2013 E-350 5.4L Ambulance battery draw?

Matt Saunoras · April 3, 2015

This is the first ambulance I've ever checked for battery draw and I'm not sure what I should expect to see. I don't really have a like unit to compare it to either. I verified it though and it will drain the batteries if it sits for a few days.

After everything powers down it will continuously draw 560 mA. Seems excessive to me but I'm not sure. As far as I can tell its not anything factory either. Removed every fuse one at a time with no significant change.

Bruce Amacker · April 3, 2015

That's 10-20 times what the parasitic draw should be, use an amp clamp on wiring to find what's drawing, don't forget possibilities of a shorted alt and other items that can cause draw. Checking voltage drop across fuses is better than pulling them out, you'll get a small vdrop on the fuse terminals if the circuit is pulling any current.

Call the cust and ask them if they keep it plugged into shore power while parked, many times there's a refrigerator (for meds) and other things that are alive 24/7 and they plug them in to 110v while parked to keep the bats up.

Good Luck!

Keith Browning · April 3, 2015

Normally ambulances have a main power switch / module disconnect that turns off all power to the body and all equipment. All of the new models are electronic now. As Bruce said though, there may be some vehicles with equipment that requires constant power. You need to determine this first. Then approach parasitic drains as you would any other Ford vehicle; <50 milliamps after 40 minute shutdown time.

Good luck.

Matt Saunoras · April 3, 2015

I did not disconnect either alternator but it had crossed my mind. I will dig into this thing further when I get a chance. Something isn't powering down like it should I just haven't found it yet.

I hadn't thought of the amp clamp idea, I'm not sure we have one that will pick up such a small draw but I will find out. I will try voltage drop testing the fuses too. I haven't located the add on fuse panel yet but they sent up the wheeled coach owners manual with it too. I'll look around some more.

Bruce Amacker · April 3, 2015

Sears has a DC clamp on ammeter that's accurate down to 100ma or so for $60 list, that resolution is fine for your needs. When clamping the leads of a draw it's important to only have one of the leads in the jaw of the meter- if you have both power and ground leads your reading will cancel out and show zero.

Good Luck!

Matt Saunoras · April 13, 2015

Found an amp clamp that works off my voltmeter leads. Also located the ambulance wiring behind a panel in the back, what a rats nest. Several things are still powered all the time but nothing was drawing any measurable amperage. Rather than a kill switch there are 2 large automatic shutoff solenoids. Both of those are working fine.

So I went back to where I should have went in the very beginning. Took the air cleaner off, reached my hand down to unplug the primary alt and my arm rubbed the secondary alt. Holy shit it's warm.

Unbolted the positive from it and my draw dropped right down to .042 amps. Put a new secondary alt in it and it's fine. Unfortunately because this is an ambulance I let it cloud my normal thought process. Thanks for all your input guys, I really appreciate it.