mppt charger

Thanks for that i think i will save myself the trouble and leave things as they are.

You would already be getting around the max for the regulator and two 300W panels in series wouldn't pass 30 amp through themselves. The max OC voltage would be near or more than 40volts. Will your regulator cater for that.

AS it is will work just fine and use the MPPT feature quite well.

That amount of panel for 2 x 120ah should see them fully charged most of the time with normal amp loadings.

If you are going to bung panels in series then first check what maximum input voltage your mppt controller can handle...

Ie Redarcs BCDC1225D max is 32v so would handle two panels but 3 might kill it
The Ctek D250s is about 22v

"Ie Redarcs BCDC1225D max is 32v so would handle two panels but 3 might kill it"

Malcom, two panels in series gives a Vp of around 44 V. That is far too high for a 32 V input.

Depends on the panels doesn't it. Not all panels put out 22v

Anyway, I'm sure the OP understood what I was alluding to.

I believe the 3210a tracer is rated at 100v pv input

Hi Tony,

I did some testing a while back with 100W panels, with 22V being feed to the panel its draw was very small ,it worked out that you would loose more across the series diodes than you would loose form the back flow into the panels.

I also tried it on my 80w flexible ones before adding the diodes.

When I had one in the shade and one in full sun, the current went up about 0.7A by disconnecting the shaded one. That's about 12w. I read that this heat is usually dissipated in one solar cell, the one with the lowest voltage in the panel. I didn't want to take the chance of blowing a solar panel while away.

Although the diodes introduce a loss, this can easily be compensated by a few dollars more on panels.

Each to their own, but every reasonably respectable solar site seems to advise it.

Maybe depends on the quality of the panel, can't see why one cell would dissipate all the heat as all cells in the string would have the same current flowing through them and similar voltage drops across them so they should all be dissipating similar power levels, even at 12W over say 36 cells that's 333mW per cell, can't see that doing any damage?

I would have thought if it was a big problem as the manufactures usually include bypass diodes they would also include blocking.

I have been using multiple panels in parallel for years without blocking diodes, if where camped under trees etc I put one out in the morning sun and position the others so they will pickup the sun as it moves through the day when where not there. Never had any issues or noticed any significant loss caused by the ones in the shade.