

I have a 110ahr starter and two 85ahr leisures, for this set up I need a 25mm cable fused with 80amp fuses to safely connect the batteries directly. (via a 200amp voltage sensing relay) As you will see below, I have used 35mm cable in case I need to double the size of my battery bank.

Second, you need to fuse your link cable at both ends, as close to the battery as possible. The reason is your cable is live from both ends, the fuse can blow but all that will do is disconnect the batteries from each other, if the cable has shorted out on the bodywork, it will get hot, melt and catch fire! It needs to be fused at both ends!

Third, your illuminated switch. What current is it rated at? The only switches I could find that are able to cope with anything near 80amps are isolators (red key type) and heavy duty relays. The switch could melt under load.

Sorry to be the bearer of bad news, but it would be much easier to use your new wiring to connect to a mains battery charger which will have a regulated output. Don't connect both leisures and starter to the same outputs of your main charger as this again is simply connecting both batteries, allowing large amounts of current to flow between the batteries! Even with a normal charger, I suspect your strobing LED won't be able to cope with the current passing through it.

This is my set-up for comparison, you are effectively attempting the same thing with a 5 amp fused link.


----------



## dipsticks (Aug 2, 2007)

I have just put a 5 amp circuit breaker and a diode between my auxilliary batteries and starter battery (on the Clive theme) and it seems fine. (the volt drop forward through the diode is only 1%)

It allows the solar to charge all the batteries, won't allow me to drain the starter battery and will trip out and be re-settable if the current exceeds 5 amps. I can switch it on or off as required too.

Found all the bits in the garage so a freebie really.

Please tell me if I am wrong.

Pete D


----------



## Pudsey_Bear (Sep 25, 2008)

pippin said:


> *It is very dangerous the way you have wired it.*
> 
> You should fit another fuse by the engine battery +ve.
> 
> As shown, there is nothing protecting the wire from the engine battery +ve to the dash switch, LED flasher and the fuse board.


Absolutely right Pippin, and I have, I knew I'd left something out, I tend to fuse as I go and it was last year when I did the under bonnet part and so forgot it.

Thanks for reminding me, I'll see if I can change the drawing in an edit.

Kev.


----------



## geraldandannie (Jun 4, 2006)

*cough* CAK tanks BCM12 £24.91

I'm sure it's nowhere near as good as a Battery Master, but it seems to do the same thing. I don't have one, but I'm sure someone on here will have.

Look at their 'carbon neutral' catalogue :: here ::, page 81.

PDF price list :: here ::

Gerald


----------



## artona (Jan 19, 2006)

http://cgi.ebay.co.uk/DUCATO-SPLIT-...LM%2BLA&otn=5&ps=63&clkid=8551523731635424383

another one

stew


----------



## Pudsey_Bear (Sep 25, 2008)

Spooky_b329 said:


> I can see a few issues with this set up.
> 
> Firstly, when you flick that switch, if the batteries are at different states of charge, such as leisures at 70% and starter (battery) at 95%, or starter at 50% and leisures at 100%, you will get a considerable current surging through your wiring and switch as the batteries try to equalise the charge between them. The bigger your batteries, the more current can flow.
> 
> ...


Thanks for the explanation and drawing Spooky, however I'm not qualified to comment one way or the other, I simply took Clive Motts idea and modified it to suit my needs, and it's essentially the same thing, Clive does a lot of electrical advice on here and is copied by many, but your explanation does make sense, but the two are poles (sorry ) apart, so I'll await comment by other sparky types before making the final link to the leisure battery.

Assuming that my set up is flawed would a 5 amp fuse not solve any issues by just blowing, the switch used is this one

On thinking about it, wouldn't the batteries be about the same when switched to link, (just showing my lack of knowledge) as it would be at the end of a run usually and both should be charged up.

Kev.


----------

