Solar Panel topping up battery - which Diode?
Submitted: Saturday, Jul 30, 2005 at 17:11
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Alan Southport QLD
Hi there,
I know this more of a electronic thing, but i want to use a solar panel to constantly keep a charge going into a spare 12volt battery - so it's always going to be ok.
The solar panel only gives out 19volts @ 120ma but has no Diode in place. This means (I think), that at night the
battery power drains into the panel. So someone said i need a diode to allow the current in - but stop it going back out. But he didn't know what type to buy.
I was given some 1N4004 diodes, does anyone know if these will be ok. I don't want these little things melting if the battery is to 'powerfull'.
The battery is a normal SLA and it's rated power is 20amps.
Any help will lbe appreciated.
Thanks.
Alan.
Reply By: Member - Geoff M (Newcastle) - Saturday, Jul 30, 2005 at 20:59
Saturday, Jul 30, 2005 at 20:59
Alan,
A single 1N4004 in series with the panel and the battery will work fine.
Geoff.
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Follow Up By: V8troopie - Sunday, Jul 31, 2005 at 00:31
Sunday, Jul 31, 2005 at 00:31
Just for curiosities sake, turn your panel upside down on a flat surface, so that no light gets to the solar cells, and connect your battery via a multimeter set to Amps. You might have to set it to Milliamps.
I did that and was surprised how tiny the 'reverse current' actually is. Fat chance of not having a diode might be discharging the battery. The battery will lose more charge overnight due its own self discharge.
But don't take my word for it, try it yourself and possible save the hassle with the diode. Some panels might have more reverse current than the panels I measured.
Klaus
FollowupID:
378084
Follow Up By: BenSpoon - Monday, Aug 01, 2005 at 21:32
Monday, Aug 01, 2005 at 21:32
I've just spent the past few weeks trying to establish the cause of batteries going dead and dropping packets and phone calls in some of our solar powered microwave repeater stations. Added blocking diodes to each solar panel and the problems went away. dont underestimate the effect of a poofteenth of an amp being whittled away for hours on end whilst in shade and darkness!!
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Reply By: Member Eric - Sunday, Jul 31, 2005 at 08:08
Sunday, Jul 31, 2005 at 08:08
Silly question , do you have a regulator ? I know what happen's to a battery when you start pumping it with 19V , it explodes . 14.5 would be max in my books .
Regards EC
Ps . I have my solar panel ( through regulator ) plugged into my battery pack to keep it topped up . I have also have a HD 12 connector from the main battery connected in the rear . In case the altinator sh*ts its self , I can plug the connector to the panel as back up r to get me home
AnswerID:
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Reply By: Alan Southport QLD - Sunday, Jul 31, 2005 at 09:22
Sunday, Jul 31, 2005 at 09:22
Thank you for the replies from Gary and Eric.
Thanks Gary, that's all i need o know.
As for Eric, I appreciate your warning, but the solar panel is only 1.5W and gives out MAX 1.2ma. And so i thought that this 'really' would be a trickle charge and not enough to 'blow' the battery up.
And i considered that i would only be at peak power anyway for a few hours in the day.
The 19Vlt was when there was no load on it - sorry if i mislead you on that.
If you think that there is still a danger in that, could you let me know. With the low power i thought it would be ideal to just 'top' up the battery.
Thanks,
Alan.
AnswerID:
122967
Follow Up By: Member Eric - Sunday, Jul 31, 2005 at 10:21
Sunday, Jul 31, 2005 at 10:21
If its one of the trickle charge panels , desighned to plug straight onto the battery , it wont be a isue , I have seen them before , but dont know how effective they are .
I wouldnt waste my time with a diode
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Follow Up By: Member -Dodger - Sunday, Jul 31, 2005 at 14:25
Sunday, Jul 31, 2005 at 14:25
You should not need a blocking diode but if you want piece of mind a simple blocking diode at Dick Smith/Tandys will only set you back $1.50.
Place it in the positive wire then bobs your uncle.
Get one around 2amps.
FollowupID:
378119
Reply By: Alan Southport QLD - Sunday, Jul 31, 2005 at 18:27
Sunday, Jul 31, 2005 at 18:27
Thank you for all your replies,
I have place a 1N4004 diode in series on the POS line, and will see how it goes.
Interetsing that now when i start the vehicle and rev it, the Volt meter doesn't move higher as it used to. That must mean that the diode in place is now stopping the current from the vehicle, is no longer being registered.
So, it must be true that [booleen] the power from battery was being 'absorbed' by the solar panel at night. Therefore, it was in a constant state of charge and discharge! - Might have been ok in a state of 'hold' and then 'recharge'. But my case as it turns aout now was charge and discharge.
Which is why i had to get a new battery, after 10months! And why i decided to ask the 'experts' on this
forum, if it could be a 'drainage' - 'usage' issue, after getting a new battery.
So i will monitor it all and see how it goes.
My thanks again for the feedback and that's what forums are all about. It is truly amazing at how many people out there are very knowledgable and experienced - and they give it for free.
Thank you once again.
Alan.
AnswerID:
123028
Follow Up By: Member - Collyn R (WA) - Sunday, Jul 31, 2005 at 18:43
Sunday, Jul 31, 2005 at 18:43
Alan
The module in question should compensate for the internal losses of the battery. Whilst I am normally wary of advising the use of a solar module without a solar regulator this one should be fine. Just keep
water topped up.
Reverse diodes are primarily of use where solar modules may be covered for long periods (as is common with boats to protect against segullbleep). The diode introduces about 0.6 volt drop and in more typical use (such as yours) is likely to reduce the charge rate way beyond anything you may lose in reverse current flow.
Collyn Rivers
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