Coach Electrical Systems

PNWorBUST72 · February 15, 2018, 10:48:05 AM

So I understand this coach I am looking to buy is a 24v system, can I replace the 2 24v batteries with 12v or is the 24v a requirement because of the size of the engine/coach itself?

Or is it simply use 24v for the coach side and then ad 12v for the RV side?

chessie4905 · February 15, 2018, 11:04:02 AM

The batteries are 2- 12 volt, wired in series to produce 24 volts.

PNWorBUST72 · February 15, 2018, 11:24:15 AM

So for the chassis side use 12v with good cca to start and then deep cycle with high amp hours for the RV side.

Gonna have to start to figure out AC and refrigerator requirements here soon...

richard5933 · February 15, 2018, 12:56:00 PM

I'm setting up a house battery bank on a 4108, which is a 24v system. My bus has two 12v start batteries wired in series to make 24v. If your system is the same, then yes, you would use two appropriately sized 12v batteries for your start batteries.

For your house batteries you have choices to make. I'm going with a 12v system and will be using four L16 six volt deep cycle batteries wired in series/parallel to provide 12v output. The same four batteries can be wired to provide 24v. The choice really depends on how you intend to use the power downstream. Your choice of 12v or 24v for your house system will also determine how you charge the house batteries and whether you can (easily) charge them from the bus alternator.

bobofthenorth · February 15, 2018, 01:42:18 PM

This has been discussed .... often. So start out by using the search function. There's reasons to stay with a 24 volt house bank and there's reasons not to. Only you can decide which side of that divide you will land on. After you have used the search function for a while you may wish to come back and ask more questions but for now you'll learn more quicker with some searches.

gumpy · February 15, 2018, 02:52:06 PM

I suppose it might help us to know what the bus is you are looking at.

In general, if it's a 24v system, it was designed that way for a reason, and would be difficult and expensive to change it to a 12v system.

As for the house system, you will have to decide which way you want to go. As already said, there are pros and cons for each voltage on the house system.

PNWorBUST72 · February 15, 2018, 04:16:52 PM

Ok first, thanks search was helpful but I think I have more questions than before.

So I am looking at a 1978 MCI8, it appears to be full 24v lights etc.

I had assumed that if the bus we built with 24v that changing ould be difficult but in some of the posts I noticed people saying 24v bulbs and accessories were hard to come by too.

I dont THINK changing the entire chassis side bus/wiring to accommodate a 12v system is in my future but is it hard to find 24v LED lights or appliances, etc or do people just create another "leg" in their electrical system just for 12v? There is hardware needed for that conversion yes?

eagle19952 · February 15, 2018, 04:33:36 PM

Quote from: PNWorBUST72 on February 15, 2018, 04:16:52 PM
Ok first, thanks search was helpful but I think I have more questions than before.

So I am looking at a 1978 MCI8, it appears to be full 24v lights etc.

I had assumed that if the bus we built with 24v that changing ould be difficult but in some of the posts I noticed people saying 24v bulbs and accessories were hard to come by too.

I dont THINK changing the entire chassis side bus/wiring to accommodate a 12v system is in my future but is it hard to find 24v LED lights or appliances, etc or do people just create another "leg" in their electrical system just for 12v? There is hardware needed for that conversion yes?

simply put, the 24v system, as it is for the existing systems, as designed when new...cannot/should not be changed to 12v....(it could be but would cost a small fortune)

the house system, IF an inverter is in your future, can be either 24v or 12v. your choice, BUT, again, more cost effective to "keep it 24v" if that is what is the current chassis system is..

gumpy · February 15, 2018, 04:40:04 PM

First, yes, a 78 MC8 is 24v bus system and the headlights were 24v. They are hard to find, and expensive. It is possible to change the headlights to 12v bulbs, running in series on the 24v system. MCI came out with a modification sheet explaining how to do it. All other lights (clearance, turn signals, tail, brake) can also be converted to 12v, and LEDs are readily available. You just have to know how to get your 12v without endangering the 24v battery. An equalizer would be the first thing to look at.

richard5933 · February 15, 2018, 05:08:26 PM

Keep in mind that a 10w bulb on a 12v system will draw twice the amps as a 10w bulb will on a 24v system. Wiring gauge is sized according to the amps being drawn through it, so it's important to keep in mind the size of wiring for any circuits you plan to convert from 24v to 12v. If you go from incandescent 24v to LED 12v I imagine that the current draw would be reduced, but it's something to pay attention to.

There are a few great threads on how to get 12v from a 24v system. It needs to be done correctly to keep the draw & charge on the batteries even, hence the reason many people use an equalizer to accomplish things. I decided to go with a 24v to 12v battery-to-battery charger, something which seems controversial to some but will work for us.

What I'm trying to say is that there are many ways to do this which will work well. Explore some of the marine suppliers as well as the RV suppliers to see more 24v appliances.

PNWorBUST72 · February 15, 2018, 05:44:46 PM

Well my thought here was to keep anything 24v on the bus as OEM, 24v.

But to add a 12v system for the interior lights/switches/appliances.

It seems that the issue is how to keep the 24v chassis batteries and the 12v coach batteries charged correctly?

buswarrior · February 15, 2018, 06:58:04 PM

Before you choose a voltage for the house...

What do you want to accomplish?

Your order of decision is wrong.

What is this "interior lights/switches/appliances" stuff you speak of?

That's far far from enough information to ignore the 6000+ watt alternator on the coach...

We try NOT to blindly duplicate the foolishness in stick and staple RV's in our bus conversions...

Happy coaching!
Buswarrior

csrddcd · February 15, 2018, 08:24:45 PM

If you do decide to tap 12V off the 24v chassis batteries to run something, be careful how you do it. The po of our rig had tapped one of the two batteries to supply 12V to several things and the brand new 8D batteries that he included the day we bought the rig were giving us grief only 8 months later. I did verify proper alternator output and good connections, ground and water levels. It turns out that the batteries he replaced were hardly more than a year old as well.

Without a equalizer, the alternator supplies equal juice to both batteries, continually creating a uneven charge between the two batteries, thus apparently leading to their early death.

We replaced the batteries and installed one of these https://www.amazon.com/gp/product/B01LYK6G2Y/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1 to obtain 12V from across both batteries, thus solving the problem.

You may not need a 40 amp unit (other sizes are available at less cost), we were using this to run a military grade electric heater for windshield defrosting and needed the extra juice.

csrddcd · February 15, 2018, 08:28:18 PM

Forgot to add that the unit in the link was way, way, way, cheaper than the equalizer, which also would have been another way to address the problem.

PNWorBUST72 · February 15, 2018, 08:58:14 PM

I was planning, before the 24v detail I missed took us South, to add a bank of 12v batteries on the Coach side to run but not sure thats viable anymore.

My goal here was to run 12v all through the coach for lights, charging ports, 12v RV appliances, leaving the Chassis side as is at 24v. But other then the obvious 12 vs 24 I dont understand the differences that would impact that system.

I am looking at this and it seem 24v on BOTH sides is the best option:
http://jdfinley.com/electrical-system-design/