Can Bargman be used with Solar?

[RottieMom]

I've been doing a little research on portable solar and started wondering if I could connect solar to TM using Bargman the same way I did with Battery Tender.

Bill, what do you think? Would it make sense to change clips that attach to battery to terminal loops and just attach those to a TV bargman and then plug in TM bargman cable?

[tentcamper]

I would think it would work, but you will have some lose from the long wire from the front to the back. Only area that I would be concerned with is the wire gauge, connector contacts and length of the wire from the tongue to the rear battery box.

[Bill]

Sure it would work, and for the same reason the Battery Tender works. Both are PWM (Pulse Width Modulated) devices, meaning that they send pulses of charge current toward the battery, but measure the battery voltage between pulses, when no current is flowing. Therefore there is no voltage drop in the wires at the moment the measurment is made.

In addition, the solar charge controller is back near the battery, so even if it were not PWM, it would sample the actual battery voltage. Either way, it uses the raw (high) voltage from the panels as a source. As noted, the raw voltage will be reduced a bit by the drop in the long wires - but the raw voltage is generally on the order of 17 volts, so there is plenty of margin.

Bill

[tentcamper]

Bill, very good point. I was thinking about a potable solar panels with the controller mounted on the panels and sending the charge voltage down the wires from the Bargman.

This opens a lot of questions for me. If the controller is mounted in the back? Is there an issue wiring the controller to battery wire from the Bargman and still have the battery charge line work with the TV? Due to the Pulse Width Modulation, would there be a current loss when the TV charges via 12V charge line? Would you need a circuit or manually need to switch to bypass the solar controller?

[Bill]

Tentcamper -

I would love to discuss and speculate - engineers do a lot of that, and we enjoy it. But I haven't done what you describe, so I don't want to give any hard advice - especially since I am not exactly sure what the situation is that you describe.

Many folks have plugged the Bargman into the tow vehicle, mounted the solar controller near the TM battery, and driven down the road while the battery charges from both sources. This is legitimate, all reports are good, and I would expect them to be. There is no need to disconnect one or the other. Both sources contribute to the charge. And again, since the charge controller measures battery voltage at the battery, it doesn't see the voltage drop in the wiring between the tow vehicle alternator and the TM battery.

I don't think that you are asking about connecting the tow vehicle and the solar controller through the Bargman at the same time. I'm not sure how or why you would do that. But perhaps you are observing that the charge current from the tow vehicle is continuous - it is not a PWM device - and asking about the interaction of a PWM source and a non-PWM source. If that is something you want to discuss, we can do that.

Hope this helps, though I'm not sure if it answers the mail.

Bill

[scrubjaysnest]

This might not be a good idea with a PWM controller as the CC input is switched to the battery by turning on a FET. A MPPT on the other hand is isolated input to output; they are DC to DC with the input DC getting switched across a transformer.
I have been giving this idea some thought but our original wiring on the TM was a little strange. The Bargmen 10 awg was spliced under the reefer cabinet and then went to the distribution panel. From the distribution panel it went to the battery via the 30 amp fuse.
I rewired all this putting a terminal strip under the reefer and added 10 awg marine to the battery via a 30 amp breaker.
Then I ran 8 awg all the way from under the hood to a separate breaker that feeds the battery. This second line is what I am thinking about using when I need the solar panels further in front of the TM. What my thoughts were is pick up the breaker output to a marine style 2 battery selector switch and switch the breaker between the battery; when towing; to the CC input if I need further extension at the front of the TM. My current portable setup will just reach in front of the tongue. All I would need is the switch, a trolling motor socket and MC4 connectors.

[RottieMom]

Actually, I was looking at a Zamp Portable Solar System and the controller would be on the panels. While I was looking at the pictures on their website I saw a pic that had clamps (just like what comes with Battery tender) and I thought! hey I wonder if I could just clip off those clamps and wire them to a TV side Bargman connector and then just plug the TM Bargman cable in and let the solar panels charge my battery just like I'm doing with Battery tender. BTW, my battery is located in the front of my TM under the sofa. Anyway, if this would work (or makes sense) it sure would be easy to do. I love being able to plug my Bargman into my battery tender with my current setup.

[scrubjaysnest]

For proper solar charging of the batteries the charge controller, CC, must be located as close to the batteries as possible. CC's work by sensing battery voltage and temperature to set their charging rate. If a CC has remote sense and temperature measurement then it doesn't need to be so close to the batteries.

Here are a couple of blogs to review before spending hundereds of dollars on solar.
https://handybobsolar.wordpress.com/ This was has a lot of ranting you will have to dig through.

The golden rules without Handybob's rants
http://www.jackdanmayer.com/rv_elect...Golden%20Rules

The reasons some folks have trouble charging their battery with the reefer on with the TV also apply to CC's mounted on the solar panel; to much volt drop.

Volt drop is the current (amps) squared times the wire Resistance.

The voltage at the battery with the CC at the solar panels 20 feet(bargmen and CC output @ 14.5 volts; typical 100 watt panel Imp = 5.5 amps) from the battery with 5.5 amps is 14.3 volts.

While this will charge the battery it will take much longer and may reduce battery life. To fully charge you will also have to keep the panel in full sun.

With the CC at the battery you will still have the same voltage loss (0.226 volts) but you will be subtracting it from panel Vmp or about 18 volts. This will leave 17.8 volts at the CC input and the CC output will be 14.5 volts

14.5 volts is typical boost or bulk charge voltage desired.

Just my thoughts FWIW

[scrubjaysnest]

To summarize my previous post; the Zamp system will work well the way Cmboyd is thinking of; losses are below 3%(0.281 volts @6.64 amps) which is one of the targets for a solar system. At almost $600 for the 120 watt system, that's two 60 watt panels, one might want to consider the Renorgy 100 watt portable system, two 50 watt panels and separate CC at less then $300. This is available direct, or through either Amazon or Ebay.

Some more math: grp 24 battery

85 AH * 14.5 charging volts * 1/0.77 panel + CC de-rating * 0.05 rate of charge = 80 WH.
This means for a 5% charge rate the 100 watt system or the 120 watt system are a very good match. 5% is a minimum for most batteries.

Two GC-2's
225 AH * 14.5 * 1/0.77 * 0.05 = 211 WH. oooops this is bad not enough solar.

So some over all thoughts, good system for Grp 24's and will most likely let you run a 300 to 400 watt inverter for a couple of hours.

Marginal for Grp 27's and you are likely to be very un happy with GC-2's.

PM me for questions that may not be applicable to this thread.

[RottieMom]

SJN, I hate to say this but I don't know what kind of battery I have. I know I only have one 12v battery, but I haven't opened up the battery box, yet. Sounds like from your post I need to take the kind of battery into consideration with a solar application.