Solar Panel Blocking Diode not Working?

[Duncan]

I recently started using a very small "battery maintainer" solar panel (1.8W, 125 Ma). The user's manual claims that it has a blocking diode, but I am seeing more voltage loss in the battery it is connected to than in the other battery.

The solar panel is plugged to the 12V socket ("cigarette lighter" type), and the battery switch left on to "1". The socket is on its own circuit, so this is switched to "on" at the electrical panel (but nothing else). Everything runs through the panel except for the engine starting circuit, i.e. nothing is hooked up straight to the batteries.

I think this means that battery #1 is either discharging through the solar panel, or somewhere else in the open circuit. I am thinking of testing this by doing some re-charging, then clipping the solar panel leads straight to the battery. I'll leave the battery switch to "Off".

Does this make sense? Could the blocking diode be dysfunctional?

[Maine Sail]

Your phantom loads, stereo memory, LPG sniffer, bilge pump etc. etc. could be more than what the solar panel can even keep up with let alone charge. In hot weather that panel will hardly keep up with the self discharge let alone put any charge into the bank..

Does the panel have a charge controller? Do you have an Echo Charger or ACR? Bilge Pump? Is the panel shaded? Count on about 5 hours per day at max current for the panel which will be under 0.625 Ah, on a good day. 0.625 Ah/day is barely a maintainer for a small battery let alone a bank of any decent size.

Also when you say "voltage" how did you get that bank up to charge before using the solar panel to maintain it. If this is a house bank and you're comparing it to a mostly unused starting bank then the solar panel won't do much to bring your SOC up on the house bank at all, it's just too small. It may maintain its SOC position and it also may not especially if you have a bilge pump that kicks on occasionally.

[Duncan]

Thanks, guys, for your replies.

1) As I tried to express, there should be nothing drawing current. I figure, since the voltage is dropping, there is either a fault in the circuitry, or the panel is discharging the battery.

2) I know the panel's output is tiny: it's inexpensive and experimental. My goal was just to mitigate the self-discharge rate of the batteries, which it should be able to help with, anyway.

So, I think I will proceed with the idea of clipping the solar panel leads straight onto the battery, just as a test. That way, I can leave the battery switch off.

If the battery still loses significant voltage, then I'll know it's the solar panel. If not, I'll know there is something screwy in the boat's wiring.

Thanks again

[Carl-A259]

Don't discount that the battery is simply drawing down on it's own. For your test to be conclusive, let the battery set with nothing hooked to it.

[Duncan]

Don't discount that the battery is simply drawing down on it's own. For your test to be conclusive, let the battery set with nothing hooked to it.

Thanks, Carl.Your point about the battery fading on its own is a good one. Maybe it just won't hold a charge.

I did a little test last night, by charging them both up. Then I used the one that had been down a lot when hooked up to the solar panel. Mostly, I only had one cabin light on, for about three hours. Even so, it was too run down to turn the starter over this morning.

So, it could be that that this battery is used up, while the other (identical) one is still good.

[Carl-A259]

Duncan, This isn't your problem but,,,(and you may already know this) As a quick note don't leave batteries connected together, it seems that one will draw down some ,then the other draws down some and as the batteries try to even out they just keep pulling each other down till dead. If your near just about any auto parts store, they will load test a battery for free. Their hope is you'll buy a replacement from them, at some point.