24 Volt Wiring Diagram Review and Questions

[willystyle]

Hey everyone,

Some background... I have pretty limited experience with electrical work.

I travel the country doing contracts for the US Forest Service. To reduce fuel costs I try to get my 5th wheel (2021 Grand Design Momentum 397th) as close to job sites as possible. This often means long-term boondocking without any shore power for 80% of the year. For now we use a generator for most of our power needs. My goal is to eventually put ~2000 watts of solar on the roof to supplement our power supply. For now however, I'll be installing everything but the panels and associated wiring.

Questions,

I have an onboard onan generator which needs 12v and ~350 cca to start. Since I'm going 24 volts I think I'll have to keep the current 12v interstate I have installed and use a 24-12 DC-DC charger (victron) is this the only route I can take? what would the advantages/disadvantages of this method vs. a 110v trickle charger. can I use the stock converter charger? Haven't determined wire or fuse size for that yet.

Is my single 200ah 24v battery enough to power this system for a month or 2 before I order the other 3?

I've sized the wires extra large as a safety precaution and as I add to the system/modify it I don't want to worry about it. Are there negatives other than cost/workability when looking at wire size?

I have a Lippert One Control system that I assume runs on 12VDC. I'm wondering if anyone has any experience wiring that system into a 24 volt bank. Any tips? what to look out for?

If y'all could please take a look at my diagram and give me some advice on improvements I could make and any errors there may be.

[A.Texas.Yankee]

Hey everyone,

Some background... I have pretty limited experience with electrical work.

I travel the country doing contracts for the US Forest Service. To reduce fuel costs I try to get my 5th wheel (2021 Grand Design Momentum 397th) as close to job sites as possible. This often means long-term boondocking without any shore power for 80% of the year. For now we use a generator for most of our power needs. My goal is to eventually put ~2000 watts of solar on the roof to supplement our power supply. For now however, I'll be installing everything but the panels and associated wiring.

Questions,

I have an onboard onan generator which needs 12v and ~350 cca to start. Since I'm going 24 volts I think I'll have to keep the current 12v interstate I have installed and use a 24-12 DC-DC charger (victron) is this the only route I can take? what would the advantages/disadvantages of this method vs. a 110v trickle charger. can I use the stock converter charger? Haven't determined wire or fuse size for that yet.

Is my single 200ah 24v battery enough to power this system for a month or 2 before I order the other 3?

I've sized the wires extra large as a safety precaution and as I add to the system/modify it I don't want to worry about it. Are there negatives other than cost/workability when looking at wire size?

I have a Lippert One Control system that I assume runs on 12VDC. I'm wondering if anyone has any experience wiring that system into a 24 volt bank. Any tips? what to look out for?

If y'all could please take a look at my diagram and give me some advice on improvements I could make and any errors there may be.

I didn't see you mention inverters so that leads me to ask why are you going to a 24v system? Never mind, on your diagram it's there...

Don't touch your 12v side of things. Maybe remove your inverter/charger from the factory. Use a DC to DC converter like the Orion you referenced. Keep 24v and 12v separate except for the 24v to 12v converter. This is not thr only way to do it, but unless you just don't want a 12v battery, it's the easiest.

As far as "enough power" that is not an easy question to answer. You'll need to calculate drain vs capacity to see how long it will last you. You'll be running the generator the same amount, really, because you'll have to recharge the batteries until you get solar.

[willystyle]

I'm going with a 24v system to have less batteries on board. My goal is a ~20kW system which would be 4 200ah 24v batteries vs. many more 12 volt.

[A.Texas.Yankee]

I've sized the wires extra large as a safety precaution and as I add to the system/modify it I don't want to worry about it. Are there negatives other than cost/workability when looking at wire size?

I have a Lippert One Control system that I assume runs on 12VDC. I'm wondering if anyone has any experience wiring that system into a 24 volt bank. Any tips? what to look out for?

If y'all could please take a look at my diagram and give me some advice on improvements I could make and any errors there may be.

Extra large is just more money. You may run into compatibility with terminals, and it may be harder to manipulate.

See my comment about leaving 12v system alone and separate and you won't have to touch the One Control (not possible to switch that to 24v anyhow)

[A.Texas.Yankee]

I'm going with a 24v system to have less batteries on board. My goal is a ~20kW system which would be 4 200ah 24v batteries vs. many more 12 volt.

Going 24v over 12v won't necessarily reduce the amount of battery space and weight. Capacity doesn't really change between 12v and 24v. 24v is more efficient and less amps, as the main benefit.

[willystyle]

Well the efficiency and less amperage is also important to me to bring down the costs of the solar MPPT. I'm pretty set on 24v.

Does the one control system draw all of its power through the 12v distribution panel? Didn't see a fuse labeled for it and haven't gone digging to trace wires.

...also was unable to find any wiring diagrams floating around the internet.

A big concern is being able have full functionality of the interior touchscreen control panel. Including starting the generator.

I'm fine with having a 12v battery to turn-over the generator and a 24v bank to run everything else.

[Canyonlight]

@willystyle - David @SolarPoweredRV has a 24V system is pretty knowledgeable about this. Possibly David will chime in or you may want to PM him.

Thanks, in advance David !

Dan

[SolarPoweredRV]

Hey everyone,

Some background... I have pretty limited experience with electrical work.

I travel the country doing contracts for the US Forest Service. To reduce fuel costs I try to get my 5th wheel (2021 Grand Design Momentum 397th) as close to job sites as possible. This often means long-term boondocking without any shore power for 80% of the year. For now we use a generator for most of our power needs. My goal is to eventually put ~2000 watts of solar on the roof to supplement our power supply. For now however, I'll be installing everything but the panels and associated wiring.

Questions,

I have an onboard onan generator which needs 12v and ~350 cca to start. Since I'm going 24 volts I think I'll have to keep the current 12v interstate I have installed and use a 24-12 DC-DC charger (victron) is this the only route I can take? what would the advantages/disadvantages of this method vs. a 110v trickle charger. can I use the stock converter charger? Haven't determined wire or fuse size for that yet.

Is my single 200ah 24v battery enough to power this system for a month or 2 before I order the other 3?

I've sized the wires extra large as a safety precaution and as I add to the system/modify it I don't want to worry about it. Are there negatives other than cost/workability when looking at wire size?

I have a Lippert One Control system that I assume runs on 12VDC. I'm wondering if anyone has any experience wiring that system into a 24 volt bank. Any tips? what to look out for?

If y'all could please take a look at my diagram and give me some advice on improvements I could make and any errors there may be.

@willystyle - David @SolarPoweredRV has a 24V system is pretty knowledgeable about this. Possibly David will chime in or you may want to PM him.

Thanks, in advance David !

Dan

Yes, I can help you.

I actually have a 24v system in my coach, so, I've been there...

First, I recommend you read the following posts about Installing a system in phases and Solar System Affordability:

Installing-a-Solar-System-in-Phases

Affordable-Solar-How-To-Design-and-Install-an-Affordable-Solar-System

These two threads will give you a good understanding of some of the issues you are facing.

Second; the advice to leave the 12 volt system alone is solid advice. In my system, I connected my 24v to 12v DC to DC Converter to the same cables that my old Converter was connected to and that is the only interaction my 24v system has with the 12v systems in my coach.

By-the-way, buying 200ah batteries will not save you any space, nor will they save you money, so, I would look at the price per 100ah when buying my batteries and make my decision based on that. Additionally, the smaller form factor of the 100ah batteries may give you more placement/layout options.

With a 24v system, you essentially wind up with two power systems, a 12v system and the 24v system. The 12v system powers everything inside the coach (just like it does now) and the 24v system which feeds the 12v system (via the DC to DC Converter) as well as powers the Inverter and gets recharged by the Solar panels. In your coach you have the on-board Generator which adds a bit of complexity, but if looked at as a separate system can be solved easily.

Looking at your diagram I see one very important issue: You need to have a (whole system) fuse coming right off of the 24v batteries. I see that you have a 400 amp fuse protecting the Inverter/Charger, that fuse needs to be placed within 6 inches of the main battery (actually Buss Bar). Additionally, all your fuses are sized as though you have a 12v system, with a 24v system, your fuse sizes (and cabling) can be reduced by 50%. For example: I have a 150 amp fuse at my batteries that protects my whole system, I also used 1/0 cables from my batteries to my Buss Bars and to my Inverter.

Note: using smaller cables are one of the bigger advantages of using a 24v system.

Important note: my Inverter/Charger is capable of charging at a higher rate than my cables are rated for, consequently, I reduced my charging rate to 50 amps which works out fine because if I am plugged in, my batteries don't need to be charged up very fast. Additionally, this has not been an issue when charging my batteries from my generator, because 50 amps at 24v will charge the batteries plenty fast enough (Solar is my primary source of energy), as a matter of fact, I don't think I have ever ran the generator simply to charge the batteries Solar and Shore Power have been all I need.

Anyway, this should be enough to get you started in the right direction.

I will post later about the best way to handle your Generator

PS: In your diagram, you have a transfer switch leading to the Inverter, you don't need it, the Inverter/Charger has a Transfer Switch built-in.

[willystyle]

Thanks for all that info! I'll check out those resources you linked and look forward to more info about the generator set-up.

[SolarPoweredRV]

Yes, I can help you.

I actually have a 24v system in my coach, so, I've been there...

First, I recommend you read the following posts about Installing a system in phases and Solar System Affordability:

Installing-a-Solar-System-in-Phases

Affordable-Solar-How-To-Design-and-Install-an-Affordable-Solar-System

These two threads will give you a good understanding of some of the issues you are facing.

Second; the advice to leave the 12 volt system alone is solid advice. In my system, I connected my 24v to 12v DC to DC Converter to the same cables that my old Converter was connected to and that is the only interaction my 24v system has with the 12v systems in my coach.

By-the-way, buying 200ah batteries will not save you any space, nor will they save you money, so, I would look at the price per 100ah when buying my batteries and make my decision based on that. Additionally, the smaller form factor of the 100ah batteries may give you more placement/layout options.

With a 24v system, you essentially wind up with two power systems, a 12v system and the 24v system. The 12v system powers everything inside the coach (just like it does now) and the 24v system which feeds the 12v system (via the DC to DC Converter) as well as powers the Inverter and gets recharged by the Solar panels. In your coach you have the on-board Generator which adds a bit of complexity, but if looked at as a separate system can be solved easily.

Looking at your diagram I see one very important issue: You need to have a (whole system) fuse coming right off of the 24v batteries. I see that you have a 400 amp fuse protecting the Inverter/Charger, that fuse needs to be placed within 6 inches of the main battery (actually Buss Bar). Additionally, all your fuses are sized as though you have a 12v system, with a 24v system, your fuse sizes (and cabling) can be reduced by 50%. For example: I have a 150 amp fuse at my batteries that protects my whole system, I also used 1/0 cables from my batteries to my Buss Bars and to my Inverter.

Note: using smaller cables are one of the bigger advantages of using a 24v system.

Important note: my Inverter/Charger is capable of charging at a higher rate than my cables are rated for, consequently, I reduced my charging rate to 50 amps which works out fine because if I am plugged in, my batteries don't need to be charged up very fast. Additionally, this has not been an issue when charging my batteries from my generator, because 50 amps at 24v will charge the batteries plenty fast enough (Solar is my primary source of energy), as a matter of fact, I don't think I have ever ran the generator simply to charge the batteries Solar and Shore Power have been all I need.

Anyway, this should be enough to get you started in the right direction.

I will post later about the best way to handle your Generator

PS: In your diagram, you have a transfer switch leading to the Inverter, you don't need it, the Inverter/Charger has a Transfer Switch built-in.

In re-analyzing your diagram, I see that the ATS is feeding your Inverter and the ATS is controlling the output from Shore Power or the Generator. This is the appropriate connection and the ATS inside the Victron Inverter will control the switching of power between that (ATS) input and the batteries.

Now, onto how to best provide power for the starter on your Onan Generator...

I need to first know if the Generator has it's own Starter Battery, or if it relies on the main 12v battery that powers the whole coach. The reason I ask is because your new system is going to need to charge that battery and the way that battery operates will dictate how we approach this problem.

For the sake of this discussion, I am going to presume that your main 12v battery(ies) are providing power for the Generator to start (and there is not a separate 12v starter battery dedicated for starting the Generator) [ I know I am repeating myself, I just want to be very clear].

If you choose to do what I did and remove the OEM Converter and simply attach the DC to DC Converter to the output wires of the old Converter (note: ensure the wires are capable of handling the entire 85 amp output of the DC to DC Converter [your Converter is capable of producing 15 amps of surge power]), you will be supplying charging power to the battery terminals where the original 12v battery was installed.

In order to make charging the Starter battery easier, I suggest you eliminate the Lead Acid battery and replace it with a 12v Lithium battery. You might need two Lithium batteries to actually start the Generator. Some people have reported that one 100ah Lithium battery is enough and others have reported that 2 Lithium batteries make the Generator easier to start, I'd start with one and add a second if you think the generator is struggling.

Here is where we get a little bit technical...

Most Lithium batteries have a 100 amp (not amp hours) discharge rate, this is even true for some of the 200ah batteries. This 100 amp discharge rate refers to the maximum amps the BMS will allow the battery to supply at any given time. Many batteries may be rated at 100 amps, but they have a 150 or 200 amp "burst" discharge rating for a few seconds. The Starter motor on your Onan will use every bit of this 100 amps and more.

So, the trick, is to find a battery that can provide maximum amps of power to start the Generator, while not spending a lot of money. Note: you will have an additional 70 amps of power provided by your DC to DC Converter.

After doing a quick search, it seems like the best solution is to install 2 100ah batteries to start your Generator. The good news is that you can use these two batteries to supplement the power for your coach, all you have to do is install a simple on/off switch on your DC/DC Converter and these batteries will feed power to your coach. You can even automate this switchover by using the capabilities built into your (Victron) battery Monitor.

By-the-way, these two batteries will be charged by the DC to DC Converter, they will not get charged to 100%, they will sit at 13.2 volts (or whatever voltage you set your DC to DC Converter to). This will not hurt the batteries and they will still be able to provide enough power to start the generator. You will want to disconnect the 12v charging function inside your Generator because it will provide the wrong charging voltage back to the Lithium batteries.

When you are installing these two batteries, you will want to connect them to a pair of Buss Bars and then connect the starter cable to the Buss Bars, this way, each battery can provide it's full 100 amps of power to the starter and not get limited by the internal BMs of the battery that the starter cables are attached to (be sure to fuse the starter cables).

If your Generator has a dedicated Starter battery, then we have a whole different discussion.

Of course there is another way to solve the Generator issue...

You could upgrade your starter to 24 volts and simply provide power directly from your 24v battery bank. In your situation, you would not need to upgrade the internal Onan alternator to 24v because you won't need to have the Generator recharge the 24v battery because, the Inverter/Charger will be recharging the battery. This might be cheaper and easier than adding a pair of Lithium batteries just for starting the Generator. By-the-way, 24 volts should start the generator much easier.

Again, I will pause here to let you digest all this...