Suitcase Case via 7 pin connector pigtail?

[KarenPDX]

Has anybody done this with a suitcase solar panel? On my 21C there's a Victron DC/DC charger in-between the 7 pin plug and the battery busses.

Is my thinking right that the Victron unit could function as a charge controller for the battery or should I use the onboard charge controller as well?

We are headed to AZ in a couple of days and I'm hoping to do some experiments to find the best way to use a suitcase solar panel on my rig.

The Renology unit is easily configured to use the onboard controller or by pass it so I though I would do the following and look at the current flowing across my shunt.

1) Solar suit case wired in parallel with the roof top panels and the solar side of the GoPower charge controller. (The factory wired auxiliary solar port)

2) Hook up the solar suitcase to the battery side via a seven pin pigtail connector to the the trailer wiring. Use of onboard charge controller on the suitcase pending input from the community.

3) Direct connection to battery bank of solar suitcase. Suitcase charger controller in use.

4) As above, but wire battery bank with standalone charger controller and then hook the suitcase to the standalone charge controller.





Regards,


Mike

[SteveSgt]

I predict your #2 would be problematic. The DC-DC converter in my 21C takes time to boot-up, and draws all of its operating power from the input side, not the "house battery" side. So unless you're in a situation with reliable direct sun for long periods, you might not get much of a charge. Also, these DC-DC devices are not nearly efficient as an MPPT solar controller, so there will be even more losses there.

I have done your #1 and it did work. I predict if I had a big charge deficit it might not be the most efficient option because my suitcase panels have a lower Vmp (voltage at maximum power) than the panels on the roof.

Your #3 should work fine if you have access to do it.

In the not-so distant future I will rewire my solar system resembling your #4.

[alanmalk]

Originally Posted by KarenPDX

Has anybody done this with a suitcase solar panel? On my 21C there's a Victron DC/DC charger in-between the 7 pin plug and the battery busses.

Is my thinking right that the Victron unit could function as a charge controller for the battery or should I use the onboard charge controller as well?

We are headed to AZ in a couple of days and I'm hoping to do some experiments to find the best way to use a suitcase solar panel on my rig.

The Renology unit is easily configured to use the onboard controller or by pass it so I though I would do the following and look at the current flowing across my shunt.

1) Solar suit case wired in parallel with the roof top panels and the solar side of the GoPower charge controller. (The factory wired auxiliary solar port)

2) Hook up the solar suitcase to the battery side via a seven pin pigtail connector to the the trailer wiring. Use of onboard charge controller on the suitcase pending input from the community.

3) Direct connection to battery bank of solar suitcase. Suitcase charger controller in use.

4) As above, but wire battery bank with standalone charger controller and then hook the suitcase to the standalone charge controller.

Regards,
Mike

I see a potential issue with using the Victron DC/DC converter with a solar panel. The reason the DC/DC converter is in the circuit in the first place is to boost the voltage from the tow vehicle to a voltage suitable to charge Lithium batteries (around 14.4 to 14.8). Tow vehicles - mine included - are not designed to get the correct voltage from the alternator all the way back to the trailer batteries. The DC/DC boost function expects a lower voltage coming in as opposed to the voltage going out (12 V in and 14.6 V out, for example). Whereas the panel - with its internal controller bypassed - should be providing typically 18 V or more if unloaded. I don't know about the Victron specifically, but I do know that some DC/DC converters will pass the higher voltage without any regulating - potentially applying 18 V to the batteries and anything running.

I personally use the #1 solution - for the last 8 years. Parallel the unregulated remote panel voltage to the GoPower regulator. It is quite happy with the extra power and I watch the current about double going into the batteries.

[KarenPDX]

I would like to thank both of the people who replied.

There’s only 0.1 volt difference in Vpm between my rooftop panels and my suitcase unit and the wiring into the solar controller is a lower guage and shorter than the circut through the DC/DC Victron unit. So I will try this route 1st.

To be honest the way the Victron unit was installed it looks like it got overlooked during the trailer wireing step and was just spliced into the hitch wiring under the bed as an afterthought.

Best practice would be to mount verticlily and as close to the battery bank as possible and my install was neither.

When we come back I will think about redoing it.

[alanmalk]

Originally Posted by KarenPDX

...
To be honest the way the Victron unit was installed it looks like it got overlooked during the trailer wireing step and was just spliced into the hitch wiring under the bed as an afterthought.

Best practice would be to mount verticlily and as close to the battery bank as possible and my install was neither.

When we come back I will think about redoing it.

Vertical is good for cooling.

Being close to the battery is not necessarily a good thing. Its prime function is to pull enough amps from the alternator as to overcome voltage drop in the system and charge the Lithium batteries. So there will be (a guess) perhaps 30% more amps going in as coming out. But the outgoing voltage will be (a guess) 30% higher than the incoming. So there is no advantage to those high amps going all the way from the alternator to the battery area. But in reality it should be mounted where you can see it when necessary. The other function is to prevent the trailer battery from charging the tow vehicle battery - a diode in effect - although a very expensive diode.

Someday - perhaps - I will be installing a DC/DC converter in my tow vehicle near the hitch. Tacoma voltage drop is horrendous.