Espar coolant heater run time

[EDKtrans]

I have a Espar D4 in my 08 3500 which I use quite a bit. When working I basically live in my truck including most of my sleep time over the course of a few days at a time that I'll be out. I've often wondered just how long I can leave the Espar running and still start the truck again so today I've been running a test.



My normal pattern of use is to be shutting down a warmed up truck and immediately starting the Espar for the night. I then leave it on whatever I'm doing, whether I'm in the truck or eating in a restaurant or whatever. This morning I took the truck out and got it warmed up then once back home I fired up the heater and went about my day working on a motorcycle in my garage. I left the cab heater on as I usually do, set at a comfortable temp with the blower on its lowest setting. This is usually enough to keep me comfortable.



I've been watching the voltage drop... what little there is.



After seven hours I've seen a drop of just 1. 1V, taking the voltage from a starting point of 12. 6V (twin, brand new yellow tops) to 11. 5V. Espar claims the heater will shut off at 10. 5V which means this thing should run for a bit over 13 hours before it shuts down. I don't know if these batteries will have a linear drop and now that its getting dark out, and colder, I'd expect the heater to run a bit more but it stayed pretty cold all day here (high of around 38) and the heater has been running pretty strong all day. Even with these unknowns though I can probably stop worrying about being able to restart the truck after sleeping and being parked for 7 or 8 hours.



My one remaining question is if the truck will start on 10. 5 volts. Anyone know if a warmed up 6. 7L should crank and start on 10. 5V?



Going with my estimate the heater will run till sometime just before midnight. I'll monitor the voltages for a while but will probably give up before that.

 

[Allnew2Me]

A lead-acid battery at 12. 0 volts is about 50% discharged, the most that such a battery should be drawn down to. At 11. 5 you are roughly 80% discharged. Doing this on a regular basis will severly shorten the life of your batteries, especially since our charging systems take a really long time to reach anything close to 100%. You risk sulfation on the plates.

With that said, the truck will start, I think the electronics need at lease 10. 5 volts to work, but if you do this often I would consider adding at least one and probably two additional batteries to your system.

 

[EDKtrans]

Those percentages help make some sense of what I just found. I just went out to check the truck and found the heater had shut off and the voltage was at 10. 5. The truck wont start either, it just clicks and doesn't even try to turn over. I'm about 9. 3 hours into the test but don't know when the heater shut off. Considering its in the mid 30s out now though, and the cabin is still warm inside I'd guess the heater shut off within the last 15 minutes max. Looks like no more than 8 hours without some idling will be my limit.
I've been thinking of installing a couple more batteries in one of the side boxes of my CM flatbed. I was thinking of setting these up on an isolator wired to be in reserve just for starting the truck. Considering the times I've experienced today though maybe they could just be wired in, in addition to the existing two. Doubling the capacity would double my heater run time which would put it out far enough to be a non issue.

Time to fire up the battery charger... .

 

[Shadrach]

Add a separate battery for the Espar and get a deep cycle one, like what is used for RV's. My buddy has a big Wabasto ( 35000 btu ) on his service truck to keep his tools dry and he has 3 extra batteries on the back for it. My Espar D5 is set to max run time of 2 hours from the factory, so no fear of killing my batteries. One of my co workers had his Espar programmed to come one before he left work but he forgot to turn down his heater controls and the truck wouldn't start. Shad

 

[Alaskaskiff]

I ran my espar one tine until the battery low voltage shut it down. The truck would not start and it was a quicker-starting old 12v. Took 4 2 hour cycles on red-top optima's to run down this low. The outside temp was 10 deg F.

 

[Allnew2Me]

The easy way to figure out the proper size battery bank is to check the running amp draw of the Espar heater and the cab blower, then figure out how long it will be running at that draw. That value in amp-hours can be doubled for the proper amp-hour rating of the battery bank, either the trucks stock batteries or additional batteries you add. Keep in mind that deeply discharging will shorten their life. Most group 27 deep cycle batteries are 105 Amp-hours which will give you a safe 50-60 amp-hours of discharge. If your combined draw were 10A (just guessing) you could run your heater for say, 6 hours and still know that your truck would start. AGM (absorbed glass mat) batteries have a bit more room to discharge than flooded. What kills batteries is leaving them in a discharged state so be sure to drive the truck long enough to bring the state-of-charge up to at least 90%.

Your situation is no different than the average RVer that uses a lot of amp-hours and then has to choose the best way to charge, usually with a generator, solar, or driving a long time. If you don't bring the batteries to 100% charge after a 50% depletion then the math above will not work. You have to start with how full the batteries are to calculate correctly.

Even with an additional battery bank, no matter how big, recharging is the key to reliability or you will still have dead batteries, just more of them.