Max Temp Compensated Charge Voltage

[Boompy]

Hi all,

I'm curious as to the maximum charge voltage of the Midnite 150.

Assuming I need a temp compensated charge voltage in the order of 32V (seriously cold temps) utilising a sting voltage of 29V, is this achievable?

I have to keep my string voltages low (that's a whole different subject) but wattage will sit around 700W @ 19A.

Can anybody shed some light on this one?

[Vic]

Hi Boompy,

Have not looked at your previous Posts ...

So,   assume that you have a 24 V battery,   and  are trying to use "strings" of one PV  --  all PVs in parallel,  perhaps.

If the above is the case,   it  would not be possible to fully-charge Lead Acid (LA)batteries.

It your system is 24 V,   and you have LA batteries,   you would want an input voltage to the Classic of at least 130%  of the highest Temperature Compensated charge,  or EQ voltage.

If your PVs are 60-cell modules,  then strings of two PVs would be  ideal,  on a 24 V system,   AND,  really would be the minimum input voltage with a 24 V battery and PVs with an STC Vmp of around 29 V.

Are the above assumptions close to what your system configuration is,   and what you were asking?

Please give details of your system components,   and exactly what are your concerns in using them.   Also,  please describe the nature of your system (off-grid,  grid backup,  RV,  etc).

Have you had a chance to use the Classic String SIzing Tool (?):
http://midnitesolar.com/sizingTool/displaySizing.php

Thanks for the added info,   Vic

[Boompy]

Hi Vic,

Thanks so much for your detailed response.

I am operating a 24V AGM battery system in a mobile application. Keeping PV voltages as low as possible is advantageous from a legislative perspective but not critical. I use the PV for absorption and float, as I have a generator for bulk purposes.

Yes you are right, I am operating 2 x 275W single strings of panels.

So is 130% of the highest temp comp. voltage the best choice from an efficiency perspective, or is it just not possible to operate the CC in a 'boost' condition?

Thanks again for your input

[Vic]

Boompy,

To fully-charge a 24 V LA battery,  you have no real choice.   You really MUST run two of your PVs in series.  Even if your 275 Watt PVs  were 72-cell modules,  with an MPPT Charge Controller (CC),   most likely,   you would not be able to fully charge your AGM batteries.

On some days,  you could probably get a full charge,   but only with 72-cell modules  (and,  at 275 W,  your PVs probably are NOT 72-cells).  It would be best (IMO)  to run string/s of two PVs in series,  particularly,   if  those PVs have 60 cells.   Sixty cell PVs  have STC Vmps from about 29,  to about 31.5 volts.   Even with 72-cell PVs (STC Vmps of about 35.5 -  36.5 V),   the CC  would tend to produce sub-par  power,     under certain weather conditions  --  warm/hot PVs  and cool batteries would be one of the worst-case conditions for this reduced power production.

So,   all-in-all,   the Classic would be most efficient with two PVs in series,  per string.  This is where efficiency includes maximizing power production under almost any possible weather condition (and not just the power-loss efficiency factor,  within the CC).

Again,   FWIW.    Vic

[mike90045]

...or is it just not possible to operate the CC in a 'boost' condition?.....

The Classic only does downconversion, it does not boost voltage