#140642  by rawill
 Thu May 17, 2018 10:39 am
Some say that I can be a bit "bloody minded!"

I could not possibly comment, except to say, "I like to win!"
Be it motor racing, or anything else!
 #140662  by plainsnailing
 Thu May 17, 2018 7:33 pm
OK sleuths, my solar is 2 x 85W in series thru MCB to Votronic controller, nominal 34.4V, actual 38 - 41V at controller. I then fitted power supply same as Robin to trickle charge 24V start batteries.
PS input connected from controller side of MCB thru blocking diode to PS input, 0V back to controller 0V.
PS output (set 27.0 to 27.3) thru fuse to 12V bus, 0V to 0V bus.
With PS connected to solar, current at MCB / PS drops to about 26.5V and PS output 24.2 rising slowly to 25.9 (battery not yet fully charged) and current varying (bad weather) from high of 1.0 to low of 0.1A.
If I pull the fuse (no output from PS) voltage at MCB pops back up to 38V or thereabouts.
No diode in PS output, it needs power from battery to operate.
I would expect current to be shared but voltage remain relatively constant :?: :?:
 #140674  by Neddy
 Thu May 17, 2018 9:32 pm
An MPPT Solar Controller is always striving to find the optimum voltage to run the solar panels at. When circumstances change (more sun, less sun, something else sharing the solar panel output) the controller will adjust the panel voltage to best suit the new circumstances. This is all as it should be and varying solar panel working voltages are only to be expected. Similarly, widely varying current flow to the 24v battery must be expected. If you feel that the 24v battery is getting too big a share of the solar panel output, all you have to do is reduce the 24v charge current a bit.

"PS output (set 27.0 to 27.3) thru fuse to 12V bus"
This is a typo - right?

 #140735  by MiriamNZ
 Sat May 19, 2018 9:26 am
I’ve got the first device suggested installed. The man told me what voltage he set but i wasnt paying attention. Hes coming back on Monday.
I think the device should be set at 27.4 volts.
Is that right?

I can get it adjusted on Monday if need be.
Second question, how is that number arrived at?

Cheers Miriam
 #140736  by Neddy
 Sat May 19, 2018 9:36 am
The device should be set to the Float voltage recommended by the battery manufacturer.

This is quite likely to be 27.4 volts.


Miriam, do you have a digital multimeter?
If not, could I talk you into getting one?
I sense that you have DIY potential!
 #140745  by MiriamNZ
 Sat May 19, 2018 11:13 am
I DO own a digital multimeter, inherited from my Dad. I even know where it is. I might have used it once or twice. I think id like to learn. (Own, even, might, think ... a lot of diffidence here). I read and read on power and i understand it for an hour or two then phhtt its gone and i have to read up again. :D

To get the voltage number, i guess i read the specs off the side of the battery and look up the manufacturer? :D

I really like to KNOW. Enjoy the research. Just come from reading that long article on lithium batteries (https://marinehowto.com/lifepo4-batteries-on-boats/). Dont understand the detail but still interested to read and take in what i can.

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