Battery Master and solar panel

I am thinking of adding a solar panel on the roof of my 1996 symphony to charge my leisure battery and then fitting a battery master to keep the van battery charged as well. I understand that the battery master will only allow the current one way, what bothers me is, will it interfere with the alternator which also charges both batteries.

I have same setup on Nuevo with no problems for 3 years now. Best thing we've done, not had a flat battery since.

Paulmold wrote:I have same setup on Nuevo with no problems for 3 years now. Best thing we've done, not had a flat battery since.

Me too for two years, and on the previous van for four years.

100% agreement with Paul and Al.

Same here, worked a treat on my last vehicle.

However, even better..... it is possible to get solar panel controllers that can split the charge between the batteries. I have one on my current van. By default it was set to send most charge to the leisure battery (80 or 90% from memory) but it can be switched to 50/50, which I have it on whilst parked on the drive. One less potential source of a fault and saves the cost of a separate device.

matchlessman wrote:However, even better..... it is possible to get solar panel controllers that can split the charge between the batteries. I have one on my current van. By default it was set to send most charge to the leisure battery (80 or 90% from memory) but it can be switched to 50/50, which I have it on whilst parked on the drive. One less potential source of a fault and saves the cost of a separate device.

Up until quite recently, all of the Sargent controllers with built-in solar regulator had this type installed.

It's different, but it's not better in every circumstance. The ability to select the ratio is good (though on the Sargent it's not so easy to do as supplied from the factory), but the downside is that, because the controller effectively switches solar output between batteries on a "time slice" basis, if a battery is already fully charged, its proportion of the solar panel output is effectively wasted.

The Battery Master can make use of excess charge on one battery by effectively allowing it to "overflow" to the other. But, until the first battery approaches full charge, the second battery will get nothing. So... different but not necessarily better...

-mojo- wrote:

The Battery Master can make use of excess charge on one battery by effectively allowing it to "overflow" to the other. But, until the first battery approaches full charge, the second battery will get nothing. So... different but not necessarily better...

Is that strictly true Mojo?

Far be it from such an electronics numpty as me to challenge you, but I understood it to work on the differential between the two batteries of a couple of volts or so. If the vehicle battery was (say) two or more volts lower than the habitation battery, power was taken from the hab to the vehicle battery, whether or not the former was near fully charged.

I could be wrong of course - it has happened!  

Gromit wrote:

-mojo- wrote:

The Battery Master can make use of excess charge on one battery by effectively allowing it to "overflow" to the other. But, until the first battery approaches full charge, the second battery will get nothing. So... different but not necessarily better...

Is that strictly true Mojo?

Far be it from such an electronics numpty as me to challenge you, but I understood it to work on the differential between the two batteries of a couple of volts or so. If the vehicle battery was (say) two or more volts lower than the habitation battery, power was taken from the hab to the vehicle battery, whether or not the former was near fully charged.

I could be wrong of course - it has happened!  

No. you're right. What I said was too much of a simplification. What actually happens will depend on the state of charge of both batteries, plus a number of other factors such as the exact way in which the cabling has been done.

The example I gave is if the leisure battery is significantly depleted. Under those circumstances it's likely that the solar panel won't lift its voltage high enough above the vehicle battery voltage for any charging of the vehicle battery to happen.

When the charge state of the leisure battery rises enough for its terminal voltage to go above the "trigger" voltage difference for the Battery Master, some charging current may start to flow to the vehicle battery, but the bulk of the panel's charge will still go to the leisure battery.

[Edit: I should add that a "typical" Battery Master install almost certainly places the leisure battery at an advantage compared to the vehicle battery. That's because typically the solar panel connects directly to the leisure battery via relatively large cables (6mm2 in my case). The cable from the Battery Master on to the vehicle battery is typically longer and relatively light gauge, so there will be a significant voltage drop along its length when charging current is flowing. This alone will favour charging of the leisure battery.]

Thanks Mojo.

I'm quite chuffed at being right - even if I don't fully understand why I am! 

To quote a well known DJ "Wise words mate" 

Gromit wrote:Thanks Mojo.

I'm quite chuffed at being right - even if I don't fully understand why I am!