Backfeeding a power supply

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While playing around with my battery setup last night, I ran into something unexpected.

Here's my setup.

Powerwerx SS-30DV power supply with 2 power pole connectors on the front.
Radio is plugged into the bottom power pole.
Battery is charging off of the top power pole. Charge controller showed that it was receiving power from the power supply as well as the radio was functioning fine.

Well, I was done for the session and I turned off the power supply.

To my surprise, the radio remained on. It took me a second to realize that the battery was backfeeding the power supply and the radio was running off the battery. Completely unintended on my part. I just assumed that once the power supply was turned off, it wouldn't pass power. But then I thought about it. The power poles are obviously on the secondary side of the power supply and so are isolated from the switch.

So a couple questions.

1. I didn't even think about it, but I assume it is best practice to remove the battery connection from its charging source once the charge is complete. Am I correct here or does it really matter?

2. Am I hurting the power supply by backfeeding it from the battery?

3. Are you surprised that the two power pole connectors on the power supply are connected?


Thanks
 
The answers all depend on the circuit design of the power supply which we don't know. So, I'll give my best guess or the safest answer.

1) Yes, unplug the battery before turning the power supply off. At a minimum, the power supply will probably present a slight drain on your battery and over a day or week or month discharge it.

2) If the power supply has a crappy design, yes you can hurt it by back feeding it. I highly doubt this is the case. Don't worry about hurting it.

3) Not surprised. I would expect them to be connected in parallel with at most a fuse separating them.

Does it really only weigh 3lbs?!?!?!? All I have are old linear supplies I picked up at ham fleas and they weigh a ton. I may have to join the modern world as sometimes I'll bring my rig on a vacation we drive to.
 
While playing around with my battery setup last night, ... I turned off the power supply.

To my surprise, the radio remained on. It took me a second to realize that the battery was backfeeding the power supply and the radio was running off the battery. ...

1. I didn't even think about it, but I assume it is best practice to remove the battery connection from its charging source once the charge is complete. Am I correct here or does it really matter?
... 1) Yes, unplug the battery before turning the power supply off. At a minimum, the power supply will probably present a slight drain on your battery and over a day or week or month discharge it.

Why guess? Get out a microammeter and see if the power supply provides a measurable load on the battery when it's turned off.

2. Am I hurting the power supply by backfeeding it from the battery?
2) If the power supply has a crappy design, yes you can hurt it by back feeding it. I highly doubt this is the case. Don't worry about hurting it.
3. Are you surprised that the two power pole connectors on the power supply are connected? ...
3) Not surprised. I would expect them to be connected in parallel with at most a fuse separating them. ...

I can't find a schematic online, but any one of the three terminal pairs is specified to be able to supply the entire maximum steady-state and peak currents. This implies to me that every component downstream of the power supply proper is sized to handle the peak load, which is cheapest to implement if the only downstream components are the wires and terminals.

Take the lid off and I bet you find that all the terminal pairs are wired in parallel without even separate fusing. Or call West Mountain and ask them.

I use one of these in my setup. The power supply keeps the battery charged without overcharging, and it keeps the radios live during a power outage.

http://ki0bk.no-ip.com/~pwrgate/LLPG/Site/LLPG.html

View attachment 159492
Ok, that is pretty cool!

First there was the West Mountain Radio PWRgate PG40:

0965.jpg


Two low-loss Schottky diodes in a heat sink.

Then there was the West Mountain Super PWRgate PG40S:
2719.jpg


Same kind of diode isolator, plus a fancy battery charger (trickle/bulk/peak voltage/float, to use their nomenclature).

The Flint Hills (KI0BK) device claims to have a "trickle charger", which would put it somewhere in between in terms of sophistication. They do allude to using FETs instead of diodes for load switching, which is what allows them to enclose the circuit board in a plastic box instead of a finned heat sink.

I note that KI0BK uses the mark "PWRgate". I bet West Mountain is kicking themselves for not trademarking that when they had the chance.


Keep in mind that many stations with multiple 12VDC devices probably don't depend upon power supplies with multiple Powerpole pairs. I get the impression that lots of folks buy (or make) power strips with separately fused outlets: West Mountain RIGrunner. MFJ also makes a number of models (some with 5-way binding posts instead-of/in-addition-to Powerpoles; some with meters): DC-->Power Distribution, Multiple Outlets.

I have the first generation of one of these: West Mountain RIGrunner 4010S:
6528.jpg

In "auto" mode, it supplies power to outlets 1-9 only when it senses current drawn from the master outlet (the rig). So, turning on the rig energizes the rest of your gear, and turning off the rig turns off everything else. (No USB interface, no automobile delays, etc).
 
I use one of these in my setup. The power supply keeps the battery charged without overcharging, and it keeps the radios live during a power outage.

http://ki0bk.no-ip.com/~pwrgate/LLPG/Site/LLPG.html

View attachment 159492

Okay, that switching circuit has to be pretty simple. I'm no power supply designer but I'm guessing that just keeps the battery OFF until the power supply voltage drops below the battery voltage, at which point the MOSFET turns ON and away you go on battery power.
 
Big diode in series with battery (+) lead? Don't forget the 0.6v drop across the diode. Should keep battery from back feeding the PS.
 
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