Monday, Mar 16, 2009 at 11:54
G'day Mainey,
I read your profile and details of your setup. I was wondering why you dont leave the Steca set-up permanently with some sort of shunt to measure the charge from the vehicle while travelling?
I know you state that the Steca is only used once you are camping but surely the SOC it gives, if based purely on the voltage of the batteries, cannot be considered to be very accurate? The only info the Steca would have is the charge in, out and battery voltage from when it is connected. It has no prior knowledge of the battery condition.
When I had the
Kimberley Kamper I used a PL-20, 15A Projecta 3-stage charger, 2 x 123W Sharp panels, 305 AH of AGM batteries and a shunt. When the Kamper was not in use, the charge coming in via the Projector charger was measured by the shunt and taken into account by the PL-20.
Once the panels were in use, it also measured the same things that you do, but instead it still had the overall view of the battery state in its memory.
I've followed the same principle with the caravan, with the only difference being that I have 520Watts of panels and 480 AH battery capacity with a PL-60 and a 60 Amp battery charger. The principle remains the same, just the sizes are different.
When I worked in Communications we had several Solar installations using wet cells. It was pretty obvious that battery voltage alone, when used to estimate State of Charge, was horribly innacurate. This was easily confirmed by testing with a hydrometer.
So if we are using the SOC as an "electronic hydrometer" (as you can't really test sealed cells any other way), then ALL of the current going into and out of the cells needs to be accounted for for accurate readings.
I don't know anything about the Steca units. Can shunts be fitted to them?
Cheers
Russ.
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