HI All, we have a 600 watts of solar panels on the roof of our Coaster, they are 2x 190watt house panels (24volt) and the rest are 12v types normally found on RVs....., our controller is 60 amp and can handle over 24volts and seems to manage to bring in mixed voltages without any problems, throwing a few towels over various panels shows them all working well at the controller. My question is about the 24 volt panels, I expected them to bring in around 10 amps each, however they only produce 5 amps each, this bothered me until I had a look at the formula amps=watts/volts, you can see by swapping the 24 volts for 12 volts you get twice the amps.
My question then is am I somehow losing half the currect (seems logically unlikely) or is it that the controller is just showing what is coming in and then when it converts it down to 12 volts (13.8) it magically jumps it back up to 10 amps??.. which is not shown on my display.
More information is necessary before we could answer the questions but a few ideas to kick off. Give us the make and type of the reg/controller and the specs off the back of the panels.
First what voltage does your system run at, 12v or 24 V, or both. Are the house batteries and the bus batteries connected or seperated.
House panels are often 24v but have less cells than battery charging panels and produce less voltage. Only 60cells instead of 72. That limits the maximum voltage available if charging 24v batteries and that is not good despite what some places say.
Battery charging panels as said should have 36 cells for 12v and if two panels are put in series to add the voltage for 24v they will put out more voltage than house panels under the same conditions and will not match them very well into the same regulator. There is a mismatch there and MPPT regulators will be confused, or if the 24v panels and the 12v panels all just feed into the same regulator for 12v output then the 24v panels are just wasting half their output no matter what probably.??
Then the regulator may be of two basic types. A simple switching type which just turns on and off to control the voltage and no boost of the current. Or a MPPT type which can take a higher voltage and "convert" it to a lower voltage and increase the current proportionally. ( Note there are cheap fakes out there also). What type do you have. There will be no boost to the current if the 24v house panels are charging into 24v batteries and not much charge at low solar levels from them. Not enough cells.
Cheers Jaahn
-- Edited by Jaahn on Sunday 31st of January 2016 06:16:46 PM
-- Edited by Jaahn on Sunday 31st of January 2016 06:21:02 PM
hi, yes I'm running both house and rv types, ie 12 and 24 volt systems. I get plenty of power to run my 12 volt hot water, lights, fridge etc, was just wondering about the amps issue.
I do not really understand your setup. So I cannot give any sensible answer.
Do all the panels just go into the one controller which is connected to a 12volt battery(s) setup?? If so then the different types and voltage panels are a mismatch and some will not give their full output. The panels cannot give more than their maximum amps no matter what voltage they are putting out but the voltage can vary. So if the 24v panels are into a simple 12v controller and 12V battery then you will only get half their power as the higher voltage is wasted.
A 24V 190W panel will only put out about 5+ A. It cannot put out more amps. A good MPPT regulator/controller can take that output and make it into 14V and 10A for charging(roughly speaking). However if you have some 12V panels connected also then it will be confused and who knows what will happen. But I think you will get the least amount of amps from each of the two types of panels.
as Jaahn has indicated we do need a little more info before we can really offer you much help, but in the mean time we can make some suggestions:
1. If you have a mix of 12V and 24V panels going into the same controller, it may be that they have set the 12v panels in series (just like two batteries end to end) this has the effect of doubling the voltage, thus all panels may be presenting the correct voltage to charge 24V (typically about 28v).
2. If your charger is a PWM (Pulse Width Modulation) controller, it just chops the voltage back to what you need to charge your 12V battery (assumes a 12v system), thus it will be wasting a fair bit of your power.
3. If you charger is a newer MPPT (Maximum Power Point Tracking), it sets the environment to maximise the output of the panels, then converts the input to the optimum voltage to charge your battery, thus you will be getting a much higher output. You can adjust most MPPT controllers to show you input voltage and current, and then on another screen output voltage and current, if the output current is significantly higher than the input current you have an MPPT.
If you could tell us the following info it would help us be clearer as to what and how:
HI Steve
A few simple answers on your part will allow this to stay on the right track
[1]Why have you got some 24V panels?
[2]Do you have any 24 Volt systems in the vehicle [starting batteries for instance??
[3Do you have just ONE regulator with all the panels[12V & 24V ]feeding into it?
4]Who wired up the panels
[5]Are the two 12V panels connected in series??
Clear answers will allow us to give you relevant info.
My question is about the 24 volt panels, I expected them to bring in around 10 amps each, however they only produce 5 amps each, this bothered me until I had a look at the formula amps=watts/volts, you can see by swapping the 24 volts for 12 volts you get twice the amps.
Simple answer, you have things the wrong way around. Twice the voltage means half the current for the same power.
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PeterD Nissan Navara D23 diesel auto, Spaceland pop-top Retired radio and electronics technician. NSW Central Coast.
