Best battery for buffering rooftop A/C

W

wlderdude

Member
So I'm starting to convert my 2006 T1N Sprinter into the ultimate family road trip vehicle. I've got benches installed to travel 7 of us and beds are going in to sleep 5.

We live in Texas. One of the hard requirements handed down from the wife is the vehicle is that the vehicle must have rear A/C. I know most people converting vans don't need to get cold air back to a 3rd row, but there will be times when the dash A/C won't be enough. A/C that runs off of shore power is also needed.

I'm not naive enough to think we can run the A/C off of batteries or solar panels. I have sourced a 250 amp alternator that should have the juice to power the Coleman Mach 8 I picked up recently. Running it as an auxiliary alternator would be ideal, but I can't find the resources to figure that out. So everything needs to run off the 1 alternator.

When running at reasonable rpm, the 250 amp alternator should provide enough wattage to keep the vehicle running, charge the battery, and run the air conditioning. I'm not so sure about idle, though. It seems to me relying on the vehicle starting battery to buffer the inevitable periods of idling would not be smart. I figure I need a house battery anyways.

So my question is what kind of battery would be appropriate to use?

It seems that AGM batteries are popular, but I don't know if hooking it up to a high wattage alternator would be wise. It'd be nice to be able to mount them inside.
Would some golf cart batteries or a marine deep cycle work best? I'm sure I could figure out how to mount them under the vehicle, but maintiang them would be a pain. Does it need to match the starting battery in the T1N?

Do I need solar panels to top off the charge if the alternator can't keep the charge topped off? I don't plan to dry camp more than 1 night at a time and don't really want to mess with solar panels.

Any other thoughts or recommendations?

Thank you.
 

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autostaretx

autostaretx

Erratic Member
If you can rig a "high idle" for the engine, the alternator should be able to handle the load ... the batteries would hardly notice it.
1200 rpm would probably be adequate. Check the alternator's speed/power curve.

There's another current thread with a (controversial) add-on to the accelerator pedal that flips up to press it a bit.
The "controversy" is how you keep it (or Murphys Law) from accidentally engaging high idle when you really want to drop to low idle when driving.

The Coleman takes 1550 watts in "desert cooling" mode, but can peak to 58 amps (at 120vac: over 500 amps at 12v) if the compressor locks up. 1550 watts equates to 130 amps at 12vdc, let's call that 150 amps to allow for losses.

If you really want that to come from a battery (even on a short burst) I *think* you're going to need more than one battery in parallel to achieve that current draw rate. A single battery would sag in voltage quite a bit.
This might even be a case where a "starting" battery (short duration high-current draws) might do better than a typical "deep cycle" (moderate draw) battery.

--dick :2cents:
 
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hein

hein

Van Guru
wlderdude said:
So I'm starting to convert my 2006 T1N Sprinter into the ultimate family road trip vehicle. I've got benches installed to travel 7 of us and beds are going in to sleep 5.

We live in Texas. One of the hard requirements handed down from the wife is the vehicle is that the vehicle must have rear A/C. I know most people converting vans don't need to get cold air back to a 3rd row, but there will be times when the dash A/C won't be enough. A/C that runs off of shore power is also needed.

I'm not naive enough to think we can run the A/C off of batteries or solar panels. I have sourced a 250 amp alternator that should have the juice to power the Coleman Mach 8 I picked up recently. Running it as an auxiliary alternator would be ideal, but I can't find the resources to figure that out. So everything needs to run off the 1 alternator.

When running at reasonable rpm, the 250 amp alternator should provide enough wattage to keep the vehicle running, charge the battery, and run the air conditioning. I'm not so sure about idle, though. It seems to me relying on the vehicle starting battery to buffer the inevitable periods of idling would not be smart. I figure I need a house battery anyways.

So my question is what kind of battery would be appropriate to use?

It seems that AGM batteries are popular, but I don't know if hooking it up to a high wattage alternator would be wise. It'd be nice to be able to mount them inside.
Would some golf cart batteries or a marine deep cycle work best? I'm sure I could figure out how to mount them under the vehicle, but maintiang them would be a pain. Does it need to match the starting battery in the T1N?

Do I need solar panels to top off the charge if the alternator can't keep the charge topped off? I don't plan to dry camp more than 1 night at a time and don't really want to mess with solar panels.

Any other thoughts or recommendations?

Thank you.
Click to expand...
I grew up in Kansas and have spent plenty of time in Texas so I know the drill.

Which Mach 8 did you purchase? We have the 9000 BTU on our van with 500Ah battery AGM battery bank and Magnum 2800 watt inverter. The system starts and runs the AC just fine but might be a stretch all night with 7 bodies aboard. We would check into an RV park and plug into shore power if we needed that. We have very good 3M Thinsulate(TM) insulation so actually can keep the van cool throughout with the cab air while driving. Just need to run the roof top AC a while when we pull over to sleep for the night. Here is the amp draw on the 12V side with the AC running:



You might consider Battleborn LiFEPO4 batteries which will let you run longer without running the engine. You should be able to draw at least half of the current off the alternator on high idle but remember all that heat from the engine will then be percolating into the living space so may actually defeat the purpose. I would consider a small remote generator if that was necessary. That could get some frowns from your neighbors in a campsite. No problem at a rest stop with diesel trucks running their gen-sets nearby.

I would be happy to discuss at length in a phone call.

All the best,
Hein
54l 49O 5O98

P.S. I would seriously consider mounting the AGM's and even LiFEPO4s under the van for stability and safety for your precious cargo. There is no maintenance you can do on either so accessibility is not an issue. And get familiar with hydraulically crimping lugs onto 4/0 welding cable.
 
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J

john61ct

Active member
You need a strong battery bank anyway. But just "buffering" the alt or genny+charger output to the aircon is NBD, anything will do. But you **must ensure the input is more than keeping up with the total load demands.

Matching Starter or even better making that all one big bank helps with redundancy.
 
marklg

marklg

Well-known member
Note that you should switch both hot and neutral for AC power sources. For generators and shore power, the neutral is connected to ground at the source, and often has a Ground Fault Interrupter. If the inverter or generator connects the neutral to ground somewhere else, the first GFI will pop as soon as you plug into shore power.

So, both hot and neutral should be switched and the inverter set to connect neutral to ground at itself. Connecting neutral to ground is important for safety so there is not a somewhat hot conductor open to electrocute someone. I'm not sure if all inverters can do that, but hopefully they include a GFI to detect if there is a leakage to ground and provide equivalent safety.

Regards,

Mark
 
W

wlderdude

Member
marklg said:
Note that you should switch both hot and neutral for AC power sources. For generators and shore power, the neutral is connected to ground at the source, and often has a Ground Fault Interrupter. If the inverter or generator connects the neutral to ground somewhere else, the first GFI will pop as soon as you plug into shore power.

So, both hot and neutral should be switched and the inverter set to connect neutral to ground at itself. Connecting neutral to ground is important for safety so there is not a somewhat hot conductor open to electrocute someone. I'm not sure if all inverters can do that, but hopefully they include a GFI to detect if there is a leakage to ground and provide equivalent safety.

Regards,

Mark
Click to expand...
That makes sense and is good to know. I'll be sure to use DPDT relays to switch both hot and nuetral wires. Thank you for the advice.

Are there any primers or guides you would recommend?
 
marklg

marklg

Well-known member
wlderdude said:
That makes sense and is good to know. I'll be sure to use DPDT relays to switch both hot and nuetral wires. Thank you for the advice.

Are there any primers or guides you would recommend?
Click to expand...
These threads:
https://sprinter-source.com/forum/showthread.php?t=65974
https://sprinter-source.com/forum/showthread.php?t=68874

and the sticky one at the top of this forum:

https://sprinter-source.com/forum/showthread.php?t=51232

They link to lots of other documents to read.

There are also some things there not to do.

If you search these forums for electrical terms, you will find lots of useful info.

Hope all this is a help.

Regards,

Mark
 
H

HarryN

Well-known member
In case it is interesting, we build drop in electrical setups exactly for your application.

The core starting point of my business was based on a system that can run air conditioning like this for various time periods by combining power from 1 or 2 alternators, grid, generator, and solar - as available - and run the auxiliary air conditioners.

The systems are modular and the a/c run time various by model from "buffer - about 1 hr" to 8 hrs.

Some approaches are a lot easier to pull off than others, but the more it is approached at a "system level", the more likely you are to achieve success.

We have 2 such systems in progress for customers right now. One is a system similar to your general needs description that will go into a sprinter in Louisiana, and another for here in CA that can do the buffering + 3 hrs engine off capable for a Promaster.

Both are based on slight variations of our 2x2 product.

Feel free to look at the web store site and use the concepts as you like, or we can save you some time by providing a completed and tested unit - shipped to your door.

The store site has an annoying feature that requires you to click on the photo and wait a few seconds to follow arrows to the next photo, and you have to click on "more info" to get all of the specs.

Thanks to encouragement from Dave Orton / Graphite Dave - we also offer some more "conventional level" conversion van versions. (the 1x1)

Feel free to contact me any time.

Harry

www.squareup.com/store/wirlnet-com
 
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