New member, new bus. Couple electrical questions

scooter01922 · May 06, 2020, 09:27:03 AM

Hello all, i recently picked up a mostly converted 1989 MCI 96A3. Shes a pretty cool bus and is going to be just the thing for me and the wife to make some excursions to see more of this great country, after this whole coronavirus thing blows over of course. The previous owner didn't own it for long and he didn't get any info from the guy that actually did most of the conversion so theres a bit of detective work to do. Most of it i'll just have to muddle through myself. I was however wondering if anyone can help me make heads or tails of this batter box. I have a couple wires, one descent size that don't appear to actually do anything but clearly they are there for a reason. For some reason the clearance lights don't come on with the dash switch but they did come on when you connected the house battery. Or at least they used to, i put a fresh battery in there when i got it home and now no clearance lights and the generators won't start. They crank, but no spark. I wish whomever started this project left some notes

I highlighted the wires in question on the last pic. 2 are barely connected and one has a 3 position switch inline that appears to change absolutely nothing.

richard5933 · May 06, 2020, 10:00:29 AM

I'm assuming that those two 8D batteries are BOTH part of the chassis battery system being run in a series format to provide 24v.

Also looks like some of the smaller wires might be tapping into the center of the two batteries to provide a 12v feed to something(s).

Do you have another set of house batteries somewhere?

Have you confirmed if your clearance lights are 24v or 12v? You can probably pull a bulb to check what's in there right now if you don't already know. What about your headlights? 12v or 24v?

Lots of people have done lots of bad things to wiring systems since these buses left the factory. Hard to know exactly what goes where without lots of sleuthing.

A good multimeter and a wiring diagram help greatly.

luvrbus · May 06, 2020, 10:11:40 AM

The Vanner blew a fuse, some have a reset button or the Vanner could be bad

scooter01922 · May 06, 2020, 10:28:19 AM

You are correct, those are the start batteries 24V. Yes, someone did tap into them several places. As it sits is how i found it, figure i would start there and try to figure out what may have been done wrong at some point. I would have to guess all the clearance lights are 12v as they only came on when you connected the separate house battery, only one at 12v. Odd for sure, but who knows what they were thinking. Where the heck is the vanner?? I have seen plenty of pics with them right there above the battery but not on this bus. All i have is that 10 amp breaker to who knows where.

buswarrior · May 06, 2020, 10:29:37 AM

Welcome to the party!

You want to get one of those wire tracers that puts a signal thru the wire, so you can find the other end. Harbour freight has cheap ones in US.

That red wire that connects the two batteries together is too small. Typically, the main cables should be 0000 size cable.

Be aware that there is more than sufficient energy to burn the bus down, if you don't get these wires traced and identified as to their purpose.

Be safe, and leave the cables off the batteries when you aren't working on figuring it all out.

Working backwards from the coach electrical schematics, identify what is correct, and reduce the uncertainty.

Happy coaching!
Buswarrior

buswarrior · May 06, 2020, 10:37:32 AM

That wire with the fuse mounted above... has that been connected to the negative/ground post?

Where are these "house" batteries you mention? Those two batteries in the pictures are the coach chassis 24 volt set, not a house and chassis battery side by side.

When wires are not labelled, they end up attached to the wrong places very easily.

I am a big fan of these being collected on a bar, with the battery connections being simplified to as few as possible, because even smart guys screw this stuff up, when swapping batteries.

What is the voltage of each battery? Both should be higher than 12.6 volts with a multi-meter.

Happy coaching!
Buswarrior

scooter01922 · May 06, 2020, 10:48:22 AM

Theres a house battery in the rearmost compartment along with the water system. Both of those are chassis batteries, the PO replaced them not long ago, recent date codes. That jumper wire bugs me, already ordered up a heavy duty replacement. Positive and negative terminals look like crap too so those will be getting changed before she really goes anywhere too. Good suggestion on the wire tracer, should have thought of that. That one connected to the ground is what had me start looking closer, and then all these other things that didn't look right started becoming evident. I'm a big fan of simplicity with batteries. I have far too many projects to remember what hooks up where when it comes to some things that don't really need a battery in them all the time. I'll simplify when i figure out what goes where LOL

freds · May 06, 2020, 11:14:03 AM

Also never a good idea to tap 12V out of 24V series battery bank; as it can get the two batteries out of balance, depending on the draw.

Also if it is used for house systems, you can draw down the one battery down to the point where you would not be able to start your bus.

Your start batteries should only be used for one purpose, starting the bus!!!

Some conversions have both 12V and 24V alternators; with house RV systems off of the 12V system.

If the bus only has a 24V alternator then the ideal power flow would be:

1. Alternator output
2. Battery isolator with for dual battery banks to split the power to:
A. Start batteries and bus 24V system
B. 24V to 12V DC to DC converter
3. The output of the DC to DC converter would then be hooked to the 12V house battery bank.
4. 12V house battery bank would be protected from over discharge by a battery protect module.

You need to size the battery isolator according to the alternator output. Here are some example parts:

https://www.amazon.com/Victron-Energy-Battery-Isolator-Batt/dp/B00NT9MTMQ/ref=sr_1_5?dchild=1&keywords=200%2Bamp%2Bbattery%2Bisolator&qid=1588787621&s=automotive&sr=1-5&th=1

https://www.amazon.com/Renogy-Isolator-Compatible-Lead-acid-Batteries/dp/B07JQ98RQJ/ref=sr_1_6?dchild=1&keywords=200+amp+battery+isolator&qid=1588787621&s=automotive&sr=1-6

Here's what I use for my DC to DC converter (not exactly in this scenario).

https://www.amazon.com/gp/product/B01BF5BQLA/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

In my application I then protect the 12V house battery with:

https://www.amazon.com/gp/product/B07LGCY3RR/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Also note that the battery isolator depending on manufacture can have a 0.5 voltage drop; so, you may need to adjust the voltage regulator with it in the circuit.

richard5933 · May 06, 2020, 11:23:19 AM

Might be a good idea to invest in a hydraulic cable crimper and a few sizes of copper lugs - then you can start making your own cables as needed. I found quickly that having to order cables every time I wanted to move something around got old (and expensive) quickly.

scooter01922 · May 06, 2020, 12:21:54 PM

Quote from: freds on May 06, 2020, 11:14:03 AM
Also never a good idea to tap 12V out of 24V series battery bank; as it can get the two batteries out of balance, depending on the draw.

Also if it is used for house systems, you can draw down the one battery down to the point where you would not be able to start your bus.

Your start batteries should only be used for one purpose, starting the bus!!!

Some conversions have both 12V and 24V alternators; with house RV systems off of the 12V system.

If the bus only has a 24V alternator then the ideal power flow would be:

1. Alternator output
2. Battery isolator with for dual battery banks to split the power to:
A. Start batteries and bus 24V system
B. 24V to 12V DC to DC converter
3. The output of the DC to DC converter would then be hooked to the 12V house battery bank.
4. 12V house battery bank would be protected from over discharge by a battery protect module.

You need to size the battery isolator according to the alternator output. Here are some example parts:

https://www.amazon.com/Victron-Energy-Battery-Isolator-Batt/dp/B00NT9MTMQ/ref=sr_1_5?dchild=1&keywords=200%2Bamp%2Bbattery%2Bisolator&qid=1588787621&s=automotive&sr=1-5&th=1

https://www.amazon.com/Renogy-Isolator-Compatible-Lead-acid-Batteries/dp/B07JQ98RQJ/ref=sr_1_6?dchild=1&keywords=200+amp+battery+isolator&qid=1588787621&s=automotive&sr=1-6

Here's what I use for my DC to DC converter (not exactly in this scenario).

https://www.amazon.com/gp/product/B01BF5BQLA/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

In my application I then protect the 12V house battery with:

https://www.amazon.com/gp/product/B07LGCY3RR/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Also note that the battery isolator depending on manufacture can have a 0.5 voltage drop; so, you may need to adjust the voltage regulator with it in the circuit.

WOW, thats a lot of info for one post. THANKS
I have a friend that buys a lot of govt surplus stuff and he has a rather large 24 to 120 converter that came from i think an ex police boat. He really has no use for it so offered it to me, might have to see about having a 24volt house battery bank. So i'll have some juice to keep the fridge cold running down the road. Then dropping some down to 12v for the few things that are 12volt. As far as i have ascertained the only 12v i need is for the lighting via LED, the water pump and to start the generators. I only have the bus alternator at 24V for charging at the moment.
Whoever did most of the work did a descent enough job for the most part. There are just some things that leave you wondering though. I was just out poking around on it. The one wire on the negative with the switch runs the length of the bus only to be capped off in the rearmost bay. Thats one figured out...no idea what the deal was with that but whatever. Generators started, seems that the pesky automatic choke mechanisms are not so great. Little shot of ether and they both fired right off. It has a pair of 5500w gas rv gen sets in half of the front storage bay. Why 2?? You got me, not a clue. My guess is that it was a LOT cheaper than one larger diesel generator.

scooter01922 · May 06, 2020, 12:23:48 PM

Quote from: richard5933 on May 06, 2020, 11:23:19 AM
Might be a good idea to invest in a hydraulic cable crimper and a few sizes of copper lugs - then you can start making your own cables as needed. I found quickly that having to order cables every time I wanted to move something around got old (and expensive) quickly.

Yeah, you aren't kidding. For what they cost large battery cables ought be gold plated !!
Fortunately the 8 inch jumper i needed was cheap enough at the place i order my dump truck parts.

luvrbus · May 06, 2020, 12:32:20 PM

A Vanner is battery equalizer and will keep the batteries equal that bus should have one some place for the head lamps unless the PO design his own system People leave the system 24v and will draw 12v from the Vanner which is not a good idea even though it has a 12v terminal.you have work ahead of you trying to figure that one out for sure

scooter01922 · May 06, 2020, 12:41:53 PM

What kind of juice is the vanner drawing?? Any chance that wire running up the the 10 amp circuit breaker runs to it or are we talking a lot more capacity?? Just looked all over the place and see no vanner, but also don't see much monkeying with the stock wiring, which is good.

windtrader · May 06, 2020, 09:55:04 PM

Welcome to the world of owing a bus. This is one of a small handful of site with lots of real world expertise so make sure to bookmark and visit often.

Quote from: luvrbus on May 06, 2020, 12:32:20 PM
A Vanner is battery equalizer and will keep the batteries equal that bus should have one some place for the head lamps unless the PO design his own system People leave the system 24v and will draw 12v from the Vanner which is not a good idea even though it has a 12v terminal.you have work ahead of you trying to figure that one out for sure

BW, I probably misread your comment about how to connect and use a battery equalizer like a Vanner 24v to 12v unit. Isn't the purpose to step down the voltage in a way that keeps the 24v source in balance, use the 12v output terminal to feed 12v devices in the bus?

buswarrior · May 07, 2020, 06:37:23 AM

It is probably better to think of a battery equalizer as a device that keeps the batteries equal, not so much as supplying power for other things.

You take the power from one of the 2 batteries in a 24 volt set, a centre tap.

The equalizer works at correcting that imbalanced theivery, with it being connected to both sides of both batteries, by working the stronger battery to bring the weaker one up to match it.

A 24 to 12 volt converter is going to work both batteries at the same time to provide a separate 12 volt power source. It isn't connected to the centre of the 24 volt battery set, and cares not the health or balance of the batteries. It just consumes 24 volts from the whole set.

If a converter dies, no more 12 volts

If an equalizer dies, you still have power, but will eventually have battery life problems, because of imbalanced charging and discharge. IF you don't do any periodic inspection of your electrical, which is always a busnut problem...

The multimeter will quickly show you your batteries aren't equal, if you bother to check once in a while. Equalizer operation is pretty simple, the 12 v connection should be exactly half of the 24 v connection.

With led lighting now, most conversions are using a fraction of the power we did a few short years ago, with incandescent bulbs burning everywhere, so the 12 volt loads are historically much smaller than they used to be. I don't think most users need a dedicated 12 volt power supply, an equalizer and centre tap takes care of business?

Happy coaching!
Buswarrior