Using Solar Panels of different voltages?

Question:

To the best of my knowledge, all the panels you mention have diodes to prevent reverse current flow. So, no current from your higher-voltage panel will flow backward through the M55. If you connect the M55 in parallel with the new panels, you should get additional current from it in bright sun; in low sun conditions it will not affect anything. Solar panels are run in current mode, not voltage mode, by most controllers, but of course the voltage of the panel must exceed the battery voltage plus the controller drop. Do make sure, however, that the controller will handle to max current of the combination. I’d want to run an experiment with metering etc. before I could offer advice on hooking each panel to a separate controller then paralleling the controllers. The result will depend on the precise control function of each controller and how they interact. With quality controller design, this *should* work.

Response:

Thanks to Warren, Andy and John for your quick responses! I’ll give a try installing both panels in parallel through the charge controller.  Yes, John, both panels _do_ have built in isolation diodes, so I shouldn’t have any problems in that regard. I’m a ham, so your explanation, Andy, makes sense to me. Warren, the batteries are brand new.  I bought the rig used last week, and the dealer replaced _all six!_ (2 starting, 4 house) batteries with no prompting by me! And it wasn’t even part of the deal! When they did the pre-delivery inspection, they discovered marginal batteries and replaced them all. (GOOD DEALER! – Lazy Days RV near Tampa. Can’t say enough for their customer oriented attitude, but that’s another story.) So hopefully, I can modify the solar charging system before there is some damage. I expect the only problem I’ll run into is finding and isolating the existing wire running from the solar panel to the battery, so I can install the controller. I assume the manufacturer had the common sense to run it through a fuse, so the first spot I’ll check is the 30 or 40 fuses scattered all over the place. :-) Wish me luck! Gary  WB0BZR My ‘new’ ’94 Safari motorhome has a Siemens M65 solar panel factory installed, charging 4 – 12 volt deep discharge house batteries in parallel.  These batteries are new, and were installed by the dealer when I bought the rig. They look like group 27 batteries. I have a Siemens M55 panel I’d like to also install on the rig, but I don’t know if I can, because these panels produce different output voltages. The M55 is rated at 21.7 volts open circuit, and the M65 is rated at 18.0 volts.

—-SNIP—- — Gary Sanders Bait for spammers (With credit to E. Needham):

Response:

My ‘new’ ’94 Safari motorhome has a Siemens M65 solar panel factory installed, charging 4 – 12 volt deep discharge house batteries in parallel.  These batteries are new, and were installed by the dealer when I bought the rig. They look like group 27 batteries. I have a Siemens M55 panel I’d like to also install on the rig, but I don’t know if I can, because these panels produce different output voltages. The M55 is rated at 21.7 volts open circuit, and the M65 is rated at 18.0 volts. The existing panel (M65) is installed without a controller, and I noticed in the installation literature that it’s possible to overcharge the battery when no controller is used. I have a controller (SCI Mark 3/15) with the M55 panel. If the two panels can be used together, would it be a good idea to connect both of them through the controller?  And can the two panels be used together? Anyone have any ideas? Gary — Gary Sanders Bait for spammers (With credit to E. Needham):

Response:

  Several questions here – see comments below….. — Electricity from the sun http://www.windsun.com

:My ‘new’ ’94 Safari motorhome has a Siemens M65 :solar panel factory installed, charging 4 – 12 volt :deep discharge house batteries in parallel.  These :batteries are new, and were installed by the dealer when :I bought the rig. They look like group 27 batteries. : :I have a Siemens M55 panel I’d like to also install :o n the rig, but I don’t know if I can, because these :panels produce different output voltages. The M55 is rated :at 21.7 volts open circuit, and the M65 is rated at 18.0 :volts.   Yes, you can use panels with different voltages.  What will happen is that at a certain point of either/or high temperatures or high battery voltage, the M65 will simply not have enough voltage to do anything.  It will essentially just drop out of the circuit or provide very little. : :The existing panel (M65) is installed without a controller, :and I noticed in the installation literature that it’s :possible to overcharge the battery when no controller is used. :I have a controller (SCI Mark 3/15) with the M55 panel. :If the two panels can be used together, would it be a good :idea to connect both of them through the controller?  And :can the two panels be used together? :   Yes – just wire them in parallel and run them both through the controller. If you have been running it straight into your batteries for a while, there is probably already some damage done, especially if you have spent much time in cool or cold clear weather.   The M65 (now called SM46) is one of the so-called "self regulating" panels.  What they actually are is low voltage, 30-cell panels.  Problem with them is that they actually only put out the ideal voltage at about room temp – lower temps, they put out too much, higher not enough.   The SCI 3/15 is not my favorite controller, but if you have it, use it.

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