I have a sizing question.
I have a module with a VMP of 26.30. Can I charge a 12V battery bank with this module using the Brat?
it needs to be a true 12 volt panel to be efficient with PWM, IMHO I feel it would maintain a 24 volt battery bank.
In the Brat manual it says that a "12V panel (usually has a VMP of 17V or more)"......how much more is my question?
The spec sheet says a maximum input of 60VDC.
The Brat will tolerate up to 60v. I have several customers who are charging a 12v battery using a 250 wat 60 cell 37 volt module. They know they are not getting the 250 watts but the module is cheaper for them then a 120 watt 12v module so they put it in.
Thanks Halfcrazy for the information.....sweet.
In ballpark terms how much less would the 250 watt 60 cell 37 volt module produce?
Well probably the best way to look at it is you would get the short circuit current as the max. So if the module is around 8.5 amps of current at ISC then you would get 8.5 amps out into the battery or around 120 watts
Ryan, that is the best answer I've heard in quit some time, the answer normally I hear is you just can't do it with a PWM controller but I have as you know with success.
Walt
When you have a mismatch between PV and a PWM CC the best you, as Ryan put it, will get is the nominal Voltage times the ISC,
whereas MPPT gives you the most it can produce at the nominal voltage, usually that is near the discounted watt rating,
but what it comes down to is:
the cost which is the value to you of the inaccessible power of what you do not get to use, or the wasted $$ between the amount the PWM and the MPPT can make.
ADD: taking into account the difference in cost of the 2 types of CC and the cost of different panel(s) that can are available for use
a value judgment, and not a clear one till the cows come home... ;)
WB ;)
I still have much to learn! 8)
Quote from: Westbranch on February 03, 2016, 05:32:30 PM
When you have a mismatch between PV and a PWM CC the best you, as Ryan put it, will get is the nominal Voltage times the ISC,
whereas MPPT gives you the most it can produce at the nominal voltage, usually that is near the discounted watt rating,
but what it comes down to is:
the cost which is the value to you of the inaccessible power of what you do not get to use, or the wasted $$ between the amount the PWM and the MPPT can make... a value judgment, and not a clear one till the cows come home... ;)
Right but if you are designing a system that needs say a 75-120 watt module and the cost of a 250 watt module is cheaper than it can make sense but you have to look at all the details
I agree Ryan, I thought I covered that in the cost assessment part...Ii'll look it over bit...
Halfcrazy
Could I use 2 of the above modules with a VMP of 26.30 and a ISC of 8.2A with a 24V nominal battery bank? If so, series or parallel with the Brat?
As always thanks for the help.
Peace
Marc,
The voltage will be too low for parallel connection as the absorb voltage needs to be 28.8 or so plus a few volts for the controller. In series you might go over the high voltage limit on the brat on that surprise cold freezing morning when v.o.c. soars up 20 % or so. 52.6 volts VMP is too close to the 60 volt limit of the brat.
Been there done that with first solar CdTe panels that are rated 67 v.m.p. , 92 v.o.c. , freezing dawn had the voltage over 100 volts and cooked my BZ -500 controller at the crack of dawn!
Be careful with over voltage on the input......usually fatal to the controller........leaves evidence of the over voltage event.......not covered by warranty by any manufacturer of controllers......AFAIK!
Good job on Doctors Without Borders..........thanx for your dedication.........
dave
I recently bought a brat charge controller ,so to my understanding if charging a 12 volt battery its best ( more efficient) to use solar panels that are around 17-21volts open circuit voltage (called 12 volt panel ,36 cell) and hook panels in parallel and if charging a 24 volt battery it's best to use a solar panel 60 cell ( with a open circuit voltage of 36 volts ) and also hook panels up in parallel as long that in both cases the voltage doesnt go over the 60 volt limit of the charge controller and of course the max of amps of 30 as long as the additional wire is installed according to the brat manual to use the brat as a 30 amp charge controller