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Mppt want's 1.5X battery voltage to run properly?

PostPosted: Sat Sep 22, 2018 10:08 pm
by Jman
Hello all.

I was told this as a general rule and wanted to know how much of it is true?

With a 12v system, will a standard 18 vmp panel be enough voltage to run a victron 100/50? Say two 250watt panels in parallel? Will this voltage be enough if the panel wattage is noticable smaller than the combined battery charge rate + loads? In this case will the voltage sag?

Thanks

Re: Mppt want's 1.5X battery voltage to run properly?

PostPosted: Sat Sep 22, 2018 10:16 pm
by APR
Victron 100/50......
1b) PV voltage must exceed Vbat + 5V for the controller to start.
Thereafter minimum PV voltage is Vbat + 1V.

From... https://www.victronenergy.com/upload/do ... -50-EN.pdf

Is 18 volt the maximum power voltage of the panel with an open circuit voltage of around 21 - 22 volts? If so then no issues at all with the panels in parallel.

With the Victron 100/50 MPPT charge controller you could always put the 2 panels in series. I would put them in series anyway as the Victron charge controller will work well at the higher input voltage.

Re: Mppt want's 1.5X battery voltage to run properly?

PostPosted: Sun Sep 23, 2018 1:37 pm
by australsolarier
never hurts to read the manual first when in doubt or having questions

Re: Mppt want's 1.5X battery voltage to run properly?

PostPosted: Sun Sep 23, 2018 11:22 pm
by Jman
This is about mppt in general. Someone on another forum said to run properley they need a max power voltage 1.5X the charging voltage so that is 19-20volts. I have already read manual, but wanted to be sure.

Re: Mppt want's 1.5X battery voltage to run properly?

PostPosted: Sun Sep 23, 2018 11:24 pm
by Jman
Hi. Yes they are ocv 21volts.
You say the controller will work well in series. Is that really much better?

Re: Mppt want's 1.5X battery voltage to run properly?

PostPosted: Mon Sep 24, 2018 12:15 am
by APR
Have a read of the technical white paper I link to below, and especially the conclusion in part 6, “The Solution” where input voltage to an MPPT controller is discussed with respect to reduced panel voltage at high panel (cell actually) temperature, and also the fact that cable losses are reduced by increasing the voltage and reducing the amps by having panels in series instead of parallel...

https://www.victronenergy.com/upload/do ... r-MPPT.pdf

If you need to run panel cabling any distance to the charge controller, having the panels in series will minimise cable losses. These losses can be very significant, and the lower the voltage the more relevant cable length becomes. While you can use heavier cable to overcome the issue, heavier cable will be far more expensive.

Re: Mppt want's 1.5X battery voltage to run properly?

PostPosted: Tue Sep 25, 2018 6:33 pm
by Jman
[MODERATOR - removed unnecessary quoting, please stop quoting entire previous posts- see forum guidelines.]




Thanks APR, I will read that tonight. I favoured putting two panels in Parallel over series as I still don't know about if I need diodes in between or anything with shading? or can I just straight connect them?

Cheers

Re: Mppt want's 1.5X battery voltage to run properly?

PostPosted: Tue Sep 25, 2018 8:44 pm
by APR
Jman wrote:I favoured putting two panels in Parallel over series as I still don't know about if I need diodes in between or anything with shading? or can I just straight connect them?


I would expect your 250 watt panels to have bypass diodes in the junction box. If not, you could put bypass diodes around each panel as per the diagram I link to below. You ideally want an adequately rated diode (amps and volts) and preferably a Schottky diode because of the low forward voltage drop of Schottky diodes.

If you are going to put panels in parallel, it is wise to install either blocking diodes as per the diagram below, or use a fuse in place of the blocking diode, with the fuse rating as specified by the panel manufacturer. The rating of this fuse is specified in the panel specs as the “Maximum Series Fuse Rating” in amps.

https://goo.gl/images/C427vh