# vehicle battery



## 90725 (May 1, 2005)

I bought a used Sundance 500 (1999 T reg) in March and absolutely love it. No problems reversing up hill or anything like that and amazingly low fuel consumption. One question that I can't find answered in the handbook is whether the mains hook-up charges the vehicle battery in addition to the leisure battery. I would welcome advice on this.


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## philoaks (Sep 2, 2008)

Don't know about the Sundance specifically but if not there is an easy mod that has been documented in MMM.

The mod can be carried out by any competent person and basically consists of linking the vehicle and leisure batteries together with a fuse in the link. 

When you want to charge the vehicle battery you fit the fuse and then switch on the charger. When finished you switch off the charger and remove the fuse.

Should you forget to remove the fuse and attempt to start the vehicle the high current drawn by the starter motor will blow the fuse preventing any further damage (spare fuses should be carried).

I can't remember when the article appeared in MMM but someone out there may know.


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## DABurleigh (May 9, 2005)

I can't answer your specific question (some motorhomes do, some don't) but there are many ways around it, Battery Master etc, and this is the one referred to:
http://www.motts.dsl.pipex.com/BRIDGING FUSE.htm

Dave


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## SwiftGroup (Jun 27, 2007)

*Battery*

rmsigrist

By use of the battery selector switch on the control panel, charge from the on board battery charger can be directed to the leisure or engine battery.

Regards
Kath


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## Gonewiththewind (Nov 17, 2007)

philoaks said:


> Don't know about the Sundance specifically but if not there is an easy mod that has been documented in MMM.
> 
> The mod can be carried out by any competent person and basically consists of linking the vehicle and leisure batteries together with a fuse in the link.
> 
> ...


Mine has a similar set up but with a rotating red switch. What damage is done by leaving the batteries connected? as I have done this regularly. 
Was never explained as I think it was a retro fit.
Don


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## philoaks (Sep 2, 2008)

Once the engine is running the batteries are effectively connected together by virtue of the split charge relay. As soon as the engine is stopped this relay releases and the link between the two batteries is gone. 

By having them connected together via your switch arrangement, when you attempt to start the engine the load is shared by both batteries. This means that the starter motor will be trying to draw a very large current from your leisure battery. 

For this to be a safe installation the cables (both positive and negative) onto the leisure battery would need to be at least the same size as those connected to the engine battery (if not bigger, as the leisure battery is probably further away from the starter motor). If the cables aren't of sufficient size then pulling such a large current would cause them to overheat with possibly disastorous consequences. The mod mentioned earlier using a fused bridge is done like that for this reason. The high current will immediately blow the fuse and prevent any overloading of the cabling.

Another point to bear in mind is that leisure batteries sometimes are not standard lead/acid batteries but are "leisure batteries". These are not designed to produce the very large currents demanded by starter motors and could be damaged by that sort of use.


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## Gonewiththewind (Nov 17, 2007)

So am I right in thinking that this switch should only be used if the vehicle battery needs the extra power (ie) Jump Start.
Don


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## philoaks (Sep 2, 2008)

Without seeing the way it's been wired it's difficult to be sure but personally I would only switch it so that the batteries were linked when you want to charge the vehicle battery from the onboard charger.

Having it linked when attempting to start the vehicle could result in the overheating as mentioned earlier.

If it was mine I think I would replace the switch with a removable fuse as in the linked article.


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