Solar panel charging 12V battery - prevent over charging

[David]

I'm trying to diagnose a possible problem with a solar panel on a motorhome.

The charge controller - NDS Energy Sun Control SC 15-240 - is supposed to charge the habitation battery, and then switch over to charging the vehicle battery.

This thing:

Manual (such as it is) at:

Now it seems to have charged the habitation battery, or at least is happy that the habitation battery is charged, because the LEDs show that it is only charging the vehicle battery.

Habitation battery is at 13.8V, vehicle battery is showing (through the Sargent EC450 controller) charging at about 0.2A with a voltage between

14.5V and 14.6V.

I think that the solar panel should no longer be charging the vehicle battery and that there may be a fault on the controller.

However the PDF manual gives 4 charging modes:

" A) Charge curve for ?GEL? battery B) Charge curve for ?FLOODED? battery C) Charge curve for ?AGM? battery D) Charge curve with limited voltage max 14.5V"

This makes me wonder if, where you have a different type of battery in the vehicle and the habitation, perhaps a Gel in the habitation and a standard lead/acid ?flooded? battery in the vehicle, if you need to use the voltage limited profile (D).

So is the solar controller behaving correctly?

If the solar controller is behaving correctly then there might be an interaction between the solar controller (happy to float up to 14.6V at low amperage) and the Sargent controller cutting out because an over charge has been detected.

Ah! Sun has just come out and 15.8V showing for the vehicle battery. Now that can't be right, Shirley?

Cheers

Dave R

[T i m]

Just OOI, where and with what are you reading these voltages?

I ask because if it's the display on the controller itself and it's on fairly long / thin leads between that and the batteries, it could be a metering thing or just a non calibrated meter etc?

I would be interested to see (if it's not what you have already done) is put a known / calibrated meter across the batteries themselves and see what they actually read in comparison to the controller display?

FWIW I have a fairly wide range of ages and chemistry of LA batteries here and I wouldn't like to set a specific voltage (down to two DP especially) on any of them! ;-)

Cheers, T i m

[Dave Plowman (News)]

Neither of those figures makes sense. A fully charged battery after left to settle for a while doesn't read anything like 13.8v That is the figure you'd see when on a float charge.

And a ordinary car battery with 14.5v across it will take a lot more than

0.2amp.

You need to measure the actual battery voltages with a decent DVM.

[David]

Solar panel goes to solar charge controller then via a short lead to the main charge controller which handles all the motor home electrics, 12V and

240V.

The voltage is on a digital read out on the main charge controller so I assume that it is accurately measuring the incoming voltage from the solar charge controller.

I've seen it go as high as 15.8 V which is higher than the supposed maximum output of 14.5 V, so I've disconnected the solar input because it seemed to be tripping the safety settings on the main charge controller.

Now working O.K. as far as I can tell.

The whole thing confused by the fact that the 30A fuse to the habitation battery had blown so some symptoms were due to that.

Cheers

Dave R

[Cursitor Doom]

I just use a 14V zener diode across the battery to cap the solar panel's output. You don't need anything fancy or complicated for a simple application like this.