E350 Ambulance Wiring... Batteries and Alternator

[Bikersmurf]

Anyone know how the wiring in a 1997 E350 ambulance is supposed to be connected?

I've found that my starting batteries drain along with the house batteries... & that the (+) of the starting battery under the hood is connected to the center conector of the battery Isolator. Furthermore, when I disconnect the two house batteries, all the house systems still have 12.3 v.

I need to dig deeper, but in a nutshell, I'm trying to sort out how the 215amp alternator is supposed to be connected and to which terminals so that all the electronics work right.


1) All the batteries are new.
2) Alternator is new and puts out 14.1-14.2 volts.
3) The Diaode isolator is not ideal, but that's what I've got to start with, and I'd like to have it wired right before I try to get rid of it.
4) 7.3 PSD, Mitsubishi 215 amp, 1997 E350, Crestline 'New Era' ambulance, 2 starting & 2 Marine batteries.

 

[Bikersmurf]

Looked at it some more. It looks like a PO ran the original wire from the alternator directly to the starting battery because they weren't using house batteries. And then, the next PO ran a new 4 guage wire from the battery to the junction point on the fire wall where the original alternator wire connected. Which explains why there are 5 (4 guage or larger) wires connected to the main starting battery. Once I confirm all the wires are going where I think do, I'll rewire and test to make sure all the batteries will get charged... And that the Guages will work.

 

[flightcancled]

If you look in my build I had to do a rebuild and conversation to a ACR. In a nutshell the batteries in a bank should be connected together and then have a positive wire going to one of the outside terminals on the isolator. The center pin goes to the van circuits.


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[Bikersmurf]

"Van circuits"? Most seem to indicate alternator.
Currently mine has starting battery connected to center pin and the starting battery drains along with house battery.

I'll check out your build thread.

In the future, I may convert to ACR, but I tend to prefer manual control... And finding an ACR unit that can handle the Alternators output may be a challenge.

Edit: looks like Blue Seas is rated for 350 continuous... Should be enough to handle the 215 amp Alternator... And 1000 amps should be enough to crank the 7.3 diesel.

 

[flightcancled]

What I mean is that the center pin is your output, so anything that needs power should be downstream from that center pin unless you want a separate control panel on your house battery bank or something.

So far so good with my Blue Sea ACR despite my reluctance to make the switch. I also was worried whether it would be able to handle the loads, but really a boat is set up just like an ambo and has similar power needs.

The ACR frees up some space which I like too. Also definitely getting a much smoother start and a lot more power from my deep cycle house batteries.


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[Bikersmurf]

Isn't the Center the input from the alternator?

 

[dwh]

If you have a diode-type isolator - the one with the heatsink that you find on the shelf at any auto parts store - then usually the output from the alternator goes to the center and then the isolator splits it out to both chassis and house batteries.

If you have a solenoid-type isolator, that's a completely different beast. With a solenoid type, the alternator output goes to the chassis battery as normal, and then a line from the chassis battery + goes to one of the big terminals on the solenoid, and a line from the other big terminal goes to the house battery +. An ignition circuit goes to one of the small terminals on the solenoid. When the key is on, the solenoid is engaged and it ties the large terminals together - thereby tying your batteries into a single "bank" and both get charged from the alternator.

In other words, the solenoid is just a big switch with a small electromagnet to activate the switch. When the electromagnet is energized by power being applied to the small terminal, the switch connects the big terminals together. When the key is off, the electromagnet is deactivated, the switch is open and the batteries are "isolated".

Some solenoids have only one small terminal, that's for + to energize the electromagnet when the key is on, and the electromagnet grounds through the mounting strap. If it has two small terminals, you use one for + (key activated ignition circuit) and one for - (to ground the electromagnet) Doesn't matter which you use for hot and which for ground.

 

[dwh]

If you have a solenoid rigged so that power is constantly applied to the small terminal, two things happen - A) the batteries are always tied into a single bank, and B) the solenoid electromagnet is constantly sucking about an amp per hour out of the batteries.

 

[Bikersmurf]

I've got a Diode type isolator with a Massive heat sink... About a foot long

I know it limits voltage to the batteries, but charging is supplemented by a 60 amp 3 bank charger.

 

[Bikersmurf]

Hooked the Alternator to the center pin of the isolator. The voltage loss doesn't seem so bad... 14.6-14.7 v@ Alternator, 14.07 v at each battery bank.

 

[DiploStrat]

Typical diode voltage drop. Bad news is that you will have to drive all day to get much charge. You REALLY need to lose the diode isolator.

 

[Bikersmurf]

The drop isn't as bad as I thought... Being 14.07 at the battery, I know it's not ideal, but eliminating it isn't at the top of my list.

 

[DiploStrat]

It should be high. You may wish to consider this: http://www.sterling-power.com/images/downloads/advancedcharging.pdf

All your diode is doing is producing more heat under the hood. With 14.6v (depending on the temperature at which you measured) you really should be using a relay based system. Cruise over to the 12v forum for lots of blood on the carpet and useful info on this subject. (Over which, some of us obsess way too much!)

 

[Bikersmurf]

An interesting read... Perhaps even enough to bring it up the list somewhat, however, since the alternator continues to deliver over 14 volts to the batteries even when it's hot... It worked that way as an Ambulance for 10 years, so it can wait a bit.

Still these come first since I don't use it as a camper much:
1) Horn... Mysteriously started working a week after I bought the truck... Stopped mid honk after I'd had the doghouse off to fix the alternator wiring.
2) No crank issue that shows up at random, and so far has been resolved by a thump on the dash.
3) Interior... Minimally functional.

 

[flightcancled]

It didn't matter for the EMTs because they don't really use any power with the engine off during their shift, then plug it into the wall after. I justified it to myself by looking at how much longer my batteries will last by upgrading to an ACR which will outlast the vehicle.

Someone else was experiencing the same problem. Can't remember what thread it was though.


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