Adding a third battery - wiring size (1 Viewer)

[veevee]

Currently have 2 habitation batteries and replacing them with 3 new ones. The Elektroblock is protected by a 50 A Maxi fuse close to the 2 existing batteries.

To wire these new batteries in parallel I'm thinking of using 10mm2 cable with a length of around 70cm for each cable to the third battery, does that sound about the right size or should I go larger?

A few weeks after installing the batteries I'll be adding solar to the charging system with a Schaudt MPPT solar regulator and it's designated connecting points into the Ebl, would that alter the method of wiring the 3rd battery?

Thanks a lot

 

[scotjimland]

With that length of cable, I would use the same size cable as feeds the other two batteries,10mm2 sounds fine.

A third battery won't affect the solar charger wiring .. but you should consider fitting the LS 1218 additional 18amp charger to enjoy the same charging rate you have for existing pair.

 

[JeanLuc]

Scotjimland makes a good point. When Hymer fitted three habitation batteries as standard in the large S-class models of the same vintage as your B680, they fitted the LAS1218 supplementary charger too.
The supplementary charger only has any effect on mains hook-up of course.
The 12v feed from the LAS1218 plugs into Block 7 on the face of the EBL99 and the unit has a 230v 'kettle lead' to feed it which will need to be piggy-backed off the existing kettle lead going into the EBL. Not exactly sure where you would fit the additional charger though as there is not much room under the driver's seat next to the EBL (assuming yours is LHD) and you may want to fit the LRM1218 there as well.

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[veevee]

Thanks Jim and Philip

The EBL101 is the unit fitted if that would make a difference and yes it's LHD.

The idea is to fit the LRM1218 against the rear of the dinette seat (facing forward) close to the floor and to the rear of the driver's seat, and not even try to fit that under the seat.
Had an electrical problem of chaffing charger cables (this MH has never had any work done on it as no accessories fitted at all and extremely low mileage, so the chaffing problem along with a second one about to create a problem was created by Hymer) about 3 weeks ago and couldn't get at the source very quickly as had to unbolt the seat. So not a fan of the under seat locations.
The area low down behind the driver's seat is a relatively 'dead' area so a good location for extra equipment.

I don't dispute what you are saying about the 3 battery 'S' class and the LAS1218, but I don't quite understand why an extra charger is required as the EBL101 already has an 18A output. I also don't quite understand how they would side by side either.

Thanks again, really appreciated

 

[scotjimland]

Contrary to popular belief you can't just keep adding batteries and expect them to be charged properly.. I've read on here and elsewhere than an extra battery will only increase the total charge time.. this is only true to a point, there is a limit and an optimal battery bank size for any charger.

When batteries are connected in parallel ( assuming identical size and type) the charging current is split equally between them..

thus:

An 18A Charger with 2 batteries in parallel will put 9 amps into each

If 3 batteries in parallel the current is then 6 amps to each

if 4 (including starter) the current is 4.5 amps

The EBL 101 has a 180Ah limit, you should make an allowance for the Starter battery capacity when calculating the bank size.

So while it is not essential to fit the aux charger is is certainly desirable.

 

[veevee]

Beautifully explained Jim, and thank you for that.

Years ago on a different MH we had less panel output than we have now to fit, but 2 very large hab batteries (can't remember the capacities but physically a lot larger). The regulator wasn't anywhere as efficient as the current MPPT ones are.
We were full timing for 3 years and what we found was we didn't use too much of the battery capacity and even if we did (often spent the winters in N Africa so that sometimes mitigated the need for heating) we moved a lot so vehicle charging added to the available solar, only saw a hook up maybe every 2 weeks or so. The solar output managed about 70 ish % of our charging as we were constantly just topping up, and a 500km drive did the rest.
If we had drained the batteries completely or nearly so on a regular basis then I do understand the need for enough 230v charging capacity, but it wasn't required in our previous life.

That said I don't think we'll travel in the same manner in the future but we may full time again, we may even try some less frequented places too, but I think we would see camp sites or aires with power more frequently so what you write now is quite relevant possibly.

To add to what you have written the 3 Varta wet batteries are 90Ah each, so 270A in total. Add to that the 100A starter battery and maybe the EBL101 will be overwhelmed.

Last, if in a couple of years we decide to head off for the 'Stans' or maybe the US and Canada I want to try to keep the MH as simple as possible, always believed in 'keep it simple' for just about everything, so I may see what happens when the solar is fitted and how it performs in relatively sunny France before thinking of an additional charger, does that sound like a plan?

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[scotjimland]

Yes, I would agree. I have 2 x 80ah GELs with 160 watt solar, with the LR1218 charge controller. This has been plenty for us.. never required a hook up last year.. but we all have different needs and expectations.. try it and see, can always upgrade if required.

Winter of course is a different proposition, unless you are driving every couple of days you need an EHU in Northern Europe.. no amount of solar or batteries would keep you going..

 

[maxi77]

Contrary to popular belief you can't just keep adding batteries and expect them to be charged properly.. I've read on here and elsewhere than an extra battery will only increase the total charge time.. this is only true to a point, there is a limit and an optimal battery bank size for any charger.

When batteries are connected in parallel ( assuming identical size and type) the charging current is split equally between them..

thus:

An 18A Charger with 2 batteries in parallel will put 9 amps into each

If 3 batteries in parallel the current is then 6 amps to each

if 4 (including starter) the current is 4.5 amps

The EBL 101 has a 180Ah limit, you should make an allowance for the Starter battery capacity when calculating the bank size.

So while it is not essential to fit the aux charger is is certainly desirable.

Certainly an 18amp charger will take more time to fully charge even 2 batteries just a fact of life. It all depends how fast you need them charged. The starter battery should be out of the equation as it only gets used to start and is mainly recharged by the alternator. One of the main worries is the suggestion in some places that Electroblocs have a problem charging more than 180AH worth of battery. The only explanation I can think of is that if the extended charging time for more Ampere hours causes components in the charger to overheat. If this is the case a bigger charger is clearly needed

 

[scotjimland]

One of the main worries is the suggestion in some places that Electroblocs have a problem charging more than 180AH worth of battery. The only explanation I can think of is that if the extended charging time for more Ampere hours causes components in the charger to overheat. If this is the case a bigger charger is clearly needed

that is the advice from Schaudt, and other charger manufacturers .

Ideally the Battery Bank size should be no more than 10 times the charger output. i.e. 18A x 10 = 180ah.

Schaudt aslo state the minimum for the EBL is 55ah.

the reasons are not because it would overheat the charger, it is about the optimal time to recharge the batteries.

Further reading with general rules..

http://www.tnbpowersolutions.com/sites/default/files/webfm/resources/upload/Industrial UPS/Battery Chargers/Application Paper/CYB_Proper Charger Sizing for Utility_APPLICATION PAPER.pdf

For the most part, batteries will not accept a charge, regardless of how much current is available in less than about 8 hours and will not recharge from a practical standpoint in more than 24 hours, using typical constant potential-current limited charging techniques. While this comment is a generalization it is also a safe bet. If you want to recharge a battery either faster or slower than the 8 hour to 24 hour window, I would suggest that you check with the specific battery manufacturer. Certain battery products may be able to recharge either faster or slower than the general rule allows.

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[JeanLuc]

Whilst Schaudt do not specify a maximum Ah battery bank capacity for the EBL, they do state the minimum charging periods to be observed before and after winter shut-down. They state a minimum of 12 hours for an 80 Ah battery and a minimum of 16 hours for 160 Ah. This suggests to me that they expected the EBL99/100/101 series to be connected to either one or two Exide 80 Ah gels as routinely fitted by German motorhome manufacturers in the early 2000s. The fact that there is no reference to banks of three batteries, coupled with the availability of an additional LAS121-2 charging module, indicates that it might be better to fit one if intending to run a battery bank of 270 Ah for example.

Concerning the inclusion of the starter battery in the battery bank size calculation, I do not see why this is necessary. Schaudt make no reference to it and it has certainly never been raised by Udo Lang in any exchanges that I have had with him. The EBL provides only a float charge of 2 amps (EBL 99/100) or 8 amps (EBL 101) to the starter battery and the habitation battery charging takes precedence over this anyway.

 

[maxi77]

that is the advice from Schaudt, and other charger manufacturers .

Ideally the Battery Bank size should be no more than 10 times the charger output. i.e. 18A x 10 = 180ah.

Schaudt aslo state the minimum for the EBL is 55ah.

the reasons are not because it would overheat the charger, it is about the optimal time to recharge the batteries.

Further reading with general rules..

http://www.tnbpowersolutions.com/sites/default/files/webfm/resources/upload/Industrial UPS/Battery Chargers/Application Paper/CYB_Proper Charger Sizing for Utility_APPLICATION PAPER.pdf

I agree the 10 times recommendation is generally to do with time to recharge, but in several places I have seen comments that Electroblocs are prone to fail if used to charge more that the 10 times the rated output.