For the first part of this article, click here
In the last installment we identified some of the potential problems in an RV campers 12V systems. These include
- Inadequate converters for rapid charging (often low end, 2 stage)
- Inadequate cabling (length and gauge) – causing voltage drop and severely impacting charging.
For reference my installation is in a Starcraft Autumn Ridge 246RKS with the following related items
- Rear kitchen – which is where the converter is
- IOTA 2 stage voltage converter
- 2 x Group 24 Interstate marine batteries on the tongue.
- 8AWG cable between the converter and the batteries – likely over 20′ long
Notice the rear converter and front batteries
Here is the converter - all alone in the rear of the trailer
If you remember, I strongly considered just upgrading the wiring between the converter and the batteries. However running some numbers over at NoOutage’s voltage drop calculator it became very clear that this wasn’t going to work over the 20′ plus distance I had to run the wire. Even with 1/0AWG wire the drop was .5% and that stuff is just too darn hard to work with in the confined space and routing required in a typical RV/Camper. Like most RV/Campers, the AC and DC power distribution are located with the converter. That meant that the AC power came in from the outside plug to this location for it’s circuit breakers and distribution. Typically you will find that the converter has it’s own circuit breaker on the AC power breaker panel. The first action I took was to move the converter to the front of the trailer. Off to HomeDepot to pick up the following:
- 30′ of bulk 10/2 AC wire, very similar to this. Not the exact wire, but gives you the idea
- 30′ of bulk 6 AWG insulated wire
- 15′ of bulk 4 AWG insulated wire
- 5′ of flexable conduit similar to this stuff
- An electrical junction box like this one
- Misc bits like terminal lugs, wire nuts, grommets, etc
There were a couple of challenges in finding parts. The biggest for me was finding a fuse and fuse holder that could handle the 4AWG wire. I wanted the fuse as close as possible to the batteries so wanted an inline solution. Eventually I discovered the high end audio folks out there. They use a lot of this high gauge wire for similar reason and that is where I found the StreetWires Fuse Holder. Once I had that it was not hard to find fuses and power distribution blocks.
The intention is to run the 120V AC from the output of the converter breaker from the power distribution panel to the front storage compartment of the trailer. I also replaced the 8AWG from the batteries with 6AWG – dramatically decreasing the voltage drop when running the DC systems. The DC part might could have been skipped, but I figured – as long as I’m there doing this…. In my new converter location, the distance “as the cable runs” was about 5 feet. With the goal of getting the fastest charge on the batteries I wanted to absolutely maximize the amount of voltage from the converter to the batteries. After spending some more time over at NoOutage’s Voltage Drop Calc I decided to go with the 4AWG wire from the converter to the batteries.
I had a 2 stage converter that did a slow charge with 13.6 volts, I knew I wanted to bump it up to a 3 stage to decrease the charging time down the road. With a 3 stage converter, pushing 22 amps, even over that short 5 foot cable run I have a 0.4% voltage drop. While higher than I wanted, the degree of difficulty working with bigger wire lead me to 4AWG. Even at this, it was difficult to get the wire through the conduit and into place. So, the old 8AWG wire was run under the trailer inside the frame along the street side of the trailer. I used the same routing to bring both the 10/2 and 6AWG from the power distribution panel in the rear to the front. I drilled a hole in the floor of the trailer to bring all of the wiring to the front storage compartment where the converter is now located. In the storage compartment I used the conduit and junction box to protect the wire from me loading and unloading “things” in the compartment. The largest challenge of the cabling job was fitting all of the wire through the conduit. I knew there was a reason I don’t run cable for a living! With 2 of the 4AWG and the 1 run of the 10/2 AC going through the conduit it was quite difficult to do without damaging the insulation on the cables. I have to admit, there are nicks in the insulation, but noting that went all the way through so I’m good with it.
This is just inside the street side front storage compartment door and is bolted to the front of the trailer.
Conduit that goes from the converter, and through the floor.
Here you can see where the new penetration is through the floor of the front storage compartment.
This is the back end of the trailer where the existing penetration for wires is. Yellow wire is the 10/2 AC and the black is the 6AWG.
Another challenge was terminating the lugs on the 4AWG cable. I didn’t want a “hack” crimp on this so played around a bit. I tried a “chain link fence” crimper from the hardware store, but ended up returning it as I didn’t feel it had the right size die for the job – crimp seemed loose even though I couldn’t pull out the cable with my hands. I got lucky, my work was in occasional need of a cable crimper to terminate 6AWG wires – and I needed the 4AWG crimps – yet neither of us wanted to spend the hundreds of dollars that quality crimpers of this type can cost. I did some digging and found this Harbor Freight hydrolic one with interchangeable bits. From my one time use, and works occasional use, it will work out – – plus they paid for it! (it was $50 in Jan 2012 when I bought it)
I have all this set up – with the original 2 stage charger – and it works! When in charge mode, I measured the full 13.6V DC at the batteries!
However, there was still a problem in that my batteries seemed to run down WAY too fast. I unhooked the cables from the batteries and they both measured around 12.7V DC which is a full charge. So off to Pep-Boys to pick up a Hydrometer. I tested every cell in my 2 Interstate 12V SRM-24 Marine batteries – and low and behold, one of the cells didn’t register at all on the Hydrometer! Bingo – I’ve got a dead cell in one of my batteries.
I knew from my prior reading at the Wind&Sun Forums and The 12V Side of Life that mixing old and new batteries was a bad idea, meaning I had to replace them both. I took some measurements of the space on the tongue where they batteries sit and started searching. The criteria I wanted were:
- True Deep Cell Batteries
- Maximum number of A/H’s
- Had to fit in the existing space on the tongue
I really don’t think it matters if the batteries are 12V or 6V – just that they are true deep cycle. I was looking for the maximum number of A/H’s I could fit in the space.
When selecting batteries, if you choose 12V you get to add the AH capacity of each battery together. If you select 6V then, with 2 batteries, you get the AH capacity of one of them. IE: 2x115AH 12V gives you 230AH usable 12V power whereas 2x215AH 6V batteries gives you 215AH of usable 12V power.
Remember: If you change from 12V to 6V it requires changing the way the batteries are hooked together. Hooking up 6V batteries like your 12V’s were would underpower everything. Hooking up 12V’s like 6V’s should be would give you 24V’s and likely burn up equipment on your camper!!!
I believe that true deep cell batteries are important in RV applications. Marine batteries like I had before are a compromise – they are designed to have some deep cell performance, but also provide starting level amperage for starting your boats engine. That translates to thinner plates in the battery and less tolerance to deep discharges that you may encounter in your boondock camping. Using deep cell batteries to start an engine may work, but it will be VERY hard on the battery. Same is true using starting batteries in a slow/deep discharge like happens in camping.
I really like the Trojan T105’s
– raving reviews all over Wind&Sun as well as all the RV forums. They met all my criteria above and would be fantastic. However, I couldn’t find them for less than $140 each locally. Another, more cost effective option, that also recieves good reviews are the Golf Cart batteries from Sams Club and Costco. While I prefer Costco, the guy at my local store said they don’t stock them yet – and didn’t know when they would. Sams had them in stock and they were branded as Energizer. Interestingly, right now their website now lists an identically spec’d Duracell
. Key specs for me were:
- 215: 20 AH Rate
- Standard GC2 size (10 3/8 x 7 1/8 x 10 7/8) means it will fit
- True deep cycle – no cold cranking specification
- Cost – $80 each.
Picked two off the shelf that had very recent manufacturing dates (same month I was buying) and hauled them home. Installed them in series (vs the in parallel that the 12V’s were) and we were off to the races!
Here they are - they fit in my existing battery boxes. I'm not real happy with the fuse install so will likely move it/figure something else out.
As mentioned before, I typically boondock. I want my generator to run as little as possible to get my batteries back up to a good charge. A two stage converter like my Iota would still take many hours to bring the batteries up. There seem to be 2 converters that have a big following in this department:
The prior owner of my previous trailer, a Casita Spirit Deluxe 17′, had replaced its stock converter with a Progressive Dynamics and it worked great for me. So I choose the PD9245C. I purchased from BestConverter.com whom threw in the PD92201 Remote Pendant for free! Because when not in use, I leave the trailer plugged into a 30A plug on the side of my house, one of the things I really like about this converter is it’s Desulfication Mode. After the batteries are fully charged the system goes into Storage mode – holding 13.2 volts on the batteries. This will hold a full charge on the batteries, without gassing or causing water loss. The problem with this is that over time, the acid and water will separate in the battery, and that will cause stratification on the plates of the battery leading to loss of power. To fight this, every 21 hours the Progessive Dynamics converter jumps up to boost mode (14.4V) for 15 minutes. This causes slight gassing in the batteries (bubbles) which stir up the electrolyte and extends their life.
This is the permanent 30A outlet I had installed on near the trailer storage location on the side of my house.
At this point I’ve already done the hard part of moving the converter and installing the new one was a piece of cake. 10/2 120V AC in – 4AWG 12V DC out. Done.
I’m a firm believer for a boondocker – and it can be done for a lot less than you may think! Here is why. My camper had the same bulbs throughout, T10 wedge type – I think they were the model 194’s. These are the 13W bulb. Ohms Law tells us that 13W / 12V = 1.08 Amps. Most of the fixtures have 2 of these, doubling the amp draw. You can see that just having a few lights on for a few hours can drain down my 215AH capacity of batteries. 3 lamps @ 2A each times 4 hours = 24AH – just for lights!
LED’s of similar brightness pull about 1/10 that much!! Meaning I can run 10 LED’s for the power consumption of 1 incandescent! Sounds like a winner to me so I replaced all my bulbs with LED’s. I’ll have a post soon on this little project.
I’m a happy camper! When the batteries are fully charged, and I force the converter to boost mode via the pendant – I measure 14.36V DC at the batteries themselves and can see them gassing (bubbling). If the batteries are run down to say 60%, and the converter is in boost mode, I measured 13.12 – but that is normal. Those batteries are likely taking in 20A at this point and charging up very quickly and safely.
Last weekend I had our first real test of this setup. We did a three night trip out into the Lincoln National Forrest. Perfect weather and a great trip!
I used the following electrical loads:
- Lights – as they are LED we didn’t try to conserve and used them a lot. Porch light was on most of the night and inside as desired.
- Heater – It got cold at night – as low as 25F! Set the furnace at 70F and just let it run as needed. This was by far the biggest load on the batteries.
- Water – pumped about 70 gallons over the weekend from the fresh tank.
- Other – Fridge, detectors, radio, slide, etc. Used them all as desired.
We never hooked up the generator (although our friends had to on their trailers – I see a project helping them in the future!) On the 4th day, I took a voltage reading from the batteries right before hooking up to come home. 12.31V DC. I had about 70% of my batteries left after using everything we wanted/needed for 4 days and 3 nights. Awesome!
Stolen from The 12V Side of Life
Remember, you typically don’t want to run them down below 50% to get a good long life from the batteries. 50% is when you measure 12V DC with a volt meter. Meaning I had only used about 1/2 of what I could have before wanting/needing to recharge!
During the summer we rarely need the furnace so I bet we could go well over a week in the boonies. I just can’t say how pleased I am with the results.
A HUGE thank you to all my sources (linked throughout this writeup) Without them, and their knowledgable members I couldn’t have pulled this off. How did we survive before the internet?????
I hope some of you find this helpful – let me know if you have any questions!
Some, but not all, of the sources I used to learn this: