Using a second portable solar panel?

[Molly 3]

Due to limited roof space I want to use a portable solar panel alongside my roof sp panel .this means I will be using 2 separate charge controllers one mppt and one pwm To the same battery. Will this cause conflict's ,between the controllers ,or would it be OK both sp are 100 w .the roof panel has the factory fit Sargent unit that charges both engine a hab battery's but it only takes 120 w max .

 

[Wully]

I think you can fit a plug and run them both through the same controller seen phil fit similar to rugby Ken’s van a few weeks back you might have to upgrade your existing controller though I’m no expert but I think it can be done.

 

[delphin]

Fit a 12 volt plug on the freestanding one. Run the cable from the fixed one through a junction box with a 12 volt socket fitted and connect the wiring (+ to + and - to -). When you need more solar power, just plug the spare one in.

Been using that system for years and it works well.

 

[Molly 3]

Fit a 12 volt plug on the freestanding one. Run the cable from the fixed one through a junction box with a 12 volt socket fitted and connect the wiring (+ to + and - to -). When you need more solar power, just plug the spare one in.

Been using that system for years and it works well.

Problem is the original sargent factory fit controller is 120 w .total sp watts is 200 w so too high for the original controller

 

[Okta]

I am no expert but would think that 2 controllers would confuse each other. A controller is there to protect the battery from overcharging and should be monitoring the battery voltage. If there are 2 controllers they could be reading the voltage output from the other one, not the battery. My guess is that the more sensitive controller will shut off from charging, mistaking the output from the other one as a full battery.

 

[clarkpeacock]

Due to limited roof space I want to use a portable solar panel alongside my roof sp panel .this means I will be using 2 separate charge controllers one mppt and one pwm To the same battery. Will this cause conflict's ,between the controllers ,or would it be OK both sp are 100 w .the roof panel has the factory fit Sargent unit that charges both engine a hab battery's but it only takes 120 w max .

On larger scale, but makes interesting reading https://www.morningstarcorp.com/parallel-charging-using-multiple-controllers-separate-pv-arrays/

 

[Yeoblade]

I am no expert but would think that 2 controllers would confuse each other. A controller is there to protect the battery from overcharging and should be monitoring the battery voltage. If there are 2 controllers they could be reading the voltage output from the other one, not the battery. My guess is that the more sensitive controller will shut off from charging, mistaking the output from the other one as a full battery.

I thought that too, I have another 260W unit that I can't fit permanently due to lack of roof space but was going to carry it and plug in as necessary. I have 175w on the roof. I have a cheap PWM controller with it so may experiment what happens with 2 controllers and see where the current flows, though it would be better, I'm sure connected into the exisiting MPPT in series ,as they are 30v and 12v panels.
I did not install the roof panel using the existing factory solar inputs because it was too powerful anyway, rated at 100 W like OP

 

[Okta]

On larger scale, but makes interesting reading https://www.morningstarcorp.com/parallel-charging-using-multiple-controllers-separate-pv-arrays/

Interesting but the key points include identical controllers designed for parallel operation and set to the same charging profiles. This suggests to me that mixing ordinary mppt and pwm controllers is not going to work.

 

[Admin]

Unless the controllers are made for parallel operation there is a problem running two or more chargers on the batteries. One controller will read the charge voltage of the other controller as the batteries voltage and reduce the charge and the other one will be doing the same.

We actually did a real-world test with a member's set up. He has 2 panels and 2 controllers that were both identical. We looked at the charge current with both controllers connected, then we pull the fuse on controller A and the current stayed the same. We then replaced the fuse for controller A and pulled the fuse for controller B, the current stayed the same.

The best way is to have all the panels the same voltage and run them through one controller, this is what we did on Ken's van. His roof panel and portable panel are the same voltage, the roof panel is connected to the input of his solar controller and then we installed an extension with a plug on it to the same point so he could connect his portable panel. For this to work the panels must be the same voltage.

In your case Barry you need to forget about the Sargent controller and buy a Victron MPPT controller. You can then run the roof panel and your external panel through the same controller.

 

[Yeoblade]

I tested adding another panel, with the 2 in series, banging in nearly 20 amps with the sun out!