150A alternator enough for portable A/C unit?

ions82

Member
I am planning to use a portable A/C unit in my van to help keep it cool in the summer. It is rated for a max power draw of around 1,100 watts. If I figured it correctly, that's around 78 amps at 14 volts. It will be running on a 3,000W inverter (which is around 87% efficient.) Would a 150A alternator be sufficient for such a setup? Should I plan to employ extra batteries to help soften the draw as it cycles on and off? I'll also be running a small stereo system from the inverter. Would a 200A alternator be a better option? Or is it inefficient to run a larger-than-necessary alternator?
 

john61ct

Active member
It is crazy expensive and inefficient to sit there running your propulsion engine to power A/C.

Probably cheaper to rent a motel room.

Travel to cooler places.

Or buy a genset.
 

BrennWagon

He’s just this guy, you know?
If you’re planning on running the a/c unit while driving, you may want to consider a higher output or secondary alternator depending on the other loads that your powering, regardless the addition of an aux battery would be a good idea.

If you’re planning on using the a/c while parked/camping you’ll need a huge battery pack and it’s becoming more feasible but still very expensive to implement
 

john61ct

Active member
Figure an extra 100Ah per hour of aircon.

And good luck recharging the bank at the same time as running the aircon.

Few of those portable units are even effective, even the 2-hose ones, forget the singlets.
 

Midwestdrifter

Engineer In Residence
The 150A unit can supply about 80 amps extra at cruising speed. You would be running right up against the alts limit. It would probably work though. If you have the factory Aux AC with roof mounted condenser, you may have only 70A extra capacity.

As mentioned idling is a loosing proposition. If you need to Idle for extended AC times, get a generator.
 

Geriakt

2017 View 24J
You should watch this video before you attempt your plan. You should consult a proper engineer. Your small alternator can not put out what you want to do. Pulling that many DC amps will burn up your small alternator. The proper way is draw from a large battery bank and then use a DC to DC charger from your alternator to replenish your AH at a much lower amp draw like 15-25 amps.
A split AC unit is much more efficient and can draw only 400 watts. A roof top RV AC unit 13500 btu will pull 1600 watts

There are many Van life people using Tesla modules to power 5000 btu window AC units. Some even split the window unit. I have two Tesla modules in my RV and do run my AC off of them, but then again I invested $5000 to do so. I am almost ready to delete my gen set.
https://youtu.be/jgoIocPgOug
 

ions82

Member
The portable A/C unit would only be used while driving. If stopped, I'd have a small generator running or be using shore power. I'd never be letting the engine idle for any length of time.

All that said, it seems like it would still be right at the limit of what a 150A would be comfortable with. Then again, I have no idea what the rest f the van draws for current. I imagine headlights require a fair bit of juice.
 

Midwestdrifter

Engineer In Residence
The engine needs about 20A to run its bits. Add 10A for the AC blower, 10A for the lights, another 10-12 for the radiator Aux fan. That gives you 50+20 for other overhead. The factory minimum 90A unit is capable of running everything on the van at idle, with a bit to spare.
 

marklg

Well-known member
Where are you driving? I am in the desert southwest, but the front AC is still enough to cool the back while driving. While parked I do use the rear AC with the genset, or plug in. This summer we just went places where it was cooler and the AC wasn't needed.

I have 400Ah of LiFePO4s but don't run the AC off them. Any place in the 70s F, cracking the openable windows and exhausting air via the roof fan makes us comfortable. I'm a safety fanatic and putting the Tesla batteries in the vehicle where I sleep is not for me.

Regards,

Mark
 

john61ct

Active member
I'm a safety fanatic and putting the Tesla batteries in the vehicle where I sleep is not for me.
Nothing fanatical about that, anyone who thinks that's OK is an idiot.

IMO

LFP & LTO fine NP, but not any other LI chemistry afaik
 

ions82

Member
Where are you driving? I am in the desert southwest, but the front AC is still enough to cool the back while driving. While parked I do use the rear AC with the genset, or plug in. This summer we just went places where it was cooler and the AC wasn't needed.
I live in Albuquerque but will be traveling about the U.S. I'll have the van fairly well insulated, and I'll also have my two dogs with me. They are the reason why I was planning to add another A/C, but perhaps I would be better off just making sure the factory A/C is in tip-top shape. As of now, it needs to be charged/serviced. I bet the cabin filter is clogged with dust, too (I have a replacement to install.)

Perhaps I mislead myself in thinking that I even need a secondary AC unit while driving. I could always reserve the portable unit for the occasion we are camping out near a power source. From what I'm reading, it sounds like powering even the smallest A/C unit would tax the alternator. I have a newfound love in my Sprinter van. I certainly don't want to abuse it.
 

220629

Well-known member
I find the OEM front A/C to be marginal at best for cooling the back of my 140 2500HC. It has windows all around and no added insulation.

I have found that a 120 volt fan powered by a 300 watt inverter helps move air into the back. A household 120 volt extension cord makes it easy to supply the fan from the inverter.

This is similar to what we use.
https://www.walmart.com/ip/Honeywell-TurboForce-Power-3-Speed-Air-Circulator-HT-900-Black/10980207

We have a 12 volt double fan unit which hangs off the driver seat headrest. Those fans are ok when we have people seated in the second row only. They do nothing for those seated further back.

:cheers: vic
 

autostaretx

Erratic Member
Your needs are why MB (and 3rd party vendors) offer a roof-top AC to handle the cargo/passenger area.
The MB unit has a 2nd compressor attached to the engine, and only uses electrical power (30 amps) to run the fans.
The crankshaft pulley gets an extra V-belt pulley to drive it.

Many people doing conversions *remove* the roof-top AC, so you might be able to pick one up very inexpensively (free for pick-up).
The only holes in the roof were two 2 inch round holes for the fluid lines to pass through.

People also "simply" add a 2nd alternator to gain up to 250 amps of extra power. The crankshaft pulley gets the same "extra level" that the AC compressor would have used.

You can also change out your existing alternator to a 150 amp or 200 amp unit. MB sold the 150 as an option during the T1N years, and some members have fitted the 200 amp.

--dick
p.s. the big advantage to a 120vac AC is that you can run it with shore power when not driving.
 

marklg

Well-known member
I find the OEM front A/C to be marginal at best for cooling the back of my 140 2500HC. It has windows all around and no added insulation.

I have found that a 120 volt fan powered by a 300 watt inverter helps move air into the back. A household 120 volt extension cord makes it easy to supply the fan from the inverter.

This is similar to what we use.
https://www.walmart.com/ip/Honeywell-TurboForce-Power-3-Speed-Air-Circulator-HT-900-Black/10980207

We have a 12 volt double fan unit which hangs off the driver seat headrest. Those fans are ok when we have people seated in the second row only. They do nothing for those seated further back.

:cheers: vic
Ours has very dark windows in back and insulation. At idle, the AC is not so good, but while driving, I've sat in the back for long periods and it has been OK. I did make sure the AC up front was fully charged. That made a big difference.

Regards,

Mark
 

ions82

Member
Once again, the helpful knowledge so kindly shared in this forum has helped prevent me from making missteps. I think I will NOT try to run an A/C unit from the alternator and instead just focus on making sure the factory system is in good form. I will still run an inverter to provide A/C power, but it will only be a small one that will probably never even see 500 watts. I'll bring the portable A/C along in case I can run it off shore power while parked. It's nice having so much space in a 158".
 

nutterbutter

2004 LTV Free Spirit T1N
My rv is based on a Long/Tall with some insulation, but not great insulation. Driving across Nevada/Utah in Sept a couple years ago, the AC on max kept us reasonably cool even though the van said it was over 110 outside. I noticed there was still some perspiration in the seat when I got up though.

In the back, my bag on the ground had some chocolate. The floor is carpeted, but the chocolate totally melted. Away from the front it does get hot.

You have to remember to keep pressing the recirculation air button. For some odd Mercedes reason, they have it reset automatically after a time. Makes a big difference when it is hot out.

When I have the dog and it's warm out, but not super hot, I sometimes put some ice in a large bucket in the middle of the floor when parked. It does make a difference and when he's hot, he moves to sit next to the bucket. (After a long drive, the transmission also dumps a LOT of heat back into the van when parked). There's lots of free ice in the hotel! When it's real hot I just run the generator and AC.
 

owner

Oz '03 316CDI LWB ex-Ambo Patient Transport
I have run a 800W rooftop AC run through an inverter off my stock 150A alternator. On hot days (35C+ which is when I use it to compliment my dash AC) the alternator struggles to keep up even at cruising speed. The main battery voltage eventually dips into the high 11V's which is not good. I guess this happens when the alternator starts glowing red hot. I have ordered a new Bosch 200A alt and will have that fitted in time for summer so hopefully that is good enough.

Im not able to measure the 12V current draw from the alternator direcrly, but when I switch over to my LFP bank to power it, the AC pulls around 90A at 12.0V
 
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