solar panels and vmp for 24v system

[totfcboatski]

whats the minimum reliable vmp a solar panel needs to charge a 24v battery bank.. im shopping and want to make a good choice
thanks!
Jeff

[Sunking]

Jeff there are two ways to go about this, and depends on what type of controller you use either being PWM or MPPT.

If using PWM dictates you use panels made for 12 volt battery systems. So if you are going to operate at 24 volts you would use two panels in series. Vmp of 12 volt battery panels average 17 volts, so for 24 volt systems you want 34 to 36 volts total if using a PWM controller with 34 being the sweat spot. Whatever you do is do not go over 36 volts using PWM on a 24 volt battery system. Reason is system losses. For example a 100 watt panel operating at 34 volts is turned into a 70 watt panel. a 100 watt panel @ 36 volts turns into a 66 watt panel.

For MPPT controllers things are a bit more flexible. Depending on the controller spec you can use up to around 120 to 130 Vmp (150 Voc) for 12, 24, 36, 48 volt battery systems. But as a minimum voltage the same PWM rule applies, so 34 volts is the minimum

[totfcboatski]

hmmmm

my c/c is a rogue thirty amp with a 60 volt max. I have talked to the owner and he recommends that I stay in the low 50's voc as im in a cold climate
i was looking at a canadian solar model cs6p-230 with a vmp of 29.60 and thought that would be suitable for my 24v battery bank.. but you think thirty four is the minimum for charging?? guess I willkeep looking!
thanks sk
jeff

[Sunking]

You need at least 31to 32 volts just at the battery terminals, plus the voltage drop of the controller. So yeah 34 minimum.

Keep in mind when referring to battery voltages we are talking nominal voltage with no charge and under a load. For a lead acid battery chemistry 100% capacity at rest is 12.6 volts and requires a source of at least 16 volts to charge it.

[totfcboatski]

ok

Yeah your correct as usual... just saw a good deal and wa trying to talk myself into jumping on it. Will keep my money in the pocket till i find something around thirty four vmp. as an aside my new penn brand SPG battery tester is giving me erroneus rvading and the float doesnt float anymore. any recommendations on a more reliable spg tester under 50 bucks?? Ive been looking and havent found any and really enjoy gathering data and doing the right thing by my new rolls battery (is it rude to name drop battery mfg's ?? lol)
thanks!
jeff

[Sunking]

as an aside my new penn brand SPG battery tester is giving me erroneus rvading and the float doesnt float anymore. any recommendations on a more reliable spg tester under 50 bucks??

Yeah try this one out for $10. Also check Lab Glass manufactures out.