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Positive ground PWM charge controller question

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Prescott

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May 26, 2021
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Hi, I've got a question about positive ground PMW charge controllers. I'd like to install an inline fuse and a cut off switch between my 30 amp HQST charge controller and the PV panels (2 100 watt Newpowa compact panels) This charge controller is a positive ground. Normally, if this was a negative ground controller, I think I should put the fuse on the positive cable running from the PV panels and the cutoff on the negative cable, but does the fact the charge controller is a positive ground change either of those placements?

Also, with a positive ground controller, can I still safely put a second cut off switch on the cable between the battery's negative post and the vehicle chassis, in order to kill all the circuits powered by the battery, and an inline fuse on the battery's positive cable that powers my fuse block?

This system is being installed on a vehicle with a chassis ground.

I'm a real newbie with all of this, so i appreciate any and all advice. Thanks!!!
 
Prescott said:
This system is being installed on a vehicle with a chassis ground.
Click to expand...
Just to be clear, this is a vehicle where the chassis ground is positive and not negative?

I have never dealt with positive ground before, but positive ground can be used in some applications, I hear for pipes, or some foreign vehicles may come that way.
 
Hi, thanks for responding! The vehicle's factory-installed electric system is negative grounded to the chassis and powered by an alternator. I'm adding a PV system that will be isolated from the factory electrical system - except for sharing the chassis as the ground.

Once the PV system is in, I'd like to ground the solar system's battery's negative post to the chassis as well. I will be running a number of electrical items (fans, water pump, some lights) off the solar system's 122 AH battery. Apart from sharing the chassis as the ground, the PC system and the vehicle's factory electric system will be isolated from each other.

My concern is the charge controller is a positive ground model. I saw elsewhere on this forum that a positive grounded charge controller doesn't mean the whole system is positive grounded and it really only applies to the circuit between the panels and the charge controller. I think I understand that, but I want to make sure the cutoff and the fuse between the charge controller and the pv panels goes on the correct wires.
 
hi, the model no. is PWM30LCD

I haven't been able to find any documentation on the charge controller on the HQST website.
 
Hi Bud, thanks for helping! Yes its the one in post #6. By googling the model number (something I didn't think to do until you asked what it was), I found a Renogy solar controller with the same model number, and found the manual on Renogy's website. There is no photo on the manual, so I can't tell for certain if it is for the same device that HQST sells under the HQST brand. In any event, the Renogy manual's installation instructions are extremely basic, and don't show or mention installing any in line fuses or cut offs.

I'm pretty set on adding an in-line fuse and also a cut off between the panels and the controller, as I think its better and safer than just running a cable directly from the panels to the charge controller. I admit, I'm a newbie, so maybe the consensus is it is a bad idea to add an in-line fuse or cutoff, but I can't imagine that's the case.
 
Unless you want to blaze new trails, may want to get another $30 PWM that’s grounded negative. If not, I’d try to avoid using a frame ground and just use wires.

Without having ever dealt with it, what I’m picturing in my head, which is certainly not based off any real experience or knowledge of positive and negative grounding working together, is nothing good happening.
 
The reviews on this controller look pretty good, and it seems like many have used it on vehicles so I'm hoping I can keep it. Maybe I'll put an in line fuse in both the positive and negative cables between the PV panels and charge controller to cover both possibilities.
 
Not a good idea......if you short the data USB port frame or any other part of the unit to the vehicle ground you will release the magic smoke from the unit from which it will never recover. Nuff said
 
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