I'm Greedy... Fastest Charge Controller? [ANSWER: Victron]

DeanP · October 2019

@Newbomb_Turk I just finished a very similar project on our 2020 T@B 400. I understand your desire to reduce the voltage drop as much as possible, but here's what I did and I'm really happy with the results (albeit with only a half a dozen uses). I went with the MPPT 75/15, 30 ft of 10ga wire and two 100 watt monocrystalline panels. I'm pretty sure the wiring off the Zamp connector inside the trailer is 10ga as well. It was a fairly simple project, has more flexibility in terms of panel placement than a roof mounted system, works great and was completed for about $325.

I'm pretty sure the 75/15 will only take up to 10ga wire. So, if you're really set on using 8ga wire, you'll have to trim some strands to make it fit. Not worth the effort in my book.

Victron MPPT 75/15:

https://www.amazon.com/Victron-BlueSolar-MPPT-Charge-Controller/dp/B00U3MK0CI/ref=sr_1_4?keywords=charge+controllers+for+solar+panels+victron&qid=1570830331&sr=8-4

100 Watt Monocrystalline Panel X 2:

https://www.amazon.com/Newpowa-Polycrystalline-Efficiency-Module-Marine/dp/B0725RZ22H/ref=sr_1_1_sspa?crid=3DIJ2J8RPET4Q&keywords=solar%2Bpanel&qid=1570830065&sprefix=solar%2Bpa%2Caps%2C176&sr=8-1-spons&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExUEtGSTJSSFpLWVNGJmVuY3J5cHRlZElkPUEwOTkyOTIxMlVHVlBMTFNCWlhOWCZlbmNyeXB0ZWRBZElkPUEwMjc5MTA4WlhDTVdINU8wSFNTJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ&th=1

Solar extension cable:

https://www.amazon.com/BougeRV-Extension-Female-Connector-Adaptor/dp/B07BRFPD6R/ref=sr_1_4?crid=1GVFEUMSIM8PR&keywords=solar%2Bextension%2Bcable&qid=1570830429&sprefix=solar%2Bextension%2Caps%2C155&sr=8-4&th=1

rfuss928 · October 2019

Basic electrical engineering will show your 5% goal unrealistically optimistic.

For example:

100 feet of #10 copper wire is 0.100ohm, #8 is 0.063

If you have 100 watt panels at full power (very rare occurance) the maximum possible current is about 6 amps at close to 17 volts.

The power lost in the 100 feet of wire (50 foot pair) is 3.6 watts in the #10 wire and 2.3 watts in the #8 wire. (Watts = amps squared times resistance)

About 1 watt difference in losses at 100 watts (1%) full power.

When bulk charging is complete, the current at absorption and float stages will be about 1 amp or less and losses in power and voltage will become insignificant.

IMO the obsession with large gauge wiring is unjustified when the overall system performance and efficiency are properly considered.

Cbusguy · October 2019

There ya go a lot of really solid answers.

I purchased a 50 foot 10 Gage extension cord and cut the ends off it and that is what I use for chasing the sun.

If you are worried about voltage drop....wire your panel in series and get your voltage higher and it will help reduce the loss in longer wire runs.

What ever controler you purchase make sure it is designed to do it and should probably have at least a 40 volt input voltage.

DougH · October 2019

My AWG 10 solar cables wouldn't come close to fitting. Very small wire crimp basket. I'm not a EE, but cutting away some wires to go from 10 AWG down to 14 AWG for just a quarter inch shouldn't make any measurable difference right?

falcon1970 · October 2019

@DougH
Seems to me it would be like putting a big resistor in the line. Essentially you will have taken the part of the 10 gauge wire that you cut out completely out of the circuit--leaving you with, essentially, a 14 gauge circuit.

DougH · October 2019

Now have a 3rd matching ETFE 2.0 BougeRV panel, so all three flex panels finally match. With the back of the T@B facing West with panels inclined at around 50 degrees off horizon, and at 1:30pm with the sun at 45 degrees off horizon (due South), I'm already seeing 175W and 13A to the battery bank. Happy with new Victron controller.

LATEST (2020): In North Texas with light cirrus clouds around peak sun, up to 200W in weak January sun. At high altitude in clear armosphere have not exceeded 240W yet. Victron 100/20 with max charge rate set to 18A.

Panels:  https://www.amazon.com/dp/B07C94TPLT
Controller:  https://www.amazon.com/dp/B075NPQHQK
Batteries:  https://www.amazon.com/dp/B004DR3IIC
Inverter:  https://www.amazon.com/dp/B07CKBJ9KP
Monitor:  https://www.amazon.com/dp/B07B4CWKRJ
------------------------
Total: ~$1500

jkjenn · October 2019

Awesome!

rfuss928 · October 2019

DougH said:I'm already seeing 175W and 13A to the battery bank. Happy.

Good info and encouraging results from your set-up.

Just FYI and a point of comparison;

If you calculate the watts to the battery, the result is 171 watts. A loss of 4 watts(~2.5%) of panel output in the controllers DC to DC conversion.

In the example in my earlier post about wire gauge choices, changing from 8 to 10 gauge for 100 feet of wiring made only a 1% difference at 50% higher panel current. This would be ~0.6% wiring loss difference in these conditions.

A good illustration showing wiring losses are generally insignificant in the overall performance of these small portable PV systems.

DougH · October 2019

@rfuss928 : Is that more efficient than other brands? Because I've noticed the heat fins on the Victron 100/20 don't even get warm...

jkjenn · October 2019

rfuss928 said:

DougH said:I'm already seeing 175W and 13A to the battery bank. Happy.

Good info and encouraging results from your set-up.
Just FYI and a point of comparison;
If you calculate the watts to the battery, the result is 171 watts. A loss of 4 watts(~2.5%) of panel output in the controllers DC to DC conversion.
In the example in my earlier post about wire gauge choices, changing from 8 to 10 gauge for 100 feet of wiring made only a 1% difference at 50% higher panel current. This would be ~0.6% wiring loss difference in these conditions.
A good illustration showing wiring losses are generally insignificant in the overall performance of these small portable PV systems.

I used 8# wire in my first setup. What a pain to work with!! Too unwieldy and the gains aren't worth the pain.

rfuss928 · October 2019

DougH

4 watts isn't much - think night light bulb.

I don't know about other brands. Very few have as much data so readily available to the user as the Victron products.

I know the MorningStar MPPT controllers have much larger heat sinks than Victron on comparable capacity units. That might imply more heat (waste energy) to dissipate therefore lower efficiency.

On the other hand 2.5% is a small loss to a device that yields 10-20% system efficiency gains by optimizing panel output and matching battery SOC requirements.

DougH · October 2019

I no longer needed the old Epever solar controller's MT50 remote display next to the inverter switch and battery monitor display (since the new Victron just uses Bluetooth).

A woodworking shop near me has baltic birch that matches the T@B cabinet color and pattern pretty well when oiled or varnished, so today I added a couple cell phone / knick-knack shelves. They only come out 5.5" from the side wall, are screwed and glued into the side and rear T@B wood elements, and aren't in the way when sitting or sleeping. I stuck the inverter switch and battery display in a box on the front of the passenger side of the new storage addition.

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I'm Greedy... Fastest Charge Controller? [ANSWER: Victron]

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