Renogy DC-DC MPPT not an isolator?

[critical367]

I installed a Renogy 30A DC-DC/MPPT combo and it works well. The one glitch is that it seems to draw around 2A when the ignition is off. The charging vehicle is a 2021 Subaru Ascent and I have the ignition wire connected to the Renogy using the 12V line in the 7-way connector. Of course, if I disconnect the trailer (I used Anderson plugs at the bumper) everything is fine and that is my work around, as long as I remember when we pull over for the night.

I have a case in with Renogy about this and they may send me a replacement unit. I will see if it works better, but wonder if anyone else has noticed this.

Thanks.

 

[camelCase]

There is a voltage sensing wire that has to be connected to a keyed source so the relay inside the unit knows to stop drawing power from the starter battery. Sounds like you need to double check that.

Edit: I forgot about the computer controlled alternator your car will have. You also need to make sure the ignition signal wire is installed correctly. Check page 11 in the manual.

https://www.renogy.com/content/RBC3050D1S-G1/RBC3050D1S-Manual.pdf

 

[critical367]

Yeap, that is what I did. I connected the 12V charging wire from the 7-way connector (originally on the positive bus) to the ignition wire supplied with the Renogy unit. The red LED (#10 in the manual's diagram) did not go off when the car ignition was turned off.

 

[HRTKD]

Yeap, that is what I did. I connected the 12V charging wire from the 7-way connector (originally on the positive bus) to the ignition wire supplied with the Renogy unit. The red LED (#10 in the manual's diagram) did not go off when the car ignition was turned off.

That makes me wonder if the 12 volt power at the 7 pin is active all the time. For a modern car, that would be unusual. Is it possible that the 12v power turns off after a period of time, like 10 minutes?

Put a meter on the 7 pin outlet and check for voltage.

Maybe there is voltage but no amps?

Either way, the expectation is that your ignition wire is supposed to be wired to an ignition-on circuit, not the 7 pin 12 volt source.

 

[John Frum]

I installed a Renogy 30A DC-DC/MPPT combo and it works well. The one glitch is that it seems to draw around 2A when the ignition is off. The charging vehicle is a 2021 Subaru Ascent and I have the ignition wire connected to the Renogy using the 12V line in the 7-way connector. Of course, if I disconnect the trailer (I used Anderson plugs at the bumper) everything is fine and that is my work around, as long as I remember when we pull over for the night.

I have a case in with Renogy about this and they may send me a replacement unit. I will see if it works better, but wonder if anyone else has noticed this.

Thanks.

Non-isolated dc2dc chargers are not suitable for use in parallel with a tow cable.
The Renogy unit you mention is non-isolated.
It creates a ground loop.

You should be using an isolated dc2dc charger.

 

[brb58]

Non-isolated dc2dc chargers are not suitable for use in parallel with a tow cable.
The Renogy unit you mention is non-isolated.
It creates a ground loop.

You should be using an isolated dc2dc charger.

Disagree. Tow vehicle and trailer are on the same ground since the grounds are connected so they are the same potential.

 

[critical367]

That makes me wonder if the 12 volt power at the 7 pin is active all the time. For a modern car, that would be unusual. Is it possible that the 12v power turns off after a period of time, like 10 minutes?

Put a meter on the 7 pin outlet and check for voltage.

Maybe there is voltage but no amps?

Either way, the expectation is that your ignition wire is supposed to be wired to an ignition-on circuit, not the 7 pin 12 volt source.

I think you nailed it. There was zero voltage at the outlet contact 4 (12V accessory/charging) until the ignition was turned on, when it went to 14.1V. After turning ignition off, it remained around 11.9 - 12 V. I watched for over 10 minutes, then had to do something else. I will check again to confirm when I get a chance. Thank you.

Regarding our final sentence, the instructions are to connect to anything that is on only when ignition is on, which should be the case with the 12V source. Other wires are for lights and brakes which would not be suitable. Or I would have to run a 3rd wire to something.

 

[critical367]

Non-isolated dc2dc chargers are not suitable for use in parallel with a tow cable.
The Renogy unit you mention is non-isolated.
It creates a ground loop.

You should be using an isolated dc2dc charger.

I am not sure I understand what you mean by "parallel with a tow cable". If you mean the 12V accessory line in the connector, I disconnected it from the bus and it terminates into the IGN wire to the Renogy unit. So it is not charging in parallel. All the negatives are connected to the same bus (Renogy, battery, charging line). Does that make sense, sound OK?

 

[John Frum]

I am not sure I understand what you mean by "parallel with a tow cable". If you mean the 12V accessory line in the connector, I disconnected it from the bus and it terminates into the IGN wire to the Renogy unit. So it is not charging in parallel. All the negatives are connected to the same bus (Renogy, battery, charging line). Does that make sense, sound OK?

You have the 10 awg return wire in the 7 pin and the thick common wire from the dc2dc charger.
That is parallel return paths, which is a ground loop.

 

[brb58]

You have the 10 awg return wire in the 7 pin and the thick common wire from the dc2dc charger.
That is parallel return paths, which is a ground loop

It's not going to be carrying enough different currents to worry about. If you are really worried about ground loops, there are a hundred of them just in a car's chassis that are worse than this.

Former EE at GM so I know this intimately.

 

[bradbill]

You have the 10 awg return wire in the 7 pin and the thick common wire from the dc2dc charger.
That is parallel return paths, which is a ground loop.

Sorry...that is hardly an issue here.

If we were talking about analog signals here, you could possibly have an issue but we aren't.

 

[John Frum]

Sorry...that is hardly an issue here.

If we were talking about analog signals here, you could possibly have an issue but we aren't.

If the negative wire from the dc2dc charger ever became disconnected the 7 pin wire could melt or cause a fire.

 

[bradbill]

If the negative wire from the dc2dc charger ever became disconnected the 7 pin wire could melt or cause a fire.

Not likely...the voltage would drop so much that the DC2DC converter wouldn't even operate. Same reason why it wouldn't melt if you hooked it up straight to a lithium battery.

BTW, that 7 pin wire is protected by a fuse anyway so it would blow before any wires were melting.

 

[John Frum]

BTW, that 7 pin wire is protected by a fuse anyway so it would blow before any wires were melting.

The return wire is not fused.

 

[bradbill]

The return wire is not fused.

LOL....let's back up....if the negative wire came off the DC to DC converter, why would the 7 pin negative wire be carrying current?

Also, how would that be any different using an isolated DC to DC converter?

 

[critical367]

You have the 10 awg return wire in the 7 pin and the thick common wire from the dc2dc charger.
That is parallel return paths, which is a ground loop.

Got it! Thanks for the explanation, which lead to some more reading. The engine end of the DC-DC wire is grounded on the same chassis bolt as the lead from the vehicle battery. At the trailer, the two grounds are on the negative bus. So I hope that avoids the "potential" problem.

 

[bradbill]

Got it! Thanks for the explanation, which lead to some more reading. The engine end of the DC-DC wire is grounded on the same chassis bolt as the lead from the vehicle battery. At the trailer, the two grounds are on the negative bus. So I hope that avoids the "potential" problem.

You don't have a problem caused by your grounds.

 

[John Frum]

Got it! Thanks for the explanation, which lead to some more reading. The engine end of the DC-DC wire is grounded on the same chassis bolt as the lead from the vehicle battery. At the trailer, the two grounds are on the negative bus. So I hope that avoids the "potential" problem.

the 7 pin return is bonded to the chassis in the tow vehice and the trailer.
The dc distribution panel in the trailer is bonded to the chassis
The dc2dc charger common is bonded to the chassis in the tow vehicle and trailer via the trailer dc distribution panel.
That is a ground loop.

You could isolate the 7 pin return wire and then rely on the dc2dc charger common as the return path.
The problem with that is your trailer now has a non standard interface.

 

[bradbill]

the 7 pin return is bonded to the chassis in the tow vehice and the trailer.
The dc distribution panel in the trailer is bonded to the chassis
The dc2dc charger common is bonded to the chassis in the tow vehicle and trailer via the trailer dc distribution panel.
That is a ground loop.

You could isolate the 7 pin return wire and then rely on the dc2dc charger common as the return path.
The problem with that is your trailer now has a non standard interface.

So where does the return for his trailer lights come from?

It's all just silly. Non isolated DC to DC converters are made exactly for this scenario.

 

[brb58]

So where does the return for his trailer lights come from?

It's all just silly. Non isolated DC to DC converters are made exactly for this scenario.

I guess just form the Anderson connector but I agree...there is absolutely zero need to do that. There are going to be no ground loops created. Just ridiculous.