[aprssig] Are solar charge controllers a safe powere tap?

spam8mybrain spam8mybrain at yahoo.com
Tue Sep 12 17:35:56 EDT 2017

Interesting results of your suggested experiment. I took the AM radio to the inverter compartment as you suggested, in daylight, and found a sharp-edged hum (but only inside the compartment, near the heavy wires). I turned off the disconnect switches at the input and output of the solar charge controller (taking the charge controller and panels completely out of circuit). No change. I turned off the "salesman's switch" to supposedly turn off all the RV coach power. No change. I turned off the master disconnect switch in the engine compartment. Still no change. And the hum was also in the battery compartment, but only near the cables running to the inverter, and near the battery control box in the battery compartment (contains relays for jumping the coach batteries to the engine batteries for jump-starting, and other heavy switching relays).
I'm not sure if that was all backfeed from the MSW inverter/charger or something else (this vehicle does have a parasitic battery charge leak I haven't tracked down yet).
So, I have hum, but don't know if it's actually on the battery lines. I guess I need to get a battery-powered AC-coupled oscilloscope down here to check the actual wires.
I never actually had a power noise problem with my Kenwood D710 in this vehicle, but it was connected to the factory-installed CB radio power feed at the driver's position (dozens of feet and a couple of fuses away from the engine [not coach] batteries).
Andrew, KA2DDO

-------- Original message --------
From: Robert Bruninga <bruninga at usna.edu> 
Date: 9/6/17  17:22  (GMT-05:00) 
To: aprssig at tapr.org 
Subject: Re: [aprssig] Are solar charge controllers a safe powere tap? 

A simpler first cut approach would be to take a portable AM radio and hold
it in the Inverter compartment. At night and again during the day when the
sun is charging the battry.  Sure, getting your DC from there is just fine
with the 2/0 cable.  Its just going to be how much noise is tolerable and if
there is that much at the inverter, then going 5 feet away to the battery is
not going to make that much difference.

Best to find the noise, and filter it at the inverter in the first place.
Then you can tap in there too.
Bob, WB4aPR

-----Original Message-----
From: aprssig [mailto:aprssig-bounces at tapr.org] On Behalf Of al wolfe
Sent: Wednesday, September 06, 2017 5:07 PM
To: aprssig at tapr.org
Subject: Re: [aprssig] Are solar charge controllers a safe powere tap?

    Solar controllers are notorious for generating noise. They mostly use
switch-mode control. That said, some are better than others. Your best bet
would be to measure the noise at the controller and at the battery terminals
with an oscilloscope or lacking that, a sensitive AC voltmeter. Much of the
noise can be filtered out with LC networks in the power line to the radio.
Other radiated noise is going to be difficult to deal with.

    Generally, getting power at the battery works the best as the battery is
usually bonded to the trailer frame near the battery. Also, the battery
typically has the lowest impedance to noise of any part of the electrical
system. Often the battery charging system is not directly bonded to the
frame and relies on the negative lead to the battery for grounding.

    The bottom line is that all bets are off as every situation is
different. You will need to try various grounding, bonding, shielding, and
filtering until the noise is at a livable level.

    Good luck with this.

Al, k9si

> Subject: [aprssig] [off-topic] Are solar charge controllers a safe
> 	power tap?
> Greetings, all.
> This might be a little off-topic, but I'm having difficulty finding a
> wiring path in my RV to get direct battery power for my rigs
> (especially my remote monitoring APRS project), and wanted to bounce
> an idea off the collected wisdom.
> The battery compartment on my motor home is pretty isolated from the
> passenger areas, so I was looking for an easier/safer place to tap. I
> had had a solar power system added to the motor home, and the charge
> controller (a Blue Sky MPPT controller) is mounted in the inverter
> compartment (5 feet from the battery compartment) with 2/0 cable
> linking the charge controller output to the coach battery terminals.
> Since it is much easier to get to the charge controller than to the
> batteries (in terms of running more cable), I was wondering if it
> would work to parallel off the charge controller output, or whether that
> would inject too much noise into the radios.
> Any advice welcome.
> Andrew Pavlin, KA2DDO
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