Bfg Posted October 4, 2016 Share Posted October 4, 2016 Put a diode inline with the solar panel and you'll drop 0.7v across it making it easier on the battery A 1n5401 will do the trick, they're pence off ebay. Put it in the Positive lead with the stripe towards the battery.That's great thanks. I'll do a check tomorrow (if it's bright and sunny) and see what the voltage reading peaks at. Would covering part of it with taped-on card or perhaps a mesh not do the same ? ..as this type of panel doesn't stop working altogether even when part of it is in the shade. When I was looking before it would drop below 14v every time a cloud came across, even though it was a bright day. And then drop below 12v when a darker cloud deemed to visit our air space. Link to comment Share on other sites More sharing options...
cobblers Posted October 4, 2016 Share Posted October 4, 2016 You could just cover a bit of it but it's hard to work out how much you can cover and have it still actually provide some charge etc.In practice (and this weather) it's unlikely to push a proper car battery with any kind of parasitic load still on it way up to 15V, but sticking a 20p diode inline will make sure it doesn't. Link to comment Share on other sites More sharing options...
overrun Posted October 4, 2016 Share Posted October 4, 2016 My Astra ruined a brand new Bosch battery over last winter, totally drained in 6 months and wouldn't even take a sniff of charge. It's fine when in use though.Hope you returned it under warranty! I have two Aldi CTEK copy chargers. One is great and has seen loads of use.The other didn't even know it was a charger from day one and just flickered the power light. That one will be returned when they get some more in. Link to comment Share on other sites More sharing options...
PhilA Posted October 5, 2016 Share Posted October 5, 2016 That's 24V on the solar jobbie with no load. Vspec is 15V, and at the rated current. That's good for a 12V battery. Solar panels really bog down in voltage when across a load. The 15W panels I have produce about 23V into my vacuum tube meter in bright sunshine. Phil Link to comment Share on other sites More sharing options...
michael1703 Posted October 5, 2016 Share Posted October 5, 2016 Not many cigarette lighter sockets are permanently live, so you'd be better with crocodile clips on the battery Link to comment Share on other sites More sharing options...
michael1703 Posted October 5, 2016 Share Posted October 5, 2016 This is the sort of thing I was thinking of getting http://www.ebay.co.uk/itm/1-5W-SOLAR-PANEL-12-VOLT-BATTERY-SAVER-TRICKLE-CHARGER-BOAT-CARAVAN-CLASSIC-CAR-/232095210518?hash=item3609f3dc16:g:UMcAAOxy4fVS-4hO Link to comment Share on other sites More sharing options...
cobblers Posted October 5, 2016 Share Posted October 5, 2016 That's 24V on the solar jobbie with no load. Vspec is 15V, and at the rated current. That's good for a 12V battery. Solar panels really bog down in voltage when across a load. The 15W panels I have produce about 23V into my vacuum tube meter in bright sunshine. Phil Oh aye, I didn't see the pic. Looks like it's just totally unregulated so the diode won't do much, it's just relying on the battery being big enough to handle it, and tbh it'll probably be fine. Don't worry about it. Link to comment Share on other sites More sharing options...
Bfg Posted October 5, 2016 Share Posted October 5, 2016 Must put my hand up to say I have very little idea what Vspec means &/or why the label should tell me 24v volts when that appears to be 'when not connected' to a battery ie., totally irrelevant ? I'm capable of learning but just haven't studied the subject at all. And so until I do.., are you both agreeing that (pending an unknown fault in this panel) it will, unaltered ..sitting on the dashboard of my Voyager, keep its battery nicely charged for the weeks I am away. Without bursting into flames and in doing so destroying every other car in the airport ! .... Link to comment Share on other sites More sharing options...
PhilA Posted October 6, 2016 Share Posted October 6, 2016 I guess you can think of it in terms of mechanical stuff. Think of the panel like a small 2-stroke engine. How much sun shines on the panel is how wide you open the throttle. How fast the engine turns is the voltage. How much torque it makes is the current (Amps). Say the engine is on a small motorbike. To get up a steep hill you need wide open throttle but under load the engine only has enough torque to run at half speed. However, pull the clutch lever and the engine screams up to maximum. Similar concept, the panel can't supply maximum current and voltage at the same time so when it's not connected to a load it isn't regulated and makes a high(ish) voltage. Across a fairly well charged battery the amount of voltage it makes drops as the amps flow. If you short circuit it, the volts drop to zero, same as if you stall the engine by loading it too heavily (stamp on the brakes and require more torque to turn than the engine can make). Kinda like that, anyway. Phil Bfg 1 Link to comment Share on other sites More sharing options...
drum Posted October 6, 2016 Share Posted October 6, 2016 I bought a cheap solar trickle charger from machine mart yesterday.Testing it with the multimeter gives a reading of about 22 volts with a watery October sun. Is there a way of testing the current? I tried attaching the charger to a battery and measuring the current inline on the negative side but didn't get a reading. Link to comment Share on other sites More sharing options...
PhilA Posted October 6, 2016 Share Posted October 6, 2016 If your multimeter has a mA setting you should be able to hook battery to meter, meter to panel, panel to battery. Look carefully, my meter has a different socket with a shunt that you need to plug the red lead into for it to read current. Phil Link to comment Share on other sites More sharing options...
PhilA Posted October 6, 2016 Share Posted October 6, 2016 Is that right?I thought load was the same as resistance and a short circuit would be zero load?But 'lectrickery has always been a mystery to me.BenZero resistance, full load. The more resistance you have, the less current is able to pass, the less load you have on the device. Disconnect it and the air between the connectors is a very good insulator and has a very very high resistance so no current flows, no load. Phil Link to comment Share on other sites More sharing options...
They_all_do_that_sir Posted October 8, 2016 Share Posted October 8, 2016 ​lidl are doing cheap ones over here atm sub £20 if I remember Link to comment Share on other sites More sharing options...
purplebargeken Posted October 8, 2016 Share Posted October 8, 2016 I have about 3 of the things. I'll grab a random one and lob it in the post for you. Link to comment Share on other sites More sharing options...
drum Posted October 8, 2016 Share Posted October 8, 2016 If your multimeter has a mA setting you should be able to hook battery to meter, meter to panel, panel to battery. Look carefully, my meter has a different socket with a shunt that you need to plug the red lead into for it to read current. PhilYep, that's what I did but didn't get a reading. Will there need to be current being drawn by something in order to get a reading, so nothing when just being charged? Link to comment Share on other sites More sharing options...
PhilA Posted October 8, 2016 Share Posted October 8, 2016 The battery you hooked it to probably had a higher voltage than what the panel was able to push out, so the diode inside the panel stopped the current flowing backwards (without, at night the battery would just make the panel get warm and flatten the battery). Truth, the UK isn't sunny enough for shite solar panels drum 1 Link to comment Share on other sites More sharing options...
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