Alfa38User
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Which way did you set it up??
Solar panels on tent trailer - Worth it?
- Thread starter KodiakJack
- Start date
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Kevin Means
Site Team
Welcome to the world of RV solar! I'm glad it's working for you. You should only need one controller, but it has to be rated to handle the output of both panels. Without knowing the specs of your controller, I can't say whether or not it would be adequate. That isn't to say two controllers won't work. In fact, they will, but two controllers cost more, and require additional wiring.KodiakJack said:
Kev
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KodiakJack
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Alfa38User said:
2 separate controllers.
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KodiakJack
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Kevin Means said:
The panels were a two-pack of 40w panels and came with two of everything including controllers.
I thought I was going to have to monkey with wires to make it long enough to reach the battery, so I figured while I was splicing and dicing, I may as well wire them up through just the one controller. (Which does have enough capacity btw). But once I got them assembled, I realized I had more than enough cable to reach as is, so I just hooked them both up separately. I was worried they would ?fight? each other... sensing the input from the other unit and cycle off too early. But that doesn?t SEEM to be the case... I?m certainly open to guidance on that.
Voltage while charging climbed to about 14.8 for a while, then it cycled off and came back to about 13.7.
Kevin Means
Site Team
It sounds like they're working fine. PWM controllers keep the voltage up around 14.4 to 14.8 until the float phase, then the voltage is reduced to about 13.8 to keep them topped off. Happy RVing!
Kev
Kev
Ernie n Tara
Well-known member
Hi,
I'm not familiar with solar controllers but it would seem that PWM (I presume that means Pulse Width Modulated) would be quite inefficient. That is due to the fact that some percentage of the output will be lost in reducing the average Voltage. For example given 28V from the panel, reducing the charge Voltage to 14 would require shutting the output off 50% of the time (the batteries act as a filter to average the output). What am I missing?
Sorry to get off subject,
Ernie
I'm not familiar with solar controllers but it would seem that PWM (I presume that means Pulse Width Modulated) would be quite inefficient. That is due to the fact that some percentage of the output will be lost in reducing the average Voltage. For example given 28V from the panel, reducing the charge Voltage to 14 would require shutting the output off 50% of the time (the batteries act as a filter to average the output). What am I missing?
Sorry to get off subject,
Ernie
Kevin Means
Site Team
You're right Ernie, PWM controllers are less efficient than MPPT controllers (by about 30%) but PWM controllers are also significantly less expensive. There are some cheap Chinese MPPT controllers that are close to the same cost, but... well... need I say more?
PWM controllers are well suited for topping off house batteries, like Brad wants to do, because the batteries won't get drawn very far while the RV is in storage. If the batteries were going to be drawn down more, like when camping, an MPPT controller might make more sense, although the size of the array, the depth of discharge and the battery bank's total AH capacity are important considerations.
An MPPT controller's ability to convert excess voltage to amps is a real benefit when trying to pump as many amps as possible back into a more deeply discharged battery bank, however, we have to weigh the cost of the more expensive controller with its abilities. If the batteries don't have much draw on them (like when the RV is in storage) and they don't get drawn down very far, a PWM controller should easily be able to keep an RV's battery bank topped off - without having to convert excess volts to amps.
Additionally, a single 12 volt 100 watt solar panel only puts out about 18 - 21 volts under ideal conditions. Since a PWM controller charges at 14.4 to 14.8 volts in the bulk and absorption phases (which probably won't be a factor while the RV is in storage) there isn't much excess voltage for an MPPT controller to work with, and there's really no need to convert the panel's excess voltage to amps while the batteries are float charging.
Kev
PWM controllers are well suited for topping off house batteries, like Brad wants to do, because the batteries won't get drawn very far while the RV is in storage. If the batteries were going to be drawn down more, like when camping, an MPPT controller might make more sense, although the size of the array, the depth of discharge and the battery bank's total AH capacity are important considerations.
An MPPT controller's ability to convert excess voltage to amps is a real benefit when trying to pump as many amps as possible back into a more deeply discharged battery bank, however, we have to weigh the cost of the more expensive controller with its abilities. If the batteries don't have much draw on them (like when the RV is in storage) and they don't get drawn down very far, a PWM controller should easily be able to keep an RV's battery bank topped off - without having to convert excess volts to amps.
Additionally, a single 12 volt 100 watt solar panel only puts out about 18 - 21 volts under ideal conditions. Since a PWM controller charges at 14.4 to 14.8 volts in the bulk and absorption phases (which probably won't be a factor while the RV is in storage) there isn't much excess voltage for an MPPT controller to work with, and there's really no need to convert the panel's excess voltage to amps while the batteries are float charging.
Kev
