Thinking about installing the Renogy 20 amp DC to DC charger

[Rob Culver]

Hello all,
Just got back from a long trip in which I turned off the Trailmanor Dometic Fridge to avoid the large DC amperage draw, (more than 12 amps), it draws on the Lithium Lifepo4 battery I installed. The tow vehicle doesn't usually supply more than 6 or 7 amps when driving either. Without power for several hours at a time, that made the fridge somewhat unusable on hot long driving days.

I'm considering installing the Renogy 20 amp DC to DC charger referred to in other threads on this forum but only if it's safe, easy, and doesn't require running new heavier gauge wires on either my Tow vehicle or the TM.

When looking at this TM electrical diagram here: https://www.trailmanorowners.com/for...8&d=1584889354 you see a 30 amp fuse between the TM battery and the converter. Is installation as straight forward as hooking up the Renogy 12 volt input and output between that 30 amp fuse and the +12v on my Lithium battery? And then putting the input and output grounds to the battery negative terminal?

Reading through the Renogy installation guide starting at page 7 of this url, https://www.renogy.com/content/RNG-D...060-Manual.pdf, that appears to be possible. The only catch is that they refer to a D+ ignition wire plug on the Renogy that needs to be connected from the tow vehicle ignition in order to turn on the Renogy only when the Tow vehicle is running. I would think it would be Ok to hook that D+ connector up to something so it would always be "On" because there is no power to the 7 pin bargeman connector from the tow vehicle and thus no power to the Renogy input side in any case unless the Tow vehicle is running. I've tested that.

Just interested in anyone's thoughts who might have already installed the Renogy 20 amp DC to DC charger and if they were able to do it without running any new cables anywhere other than just the new short cables to attach it to the TM battery. Thanks in advance for anyone's thoughts on this!

[Bill]

I'm not sure this will work out.

Why not? As you know, in order to charge a battery, you have to apply a higher voltage to it than its fully-charged voltage. Recall that as you are driving down the road, the truck battery is already fully charged, and it is the truck battery that controls the alternator voltage. Therefore, the alternator is producing only enough voltage to maintain the truck battery, but not enough to charge it. So when the truck battery is connected to the TM battery, the TM battery won't get charged either. You need to boost the voltage at the TM end, high enough to charge the TM battery. And that is what the Renogy does. All good so far.

Next? The wire that runs from the alternator, and down the length of the truck and the TM, has resistance. And as the charge current runs through that wire and through that resistance, there is a voltage drop in the wire. This means that the voltage that arrives at the TM battery is even lower than the voltage at the truck battery. It needs to be boosted even more, and again, the Renogy can do that. Still good.

The problem? In order for the Renogy to produce 20 amps at its output, it has to take in more than 20 amps at its input. As an example, to produce 20 amps output, perhaps it needs to take in 30 amps at its input. And the wire down through the truck may not be capable of carrying 30 amps. Now you are facing the need to replace the existing wire with a heavier one.

The exact numbers depend on the size of the existing wire through the truck and the TM, and its length, and the number of connectors in it (connectors have a bit of extra resistance). They also depend on the efficiency of the Renogy charger. So I can't tell you what you will have to do. But I know that many years ago, I had to rewire my Ford Explorer to reduce the voltage drop. I had to run a new wire all the way from the truck's alternator to the 7-pin Bargman connector on the rear bumper.

In those days, DC-DC chargers were not available, so even with the new wire, it didn't work very well. But it helped. Today, with the DC-DC charger, it should do what you want - but I think you may need to upgrade the wire size to something that will carry the needed current.

I'm not the expert here, so I am waiting for one of them to chime in. In the meantime, if the above comments aren't clear, please ask questions.

Bill

[Rob Culver]

Originally Posted by Bill

I'm not sure this will work out.


I'm not the expert here, so I am waiting for one of them to chime in. In the meantime, if the above comments aren't clear, please ask questions.

Bill

Thanks Bill. I'd settle for a 15 amp charger if that kept the amperage much lower than 30 through the tow vehicle. I think I may try and measure the total number of Ohms resistance between my vehicle battery and the 12 volt pin on the connector too although that won't be easy. But it would give me an idea of how much of a voltage drop through the wiring is occurring.

[ShrimpBurrito]

Originally Posted by Rob Culver

Just interested in anyone's thoughts who might have already installed the Renogy 20 amp DC to DC charger and if they were able to do it without running any new cables anywhere other than just the new short cables to attach it to the TM battery. Thanks in advance for anyone's thoughts on this!

I have installed a 20 amp DC-DC charger, but not one by Renogy. And my TV tow circuit was rated for 30 amps. I just connected the charger's input leads to the wires in the TM that come from the TV charging circuit. See this thread:

https://www.trailmanorowners.com/for...ad.php?t=10587

So, as Bill said, it will draw as much as it needs, but then provide sufficiently high voltage to charge the batteries, regardless of what the input voltage is.

The unit is still installed and works like a champ. I haven't had to do anything do it in the last 14 years other than reconfigure it to charge lithium batteries. Dang, cannot believe that was 14 years ago.....

Dave

[Wavery]

Originally Posted by Rob Culver

Just interested in anyone's thoughts who might have already installed the Renogy 20 amp DC to DC charger and if they were able to do it without running any new cables anywhere other than just the new short cables to attach it to the TM battery. Thanks in advance for anyone's thoughts on this!

Hi Rob,

Have you given any thought to adding solar to your trailer? ~400W of solar may alleviate the need for a DC to DC charger. Depending on your battery capacity. Just a thought......

[ShrimpBurrito]

Originally Posted by Wavery

Hi Rob,

Have you given any thought to adding solar to your trailer? ~400W of solar may alleviate the need for a DC to DC charger. Depending on your battery capacity. Just a thought......

An excellent suggestion. Even 300 watts might be enough, and you can easily get that many panels on the rear roof. With even a 50% yield (150 watts), you'd have enough to run the fridge and have a bit left over. And then when you get to camp, any discharge from the fridge will very likely be overcome by solar charging at camp.

Dave

[Rob Culver]

Originally Posted by ShrimpBurrito

An excellent suggestion. Even 300 watts might be enough, and you can easily get that many panels on the rear roof. With even a 50% yield (150 watts), you'd have enough to run the fridge and have a bit left over. And then when you get to camp, any discharge from the fridge will very likely be overcome by solar charging at camp.

Dave

Thanks Dave and Wavery. Solar's another option which I've considered. The solar has it's limitations in that it barely works without direct sunlight but if there's not direct sunlight then the refrigerator doesn't need to work nearly as hard either.

Right now I have 100 watts on the rear roof but I'm thinking the solar panels on it could be damaged because I've never seen it supply more than 1.8 amps even when the sun is directly over head. So that would be no more than 20 to 25 watts. This is a low profile panel which came from the TM factory. I've been told that the low profile panels don't work as well as the raised panels but not sure on that. But they are nice in every other way as far as being low weight and low profile to the wind.
Is there a particular brand of panel you would recommend to get the 200 to 300 watts? Thanks in advance!

[ShrimpBurrito]

A 100W panel should be generating far more than 25 watts in direct sunlight. I consistently get 260-280 watts out of my 300W array in direct sunlight, both in the northeast and southwest, and even on a few occasions, it has been slightly over 300 watts.

And during a torrential rainstorm this summer, I still got ~25-30 watts, though granted, my three 100W panels are wired in series, and so they generate a higher voltage than if wired in parallel. That enables them to generate at least some power during low light conditions, when otherwise the controller would not seen enough voltage to even do any charging.

I bought rigid panels with Sunpower cells in them, which have a higher rated efficiency, but I don't see that those specific ones are sold anymore. I'm wondering how much extra power a bifacial panel would give you when mounted on a TM roof. Some of these panels now have 16 busbars, which improves efficiency. At first glance, this one looks pretty good:

BougeRV 24V N-Type 16BB 100W Bifacial Solar Panel, 24V 100 Watt Solar Panel
https://www.amazon.com/BougeRV-N-Typ.../dp/B0CSSLYXDK

...and on sale now for ~$104.

And then pair them with a Victron MPPT controller.

Wayne will chime in with his thoughts I'm sure.

Dave

[Wavery]

Rob,

I buy a lot of solar panels off craigslist. I've never gotten a bad one. Here's a 375W panel that should fit nicely on the rear shell of your TM. It's 78" x 40".

If I got it right, you live in Orange County.

Do a search on CL for "solar panels". There's a ton of them, even brand new ones for around $0.50 per watt. I found mine ( in Menefee (brand new) for $0.45 per watt and they are bifacial.

The 1st thing that you need to consider is your battery storage. That's where it starts getting costly. A 280ah LiFeP04 battery will cost you around $550 (with coupon). Then you need an MPPT solar controller and misc hardware..... ~ $150-$200.



https://orangecounty.craigslist.org/...767753654.html

https://www.amazon.com/CHINS-LiFePO4...1zcF9hdGY&th=1

https://www.amazon.com/Victron-Smart...s%2C170&sr=8-2

[Rob Culver]

Originally Posted by Wavery

Rob,

I buy a lot of solar panels off craigslist. I've never gotten a bad one. Here's a 375W panel that should fit nicely on the rear shell of your TM. It's 78" x 40".

If I got it right, you live in Orange County.

Do a search on CL for "solar panels". There's a ton of them, even brand new ones for around $0.50 per watt. I found mine ( in Menefee (brand new) for $0.45 per watt and they are bifacial.

The 1st thing that you need to consider is your battery storage. That's where it starts getting costly. A 280ah LiFeP04 battery will cost you around $550 (with coupon). Then you need an MPPT solar controller and misc hardware..... ~ $150-$200.



https://orangecounty.craigslist.org/...767753654.html

https://www.amazon.com/CHINS-LiFePO4...1zcF9hdGY&th=1

https://www.amazon.com/Victron-Smart...s%2C170&sr=8-2

Thanks Wayne for the excellent suggestions! I actually live in north county San Diego.

I already have a 200 AH lifepo4 battery. Works great. I also have a bluetti AC180 100 AH portable but that's beside the point.

I uploaded a few pictures of what I've got as far as the solar goes. I have a 30 amp GoPower PWM solar controller installed near the kitchen sink. The picture shows it set to AGM but I changed that to lithium. Do I really need to change that out if I stay under 300 watts as 30 x 12 = 360 watts.

If it is worthwhile to change it out, is it a simple matter of unscrewing the existing controller and drop in replacing it with the MMTP one?

Looking at my existing roof top solar connections, would you say that the new panels you recommend would have no trouble plugging in to those connectors?