Power Distribution Systems

Mike_H

autos are better - WRWD508
Supporting Member
Joined
Feb 28, 2017
Messages
11,574
Location
Grand Rapids, MI, United States
I'm in the process of a pretty complete refit of my 1978 Class A motorhome. The charger has been replaced with a newer than 1978 charger/converter so at least I'm not boiling my batteries anymore, but it's only able to charge FLA batteries. Since I'm redoing most of the systems anyway, figured I'd start investigating solar, inverter/chargers, Li-Ion Batteries, etc. I need batteries anyway, so it makes sense to me to buy Li-Ion...but how much storage do I need? How do I charge them? I want to eventually be able to add solar...so I want to make sure I future proof for that...etc

I very quickly entered into an area where I don't know what I don't know and need to climb my way up the learning curve. Anyone have experience with this? I know @toximus just bought a new trailer and made sure he could boondock with it...How involved in the specification process were you?

Anyone know of some good resources to boost my learning? Google searches are giving some results, but sifting through the endless blogs from DIY'ers who might know what they're doing is getting old. I've found enough info to know I'll need to sum my expected loads for a 24 hour period, but no one really gets into how to estimate the duty cycle of their DC powered fridge...does it run for 5 hours in a 24 hour period or 20? That will affect my load, obviously. Its all an estimate anyway, so are there rules of thumb to follow? How do I design a system that is easy to add capacity to, as I go along and get a better idea of usage?

So, like most things at the beginning of the learning path, I currently have more questions than I do answers...Any help will be appreciated.
 
  • Like
Reactions: StG58 and rasband
I know @toximus just bought a new trailer and made sure he could boondock with it...How involved in the specification process were you?

I was heavily involved in mine and shipped them many of the parts they installed. However, I was also limited to the brands they'd install.

Right now with 2x 90ah lead-acid batteries, 190 watts of solar, 12v fridge (it is 3-way, but I'd like to save propane), and propane furnace. I'm way more reliant on the generator than I'd like to be or thought I'd be. Thankfully the generator has an autostart and shutoff to charge and it only sips from the massive diesel tank. The batteries make it through the day, but won't get through the night unless I turn off the fridge. I do still need to test for draws to make sure I'm not losing some elsewhere.

My inverter can charge lithium batteries with the flick of a pole switch. But then I'll have to install a DC to DC charger off the truck too. This is my long term plan along with adding another 400 watts of solar which my solar controller can handle (part of where I was involved in the specs).

My short term (quick and dirty) plan is to add another 200ah of lead-acid batteries to double the capacity.

If I had the time and the money to blow on it, I'd bring my trailer to a solar dealer/installer (Victron seems to be the leader) and tell them what I wanted and let them figure it out and install.
 
  • Like
Reactions: Mike_H
I was heavily involved in mine and shipped them many of the parts they installed. However, I was also limited to the brands they'd install.

Right now with 2x 90ah lead-acid batteries, 190 watts of solar, 12v fridge (it is 3-way, but I'd like to save propane), and propane furnace. I'm way more reliant on the generator than I'd like to be or thought I'd be. Thankfully the generator has an autostart and shutoff to charge and it only sips from the massive diesel tank. The batteries make it through the day, but won't get through the night unless I turn off the fridge. I do still need to test for draws to make sure I'm not losing some elsewhere.

My inverter can charge lithium batteries with the flick of a pole switch. But then I'll have to install a DC to DC charger off the truck too. This is my long term plan along with adding another 400 watts of solar which my solar controller can handle (part of where I was involved in the specs).

My short term (quick and dirty) plan is to add another 200ah of lead-acid batteries to double the capacity.

If I had the time and the money to blow on it, I'd bring my trailer to a solar dealer/installer (Victron seems to be the leader) and tell them what I wanted and let them figure it out and install.

Run your fridge on propane, it won’t use much. The furnace is a big user of propane. My last motorhome had a 3 way fridge. I could only use the 12v while driving.
 
Let me sober up, and I've got a lot for you.

Start out by browsing SOK batteries, and Victron systems.

Airstream 27 Globetrotter 27FBQ, 412 amp/hours Lifepo4 batteries, 3.5 to 4 days boondocking / off grid. Going to upgrade to 618 amp/hours. That's almost a full week off grid.
 
  • Like
Reactions: Mike_H
...I'll need to sum my expected loads for a 24 hour period, but no one really gets into how to estimate the duty cycle of their DC powered fridge...does it run for 5 hours in a 24 hour period or 20? That will affect my load, obviously...
You can run an inline meter for a day or two to better estimate your fridge's consumption. I have a "Watt's Up" meter (unfortunately not sold anymore) that monitors all sorts of stats including amps, amp-hours, and peak amps. Loads will vary depending on your fridge's cooling mode, whether or not you pre-cooled the fridge before use, fridge contents, ambient conditions, etc.

If I had to replace my Watt's Up meter today, I'd probably drop a few extra dollars and go with the Powerwerx Watt Meter for $50.99, though cheaper ones are available on Amazon if you desire.
 
You can run an inline meter for a day or two to better estimate your fridge's consumption. I have a "Watt's Up" meter (unfortunately not sold anymore) that monitors all sorts of stats including amps, amp-hours, and peak amps. Loads will vary depending on your fridge's cooling mode, whether or not you pre-cooled the fridge before use, fridge contents, ambient conditions, etc.

If I had to replace my Watt's Up meter today, I'd probably drop a few extra dollars and go with the Powerwerx Watt Meter for $50.99, though cheaper ones are available on Amazon if you desire.

Unfortunately, I won't be able to do that. My coach is already torn apart and I'm putting new appliances in.
 
Have you ordered them yet? Can you do a garage test?

I have a few of my appliances. Still working out what, exactly, I’m going to do. Initially, I started to think about removing propane all together, but now it’s looking like I’ll be able to keep the tank, which is a 60 lb. Along with removing the propane, I was going to do induction cook top and DC compressor fridge. Keeping the tank means I could stay with an absorption fridge (fix the one I have) and use a propane range top vs induction. That reduces my power consumption greatly.

The only large consumer of electric power would be microwave, coffee pot (which I can mitigate with a French press or insulated carafe) and a rooftop AC (which are 13 amp draw at 120v)
 
Whoo-weee...here we go.

It sounds like you have yet to do an energy budget. That's the first thing to do. You can do it on paper or use a spreadsheet. List everything in your motorhome that uses electricity. You don't even have to have purchased everything yet. Manufacturers are really good at providing power consumption figures for RV related stuff. Those power consumption figures may be total BS, but they are happy to provide them. Get both the start up and running power figures. Things like A/C's and refrigerators can suck a lot of amps at startup, and purr along at a lower power consumption level when running.

Figure out how long each item is probably going to run in a day. That's a tough one. Just give it a guess to start out. Multiply amps time estimated hours of run time in a day and that's your daily amp hour power consumption. Multiply that by the number of days between charges desired, and that's your desired / required battery capacity in amp / hours.

Once all the juice is out of the battery, you have to put it back in. Power converters (battery chargers) over 100 amps get really expensive really fast. LiFepo4 batteries have a few charging quirks to be aware of. Issues with temperature and maximum charging rates. As an example - my 206 amp / hour SOK batteries have a maximum charge rate of 50 amps each. I have two right now, so the maximum charge that can be applied is 100 amps. When the third one goes in, then the maximum charge rate would be 150 amps. If the batteries are completely flat, it would take four and a half to five hours to charge at maximum charge rate.

Solar panels and inverters are another kettle of fish to think about.
 
Solar panels have dark secrets that no one talks about. The first is that you are never going to see the rated capacity come out of the panel and go into your battery. Shade, cloud cover, dirt and crud on the panel, orientation to the sun... lots of thing interfere with getting maximum efficiency. On the bright side, in certain circumstances solar panels will keep your batteries topped up and happy.
 
Whoo-weee...here we go.

It sounds like you have yet to do an energy budget. That's the first thing to do. You can do it on paper or use a spreadsheet. List everything in your motorhome that uses electricity. You don't even have to have purchased everything yet. Manufacturers are really good at providing power consumption figures for RV related stuff. Those power consumption figures may be total BS, but they are happy to provide them. Get both the start up and running power figures. Things like A/C's and refrigerators can suck a lot of amps at startup, and purr along at a lower power consumption level when running.

Figure out how long each item is probably going to run in a day. That's a tough one. Just give it a guess to start out. Multiply amps time estimated hours of run time in a day and that's your daily amp hour power consumption. Multiply that by the number of days between charges desired, and that's your desired / required battery capacity in amp / hours.

Once all the juice is out of the battery, you have to put it back in. Power converters (battery chargers) over 100 amps get really expensive really fast. LiFepo4 batteries have a few charging quirks to be aware of. Issues with temperature and maximum charging rates. As an example - my 206 amp / hour SOK batteries have a maximum charge rate of 50 amps each. I have two right now, so the maximum charge that can be applied is 100 amps. When the third one goes in, then the maximum charge rate would be 150 amps. If the batteries are completely flat, it would take four and a half to five hours to charge at maximum charge rate.

Solar panels and inverters are another kettle of fish to think about.

Thanks. Yeah, I have learned I need to do the energy budget. I've started to write down ALL the stuff that runs off electricity. Since I have a motorhome...I have three systems to work on, House AC, House DC, and Vehicle DC. I've found a couple decent, marine centric articles to read on the Victron Site that have been helpful too (as they also have the same three systems).
 
Not directly related to your question but since you have your RV stripped down if you're going to rewire things also these might be helpful. I'm still trying to figure out how to pull cables thru my coach.


RV ENERGY MANAGEMENT SYSTEMS

 
Thanks. Yeah, I have learned I need to do the energy budget. I've started to write down ALL the stuff that runs off electricity. Since I have a motorhome...I have three systems to work on, House AC, House DC, and Vehicle DC. I've found a couple decent, marine centric articles to read on the Victron Site that have been helpful too (as they also have the same three systems).

Victron is really good stuff.

You really don't need to know the exact applience you are going to use to do your budget. All 12 volt refrigerators of a similar size use about the same amount of energy, same with furnaces & etc.

Are you going to do your own wiring?
 
  • Like
Reactions: Wildman
Running A/C and microwave on battery power...can be problematic. It can be done. But it gets expensive really fast.

Yeah, I'm finding that. I'm trying to temper my "what-if" scenarios with what we actually do, 90% of the time. Instant pot and Blackstone are the preferred cooking apparatii. We've used the microwave a few times, but not often. We also camp with some sort of Shore power almost exclusively. So...I'm kinda running dual scenarios in my head...at 6-10 dollars/amp hour for LiFEPO batteries, adding two or three extra 100 Ah batteries to be able to flip the AC on might not be the best use of resources. :)

Victron is really good stuff.

You really don't need to know the exact applience you are going to use to do your budget. All 12 volt refrigerators of a similar size use about the same amount of energy, same with furnaces & etc.

Are you going to do your own wiring?

100%, without a doubt. Just like the Jeep, I find that I care about my own stuff far more than someone who I'm am paying to complete a job does. I do probably need to buy a new battery lug crimper. The hydraulic one I have from Amazon seems to overcrimp.
 
  • Like
Reactions: Wildman and StG58
Not directly related to your question but since you have your RV stripped down if you're going to rewire things also these might be helpful. I'm still trying to figure out how to pull cables thru my coach.


RV ENERGY MANAGEMENT SYSTEMS


Thanks. I bought a surge protector for shore power a while ago...its not installed, but I do have one! Its a progressive Dynamics model, IIRC. Its a lot easier to run wires in the coach when you don't have any finished walls!

1681758830539.png
 
I'd just come across those panels from Intelitonx recently. Not sure how good they really are.


I'll second the recommendation for Victron. I'm a little pissed that the RV shop hadn't used them in mine when I was having the roof replaced.

Those A/C units you bought don't require as much power as older units. You're going through all the thoughts I've been having on mine. And trying to balance want/need is hard.
 
  • Like
Reactions: Mike_H
I'd just come across those panels from Intelitonx recently. Not sure how good they really are.


I'll second the recommendation for Victron. I'm a little pissed that the RV shop hadn't used them in mine when I was having the roof replaced.

Those A/C units you bought don't require as much power as older units. You're going through all the thoughts I've been having on mine. And trying to balance want/need is hard.
Now is the time for me to install a good system. I have the access and I need batteries, anyway. Looking at a few of the cost comparisons of AGM vs LiFePO, it’s silly to not install lithium, if you can swing the up front cost. Even that isn’t terrible now, I’m seeing quite a few brands (Epoch, kilovault, SOK) coming in around 600 bucks for a 12V, 100’ish Ah battery.

I’m going to get the system set up for future expansion into solar, but I don’t have any plans to do that yet. So…design leaving room for the solar controller and making sure the inverter/charger has an input for it.

I’m also looking to get a DC/DC charger to run off the engine alternator. My running electrical load isn’t all that high (carbureted engine, no pcm) so I have quite a bit of overhead on the 100 amp alternator installed too.
 
  • Like
Reactions: Wildman