Advice on deep cycle setup?
Hello, I have a Safari van that I've converted into a camper. I replaced the starting battery with a Duracell Ultra Dual Purpose (Starting/Cycling) Battery that cost $105 (got it at batteries ...
Forum Discussion
BFL13 wrote:full_mosey wrote:
Now that you mentioned MPPT, here are the salient points:
1. Watts do matter! This is different from the Isc/PWM situation.
2. With MPPT and a 200W panel and 14.4V charge, you calculate charge Amps as 200W/14.4V = 13.8A. If the MPPT is 96% efficient the result to the battery is 13.8 * .96=13.3A.
3. MPPT simplifies panel selection because it allows you to focus on fitting panel(s). You might want to look at 24V panels on solarblvd.com. You will be amazed at the $/W difference from 12V panels. This is where MPPT shines.
HTH;
John
You forgot that with MPPT you must first allow for panel heating, so knock 10% off the rated watts for that. Then something for line loss panel to controller. Now you have controller input watts. Then you deduct for controller efficiency. Now you have controller output watts. There should not be any line loss controller to battery but in some installations there will be. Now divide output watts by rising all day battery voltage and get your amps to the battery as they get less as battery voltage rises.
200w becomes 190w with panel heating, say 2% line loss so now at 186w input, 96% of that is 179w output
179/13.0 = 13.8 amps
179/13.5 = 13.3 amps
179/14.0 = 12.8 amps
179/14.4 = 12.3 amps
However once the batts are 14v it is very soon after they hit 14.x your Vabs and now you exit Bulk with its MPPT are now in Absorb doing PWM.
Thanks for the additional info and calculations. As you know, the reduction of Watts is caused primarily by the heat causing the panel to drop Volts in the formula Vmp * Imp = Watts. Panels have their own specs and you can calculate the drop when given a temperature of the panel.
Your calcs would be true even if the panels were two 100W panels with specs of Vmp 100V and Imp 1A in parallel. I have seen such panels at sunelec.com. I would not do this, but use this only to pose a question.
With PWM you would only have a 2A charger.
Are you suggesting that the MPPT will perform as a PWM in Absorption and only deliver 2A?
HTH;
John
