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7watt solar panel as trickle charger?


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#11 roverjohn

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Posted 31 May 2019 - 07:59 PM

Vic,

I would never feed the battery directly because I'd have no idea how long you could do it safely. I just looked online and found some 3A pwm solar charge controllers for $4/ea. I'm sure I can find the modules for a buck or something but I'm not sure it's worth the time. I'll order a couple tonight just to satisfy my own curiosity. Like the OP I have a few 5-7 watt panels sitting around.

I'll post a link once I find out if I've wasted my $8.


Edited by roverjohn, 31 May 2019 - 08:01 PM.

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#12 roverjohn

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Posted 31 May 2019 - 08:06 PM

Vic,

I missed your 2nd question. Your truck is never going to see 17 volts unless you boil the battery dry.  We're talking about 1/3A charging current here so even the slightest load will pull the voltage down if you left the batteries connected which I would not do.


Edited by roverjohn, 31 May 2019 - 08:12 PM.

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#13 hpcbmw

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Posted 01 June 2019 - 03:45 PM

Thanks for all the input. I'm thinking that the 7w is pretty much useless for the truck and camper. I'll probably get a cheapo charge controller like Roverjohn suggested and use the 7w as a battery tender for my motorcycle/quad batteries.

 

Using the math above, it seems like the 15 Harbor Freight panel is still probably not enough to maintain all three batteries- but I've got three of the 15w panels. How about if I hook up one 15w panel to the truck batteries and one 15w panel to the camper? I'll run both through a cheapo charge controller.

 

Roverjohn- what website did you find the $4 charge controllers? I did a quick search and couldn't find them for under $7.50 on amazon, and not much cheaper on Banggood.

 

Quick question about charge controllers: I've got an older charge controller that came with a 100w panel I got used (it came with the camper). I had a problem one weekend with the batteries seeming to lose charge overnight. Is there a way to check and see if the charge controller is drawing power FROM the batteries when the sun goes down? It could be that the batteries were old at the time, I've since replaced them, but now I'm afraid to use that controller for fear of damaging my new batteries. 

Thanks for the help!


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#14 ntsqd

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Posted 02 June 2019 - 04:29 PM

This company has been selling these kits for a very long time:

 

https://www.pulsetec...r-chargers.html

 

Yeah, you could probably build something like it for less. How much is your time worth?


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Thom

Where does that road go?

#15 Happyjax

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Posted 02 June 2019 - 05:58 PM

Buy a 50 watt panel and a cheap solar controller and you can do lots with it for about $100


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#16 FoxenTec

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Posted 03 June 2019 - 03:08 AM

Related to this discussion.  I noticed when I was testing with a 5 watt solar panel from Zamp and a medium sized motorcycle battery, that the solar panel would bring up the battery during full sunlight to about 12.9 volts but as soon as the sun went down, I could see the voltage dropping on the battery.  

 

Was the solar panel because of no controller actually drawing energy away from the battery during these "no sunlight" hours?  

 

Sorry, still trying to learn.


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Jon

 

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#17 ntsqd

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Posted 03 June 2019 - 12:37 PM

Usually there's a diode function in solar panels, so I doubt that's what you were seeing. More likely is that the battery was achieving it's resting voltage. Can't measure a lead-acid battery's voltage immediately after the charging source is turned off. Need to let it rest for a while before such a measurement is valid.


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Thom

Where does that road go?

#18 roverjohn

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Posted 03 June 2019 - 12:50 PM

HPCBMW,

The charge controllers I found were on ebay. Just search '3w solar charge controller'.


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#19 Old Crow

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Posted 03 June 2019 - 01:16 PM

Related to this discussion.  I noticed when I was testing with a 5 watt solar panel from Zamp and a medium sized motorcycle battery, that the solar panel would bring up the battery during full sunlight to about 12.9 volts but as soon as the sun went down, I could see the voltage dropping on the battery.  

 

Was the solar panel because of no controller actually drawing energy away from the battery during these "no sunlight" hours?  

 

Sorry, still trying to learn.

 

You may just be seeing normal activity.  In general, a fully-charged battery has a 'resting' or 'no-load' voltage of something like 12.6 or 12.7 volts.  The solar panel applies a higher voltage (when the sun is shining) to counter-act the battery's tendency to self-discharge.  When the sun goes down it can no longer apply that voltage and the battery's voltage will drop back to its resting voltage.

 

You can see this same thing in your car's charging system.  If you measure battery voltage after the car sits overnight, you'll see its resting voltage.  Measure again with the car running and you'll typically see voltage in the 13s or 14s.  That's the alternator applying a charging voltage. Once you turn off the car, the battery's voltage will go back down to its resting voltage.

 

I used the word 'may' to start this post because we don't quite know enough about your Zamp maintainer setup.  According to this Zamp maintainer page, those panels are supposed to be paired with a controller.  In some cases, manufacturer's put what are called 'blocking diodes' in panels to prevent the very problem you're asking about and those panels wouldn't drain the battery.  But Zamp may not do that, particularly in their panels specifically designed to include a controller.  If that's the case, it would indeed drain the battery.

 

.

PS- I see ntsqd's reply came in while I was writing this up but I decided to post my wordier version anyway. :)


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