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I purchased the following solar security light kit a few weeks ago:

Harbor Freight #69643

Mounted system, worked great. FYI, the lamp uses a 6V, 900mAh, NiCd battery pack that is recharged with the included solar panel. I'm presuming that the controller is integral to the lamp assy, but I could be wrong (i.e. said controller may be integrated into the solar panel assy).

enter image description here

Well, we had a hail storm last week that totally destroyed the solar panel.

I have verified that it is NOT possible to purchase the solar panel separately, so I am considering the following scheme:

Purchase another security light kit - same model as the original purchase. I'd now have one solar panel assy and two lamp assy's. Next, I'd attach the two lamp assy's to the solar panel assy using a dc power splitter cord. Now, I'd have both lamp assy's wired in parallel.

My questions: Would this charge both batteries? I'm presuming that a larger recharging current would be routed to the battery with the lowest open circuit voltage. If the controller is mounted in the lamp, I'll have two controllers downstream of the cable split. If the controller is mounted in the solar panel component, I'll have one controller upstream of the cable split. Does it matter where the controller is mounted (see above)?

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    \$\begingroup\$ Can you dismantle the destroyed solar panel assembly to see what control/protection electronics are provided in that portion? \$\endgroup\$ – user2943160 Aug 7 '16 at 21:18
  • \$\begingroup\$ @user2943160, I will most likely do that and post my results. However, based on the YouTube video link provided by Passerby, below, I'm not expecting to find much there. \$\endgroup\$ – Digger Aug 8 '16 at 17:23
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    \$\begingroup\$ These lights wear out and break, so I have a handful of leftover solar panels. They are in the 9-11 volt range. Not really useful for anything else. \$\endgroup\$ – SDsolar May 23 '18 at 3:58
  • \$\begingroup\$ @SDsolar, I may be interested in purchasing one or more of said solar panels. The battery pack in one of my light units has given up the ghost, and I plan on installing a higher quality battery pack into same. At such time, I'm thinkin' it would be a good idea to mount another solar panel (I currently have two lights being charged by one panel, see the original post...). If you are interested, please contact me at careycher1@msn.com. \$\endgroup\$ – Digger Jun 16 '18 at 16:10
  • \$\begingroup\$ If you want to use multiple panels, or even multiple batteries, the bottom line is that they will all need to be in parallel. That way the Amps can add but the Volts will not. \$\endgroup\$ – SDsolar Jun 16 '18 at 19:42
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These things are the dumbest solar charge circuits possible. See a tear down here https://youtu.be/OSR2ofEAJKg

Solar cell to reverse protection diode to 6x series AA NiCD battery pack. No charge controller. It depends on the battery pack getting trickled charged, and being stronger than the solar panel.

Connecting the same panel to two lights will cut the current to both, and likely tripling the charge time (it won't be exactly half). The built in diodes on the input board will prevent one battery from charging the other, just as they prevent the battery from back feeding the solar panel in normal use. No modification or precautions needed.

These lights will already deep discharge the batteries over night as is, which is why NiCD are chosen. Their runtime will be reduced due to less power charging them.

FYI you can buy similar panels from overseas online for a few bucks. Probably from the same place HF gets theirs.

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  • \$\begingroup\$ Passerby, good find on that YouTube link! Based on the fact that the lamp unit see very light duty (because of where they are mounted), your assessment gives me the confidence that my charging plan will work well for my case. \$\endgroup\$ – Digger Aug 8 '16 at 17:23
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    \$\begingroup\$ I just purchased another Harbor Freight Solar Security Light kit (identical to the one featured in the original post). During the afternoon, I measured 11.8 volts of output from the solar panel. One would presume that, in early June through mid July, this solar panel could provide over 12 volts at solar noon. Seems to be plenty of margin - it should have no problem keeping two batteries charged, especially in light of the fact that the lamps see such light duty (see the above comment). \$\endgroup\$ – Digger Aug 10 '16 at 1:59
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In general, you can't because of the unknown function of the controller.

In the case of a solar cell, there is little damage except back current, which, changes are, the controller deals with.

Obviously when you connect two batteries you effectively double the load on the charger, but it doesn't matter do much because it can only supply what it can.

One problem in though is that it will not be able to charge up to the same voltage. This depends on the circumstances.

Second, Two batteries in parallel are generally not a good idea because one will try to charge the other. Of course, since these are rechargeable batteries this actually helps the case. At some point, if both batteries can be charged then their voltages will come to rest at some common value.

The down size is that this can be dangerous if one fails and the other tries to charge it up.

So, this is what to do:

  1. Charge both batteries, more make sure they have similar voltages.
  2. Measure the voltages of both batteries.
  3. Hook up one battery and the charger then measure the voltage. Do a spark test(touch wire charger wire quickly on and off of the batter and see how much it sparks).
  4. If all the voltages are similar hook up both batteries. First do a quick spark test just to make sure it the same as one and no excess power seems to drawn.
  5. Let charge somewhere safe for a little while... keep an eye on it. Check for excess power consumption(heat), etc...

If all this passes, and it should unless your controller or batteries are bad, then it should be rather safe.

Get two proper rated fuse and/or thermistors. (this would be probably about about 1-2x the current required by the lamp... slow blow) and wire them in.

Basically since the charger is just solar power and probably is very weak, changes of anything happening is pretty slim. There is probably not enough power there to do much of anything.

The batteries are the real issue, as they could explode(unlikely but possible) and catch something on fire. Note that you have more than 2x the same chance as with one battery.

The controller may not function with 2x load though as it might have some "intelligent" circuitry. The only way to know is to test or investigate more. You could add some slight resistance to the batteries to get the load back to what the controller would want. Your only wasting solar power anyways.

I doubt there is anything that could go wrong. If you do some quick light tests then chances are you'll be ok. Of course the controllers could be designed extremely poorly but even in that case I can't see how they would have a problem.

TLDR; The easiest thing to do is simply do some voltage measurements. Obviously the controller is meant to deal with "dead" batteries(within reason). If all the voltages look good then things should be good. It will take 2x as long to charge and there might not be enough daylight to make it effective but it should still "work".

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  • \$\begingroup\$ @Passerby You overestimate the usefulness of your comment. \$\endgroup\$ – AbstractDissonance Aug 8 '16 at 4:55

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