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Dinosaur

Guru

Joined: 12/08/2011
Location: Australia
Posts: 311

Posted: 09:04am 10 Nov 2011

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Hi All

To refresh,a solar system for the caravan.

If I am spending a lot of money on an MPPT solar charger,
it seems to make sense to me, that the MPPT should be the only one in charge of controlling the Battery.
So, if I am on the 240v grid, and my battery needs boosting, then instead of
using another battery charger, can I use an off the shelf power supply that has
say 30vdc @ 15 Amps.(for 24 vdc PV's) Then with a protection diode connect that to the MPPT input.

Typically this would happen at night time, when the PV's are not active.Could also happen when free camping and the generator is on for whatever reason.(Washing Machine etc)
If both the PV's and the power supply have protection diodes and common ground, then electrically I can't see why not.
What ripple range would be considered a problem.?

Regards

Regards
Hervey Bay Qld.

Dinosaur

Guru

Joined: 12/08/2011
Location: Australia
Posts: 311

Posted: 09:15am 16 Nov 2011

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Hi All

WOW, no reply for a whole six days.
Have I wet the bed here, or is there no obvious answer.

RegardsEdited by Dinosaur 2011-11-17

Regards
Hervey Bay Qld.

Tinker

Guru

Joined: 07/11/2007
Location: Australia
Posts: 1904

Posted: 02:56pm 16 Nov 2011

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Well, I read your question but choose not to answer because I have not tried that so no practical experience.
I do not know how exactly a MPPT unit treats incoming power.
However, I do know that one can safely short circuit a solar panel but that may not be a good idea with a DC power supply. It may or may not be relevant.

Some observations from my solar system: The open circuit panel voltage is about 44V, that is seen on the meter when the battery bank is full. When the battery bank accepts all the charge the panels can provide the panel voltage drops to around 35V.

Its your expensive MPPT unit, so why not try it out and report here how it went

Klaus

64bit
Newbie

Joined: 21/11/2011
Location: Australia
Posts: 2

Posted: 09:33am 23 Nov 2011

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Cost of the electronics and expertise needed would be cheaper to buy a battery charger.

Dinosaur

Guru

Joined: 12/08/2011
Location: Australia
Posts: 311

Posted: 08:49pm 23 Nov 2011

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Hi All

I have the expertise needed, and the components to put this in affect are very few.
1. Off the shelf PS (heapes cheaper then a charger)
2. Two 100A SSR's (to switch one DC supply in , and the other out)
mOhm ON resistance, and 3 to 32 vdc control.
3. One DPST Toggle switch.

Then the power can come via grid, generator or solar panels.

If I get a separate Charger, I am still going to have to protect the
Solar Charger from the Battery charger with isolation SSR, so I still think
the overall cost is lower this way.

Regards

Regards
Hervey Bay Qld.

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