New ambulance wiring question - Do I need to separate the batteries to have a 'house bank'

[rewired]

We recently purchased a 2007 Horton Type 3 ambulance based on the Ford E450 Super Duty 6.0 TD. We've had starting issues when not on shore power, so I pulled the 3 Motorcraft BXT65-850 batteries and took them to be tested at Oreilly's Auto Parts. All 3 are within the 3 year replacement warranty period, but they will not cover under warranty because I didn't buy them (even though the manufacture dates are 1/18 and 2/16). I have 3 new NorthStart built X2Power Premium AGM Batteries (930 CCA with 4 year free replacement) on order at Batteries Plus to replace them.

The ambulance has a manual battery disconnect switch on the side of the driver's seat, and all wiring appears to be led to the electrical box behind the driver's seat. There is oe very large cable running from there to the battery tray on the passenger side where the 3 batteries are wired in parallel.


I've confirmed that there is no other starting battery by disconnecting the main lines to the battery tray and cannot find a battery isolator anywhere.

Do I need to separate the batteries (1 for starting and 2 for house?) by installing a battery combiner (possibly the Victron Intelligent Battery Combiner) or do I need to an Automated Charging Relay (ACR)?

I'm assuming that I would have to disconnect the module in the wiring box behind the seat and install a second set of battery cables between the box behind the seat and the house battery bank, then use a battery combiner or ACR to charge both when plugged in to shore power or the vehicle is running.

Has anyone done this?

Any guidance on the wiring changes needed would be sincerely appreciated!

Tony

 

[Len.Barron]

Depends on how elaborate/convenient a system you want. First you need to determine if you need more than one starting/chassis battery, looking at the specs of the new batteries you are buying I'd say just one is plenty for that 98% of the time. If so you could just install a high capacity manual cut out switch (blue sea 9003e is what I use) on the positive leg in between the single starting/chassis battery and the two remaining house batteries.
You can then install a simple battery isolator(any rv parts supplier will have many to choose from) that will allow you single alternator to charge these banks independent of each other. If you get in a jam and have killed one or the other bank you can close the cut out switch and use it as a built in "jumper/combiner" function.
Obviously you'd have to run another positive lead and split any connection between starting/chassis and house loads.
I went a step further on my build, with the duramax there is a factory option for dual alternators so I sourced those parts and have two completely independent systems, I do have the cut out/jumper/combiner switch I mention above in case I have a problem with one system the other is sized to completely cover it.

 

[rewired]

Thanks, Len!
Mine has the dual alternator option installed (95/140 amp upper and 75/120 amp lower).
Thankfully, I was also able to pick up set of all 3 FSMs on ebay for less than $100 that should make tracing the factory wiring easier.

I like your separate systems approach... I guess my biggest challenge will be tracing the ambulance wiring to determine what needs to be left in place and what needs to be rewired to properly separate the systems.

My battery order got delayed, so I may have to go with a single bank of 3 for our upcoming trip to the Smokies, but I'll start tracing and diagramming to map out the split system design.

Tony

 

[cjken]

I’ve got two starting batteries under the hood that are always connected to the chassis then two “house” batteries that can be isolated from the system with the disconnect switch to just power the box.
I usually flip the disconnect switch if I’m camping or parked for extended periods so that I always have starting batteries available.

 

[yager]

For me I have a separate batteries for the truck AND the house.
I have friends that stop over and the do not understand solar / nor the how the batteries work.
They throw a switch and light coming, or the plug in and do something.
All of which, i don't care BUT regardless i can start the truck up.
I have a cross connect to where i can 'trickle' charge the truck, when i want and i unplug it on trips.
YMMV [Your Mileage May Vary]

 

[rewired]

Thanks, everyone!
My batteries surprised me by getting to the store today so I spent part of the afternoon charging (they all went to Float within 15 minutes), cleaning cable ends, installing new terminal connectors and getting them in the battery box.

The new batteries are Northstar built AGMs and weigh in at 60 lbs each instead of ~47, so I'm hoping the extra lead will help in the short term...

Unfortunately, it appears that Ford went to dual chassis batteries with the introduction of the 6.0, which were replaced by the 3 battery box on my Horton. The FSM for the 2007 doesn't even indicate that an under hood battery was available with the 6.0. (Starting to wish I'd looked longer for a 7.3 PSD).

Since all of the major wiring comes together (in mine) behind the driver's seat, I'm thinking that as I map out the wiring and plan for house batteries, I may look at leaving the tray batteries alone (except at the interconnect) and look at installing one 4D/8D 200-250 AH battery in the driver's side compartment with the other electronics. This would allow me to keep the cable runs shorter (interconnecting behind the driver's seat) and give me easier access to the shore power/charger/inverter/interconnect wiring. It looks like the 4D/8Ds would fit there, and my battery tray is 3/4" too short to replace one with a 4D/8D.

My wife wants running water (not poured out of a can) pretty quickly, so I may have to plan and save up for the house batteries as the next project after that.

Tony

 

[rewired]

Thanks for the tip on the negative cable!
I'll relocate it tomorrow morning.

Tony

 

[Ozrockrat]

I am on my 5th ambulance and have never split the house an vehicle batteries. Having them all together gives you a much better discharge surface. You are better off spending your money on solar and getting in the habit of turning off the isolator. (Very important)

Don’t worry there are plenty of other projects to burn up your time and money without fixing things that are not broken.

Also an essential tool for chasing parasitic loads on these rigs is a DC clamp meter. I use this one but I am sure there are cheaper versions around.

https://www.amazon.com/Auto-Rangin...SY340_QL65&dpPl=1&dpID=41Q4lodtN1L&ref=plSrch

 

[rewired]

Thanks, Ozrockrat!

I have this one
https://www.amazon.com/gp/product/B01IB4N3YG/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

but my batteries were too shot to even get consistent readings. I'm hoping the new batteries will resolve that issue so I can look for power leaks this weekend.

We have a 2k generator I can take (along with a DeWalt charger that will handle AGM batteries) for any over-discharges I have in the short term. I have ordered LEDs for all of the interior lights, so my draw from them won't be too bad soon. My main concern is how much drain our chest refrigerator will cause (it's 55 watts with compressor at max). I also have a 'KillaWatt' meter to monitor the overnight draw from the refrigerator.

This is the one I have on the way
https://smile.amazon.com/gp/product/B07FMC4LFW/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

The reason I risked it on this one (along with the Amazon warranty) over the Dometic and ARB are:
1. almost $500 cheaper (I hope don't find out why the hard way)
2. it's almost 6" shorter lengthwise, so it fits between my shelf racks in the rear driver's compartment (we can reach it from inside while moving)
3. the controls are on the top, so we can adjust it without removing it (like the Dometic)

Once it gets here, I'll be happy to do a separate thread on how it performs.

Tony

 

[Len.Barron]

I'm just keeping mine as simple as possible. An isolation/shutoff switch for each bank and a jumper/combiner switch. With dual alternators they will run completely separate unless I want/need to tie them together.

 

[luthj]

I suggesting those with multiple parallel batteries in the same bank read this link, and apply the techniques to balance the wiring in the bank.
http://www.smartgauge.co.uk/batt_con.html

There is a significant reduction in battery life when the bank is not balanced.

 

[Bikersmurf]

To be the devil’s advocate... By disconnecting the battery under the hood, all you really proved is that isn’t another functioning battery. On many rigs the second battery is forgotten, dies, and then it drags the second one down. So search high and low and follow all the heavy lines.

I don’t know about a 6.0, but with a 7.3, I’d not go down to one starting battery. I’d keep your 3 house batteries and mount a second starting battery in a OEM battery box along the frame rail. Yeah you’d end up with 5... but more is bedda. I’d then pick up a Blue Seas ACR which will combine the batteries for charging but never be left combined. The 120 I’ve got works well, but to do it over I’d get the bigger one.

 

[rewired]

Luthj,

Thanks for the link!
I've moved the negative cable as Verkstad suggested. I'll see if I can figure out a way to balance the middle battery.

Bikersmurf,

I don't have an under hood battery that I can find, just the 3 in the tray. According t the FSM, they didn't offer an under hood battery in the 6.0 PSD...
I'll be out again in the morning (working on replacing fluorescent bulbs with LED and installing fridge). I'll see if I can crawl under and follow cables to see if I can locate one that's somewhere I haven't seen yet.
I'll also measure to see if there's room to install one of the factory boxes on the frame.

Len.Barron,

It looks like you've got a great setup!

Tony

 

[luthj]

If you moved the negative, then all is well. The three batteries all have the same resistance/length of cable, and will share loads and sources equally.