#141900  by plainsnailing
 Tue Jun 19, 2018 7:57 pm
What's up ? (Trying to charge 24V start from solar. using AliExpress bits)
After reading this discussion, fitted circuit board, oops only regulated power supply.
Changed to charger circuit board but pots would not adjust.
Changed to charger circuit board with digital display, can set V & A and it works.
BUT - have MCB between solar panels and Votronic MPP250 controller.
Feed to charger is from controller side of MCB.
With MCB open 12V house batteries are charging 24V start batteries thru charger ??
To quote from Votronic manual "Standard protection against overload, overheating, reverse battery and back discharge of the battery (in case of insufficient solar power, such as at twilight, at night etc.)."
Charger won't run on power from 24V.. requires input power.
I guess I need blocking diode from MPP250 ? What size?
 #141903  by Neddy
 Tue Jun 19, 2018 9:11 pm
"Feed to charger is from controller side of MCB.
With MCB open 12V house batteries are charging 24V start batteries thru charger ???"

No, they're not. With the MCB open, the charger device gets no power from the solar panels and thus cannot provide any charging output for the Starter battery.

Because the solar controller has "Standard protection against reverse battery and back discharge of the battery", no current can flow from the 12v House batteries to the charger device - regardless of whether the MCB is open or shut. You don't want it to, of course. Why deplete your House battery just to Float charge your Starter battery? Much better to float it directly from the solar panels, using power that might otherwise go to waste.

 #141929  by plainsnailing
 Wed Jun 20, 2018 6:59 pm
I agree with the theory, but what IS happening is what I described.
With solar disconnected 12.8V is showing at Solar + bare terminal.
With cable attached from solar + , charger is happy to output 27V (set) @ about 2A (set for 1A :roll: ) to start batteries. Blocking diode between solar + and charger input (fitted correct way around).
MPP250 otherwise works as expected, so either internal fault or Manual includes the now popular "alternate truth".
I have AliExpress "Blocking Diode 15amp 45V High Surge Current Capability 15SQ045 High Quality For DIY Solar Cells Panel". Any problem using one to stop reverse current ? Solar is 2 x 150W seried.
 #141941  by Neddy
 Wed Jun 20, 2018 9:34 pm
It would appear that the solar controller is failing to prevent "backflow" of current from the House battery to the solar panels. It should, but installation of a blocking diode between the solar panels and the controller would stop this happening. The diode you mention would do the job OK. It will be working fairly close to its rated maximum voltage, but well within its current rating.

 #141948  by Neddy
 Thu Jun 21, 2018 10:00 am
I think the 15amp 45V diode you have already got would be adequate, but you could go for one with slightly higher current and voltage specs. If you want to minimise voltage drop, use a Schottky diode.

 #145093  by MiriamNZ
 Fri Oct 05, 2018 3:01 pm
After the stressfull installation in May, where the sparky didnt like the idea of using solar so used my house battery instead, (which has been disabled these last 4 months), today i got another sparky to finish the job.

I have 2 solar controllers, and its connected to the one with the 190W array.

The sparky has joined the new cable along with the wire bringing power in from the solar panel. So those two wires are poked into the input hole of the controller.

This new wire then runs to the device, and the device sends power to the truck battery.

His concern was that the volts from the solar panel are variable, this morning 20v. I loaded the device specs which say it can take variable voltage up to 30v.

The previous sparky put a (5v i think) fuse between device and truck batteries. That is still there.
There is also an identical fuse between the connection to the solar controller/panel join and the device.

The thing is set to float the calcium truck batteries at 27.6v .

The truck battery was sitting at 27v after a 15 minute drive this morning.

Does this all sound right and good?
Not certain i have the diode thingy to stop back flow.
Is that 27.6v an ok voltage?
Thanks for your help.

Cheers Miriam
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