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BRINGING IT ALL TOGETHER.... A's, G's & E's


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Air Conditioning idea - could it work?

Space Truckin
Space Truckin


Number of posts : 1267
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Post by Space Truckin Tue Apr 19, 2022 9:39 pm

Interesting.... study
AzDon
AzDon


Number of posts : 564
Location : Lake Havasu Az
Age : 66
Registration date : 2014-01-20

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Post by AzDon Mon Apr 25, 2022 2:43 pm

So the 5k BTU unit I'm considering needs 115v @ 4 amps/480 watts......
The math suggests I'd need 40 amps @12v to run it but also a momentary surge amperage availability of 80-100 amps.....
I guess my overall question is......
How big will a pure sine wave inverter need to be to handle these input-output specs?
My additional alternator can provide 105 amps running and the extra battery can produce more.... I just need inverter sizing info to get the AC the power it needs
AzDon
AzDon


Number of posts : 564
Location : Lake Havasu Az
Age : 66
Registration date : 2014-01-20

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Post by AzDon Sun Jun 12, 2022 3:06 pm

So I found another calculator...... Amps to watts!

https://www.rapidtables.com/calc/electric/Amp_to_Watt_Calculator.html

If I'm reading it correctly, each of my 105 Amp CS alternators output 1260 watts (x2=2520 amps)

One of the vids I watched implied that a 5k BTU 120VAC window air rated a 400 watts will require about 500 watts through an inverter to run and 800-1000 watts for startup surge
chiefcrewdog
chiefcrewdog


Number of posts : 17
Location : Vail, AZ
Registration date : 2017-11-29

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Post by chiefcrewdog Tue Jun 21, 2022 10:30 am

AzDon wrote:So I found another calculator...... Amps to watts!

https://www.rapidtables.com/calc/electric/Amp_to_Watt_Calculator.html

If I'm reading it correctly, each of my 105 Amp CS alternators output 1260 watts (x2=2520 amps)

One of the vids I watched implied that a 5k BTU 120VAC window air rated a 400 watts will require about 500 watts through an inverter to run and 800-1000 watts for startup surge

On calculating your wattage for your alternators, use 14.2 volts instead of 12v, since this is the typical regulated voltage going to your battery when the engine is running. 1491 watts each.  Next, as far as running on batteries, the voltage to calculate amp load will have to be based on 12-12.5 volts the batteries can supply and there is a drawdown to consider.  IE how long can the batteries alone supply the required voltage given the amp load?  Calculated in terms of amp hours.  For example, a 12V lithium battery with a capacity of 100Ah can deliver 100A to a 12-volt device for one hour.  All electric AC works great in a Tesla but they have a massive and very efficient battery bank, capable of a lot of Ah (350V 230 Ah).  I'm thinking you'd need several deep-cycle batteries (4 or more) to get any sort of usable amp hour load and even then, you will be limited in how long it could run for on batteries alone.  Dual alt's and a battery bank to soak up transient loads, could get the job done with the engine running but it needs to be science'd out and I seriously doubt you could run all night on batteries.  Maybe an hour or two before you'd flag your battery bank, but I haven't tried calculating it all out..  Longer run time with more batteries BUT more time required and alternator amperage to recharge as you add batteries, so that need to be figured out too.  AND I'd keep the system isolated from your start battery.  Best bet would be to utilize modern battery technology from current electric cars.  The batteries have better efficiency, charge and discharge, than lead acid.  You can build battery packs using components sourced online but they aren't inexpensive.  As for sizing the inverter, I'd see what the instant load is on 120 VAC wall power using an inductive amp meter (clamps around the cord). Measure startup spike at least 3 times (wait an appropriate amount of time in between for the system to normalize) and average the result.  Energy conversion using an inverter costs battery efficiency.  There is no free lunch.  Turning alternators to power an inverter running an ac unit will draw down engine power.  Probably more than a compressor mounted to the engine will.  You may not feel it as much as the onset will be less noticeable than a compressor clutch cycling but it will take a fair amount of HP to turn those high amp alt's.  As I said above, the process of inverting DC to AC itself uses power and there is heat generated (why there are cooling fins and fans) and this heat is going into the area you're trying to cool unless you mount the inverter outside and that can be problematic unless the unit is weather proof and made to work in a high ambient heat environment.  FWIW: RVs tend to mount the inverters in the storage compartments with adequate ventilation.  All things to consider.  For your inverter needs, be sure to give yourself at least 30% added capacity above the calculated worst case amp draw.  And size all wiring to handle the rated loads with the same sort of excess capacity.  50% more would be better.  Better yet, think of it this way.  The amp rating on the inverter is a max rating.  BUT I guarantee you there is a much lower continuous duty cycle rating that you should size to.  My MIG welder can weld 1/4" steel but has a much shorter duty cycle when doing so.  I can't just wail away at max current.  The machine will go into overload and shut down until it cools down.  Inverters will have this same sort of limitation.  All electronic items do.

https://www.mkbattery.com/blog/understanding-battery-amp-hours
Take a look at this link to help get your head around Ah and added info regarding heat generation in the battery from rapid charge and discharge.  This heat issue also cannot be ignored.  It directly affects the performance of the battery.
AzDon
AzDon


Number of posts : 564
Location : Lake Havasu Az
Age : 66
Registration date : 2014-01-20

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Post by AzDon Tue Jun 21, 2022 10:20 pm

Wow!.... Thanks Dave!...I was not believing that I could run the window AC on batteries without the engine running.... I was just considering that I'd have a system that could plug to shore power when parked.
The AC probably requires a 2000 watt inverter and I hadn't really considered it's heating potential.... perhaps I could mount it next to the condenser air intake so that the condenser fan would blow that heat through and out the exhaust duct (?)...
I do have one alternator and battery wired independently and isolated, but able to be tied to the pair that run the van with a battery switch.....I'm also thinking of building a 12v ice chest AC that pumps icewater through a trans cooler sandwiched with a fan.... basically a mini-split using icewater instead of a compressor/condenser.....I figured I'll build that first to see if it's viable for any length of time with the engine running, also knowing I could run it for a while off the isolated battery alone for off-grid ops...... I also have the factory Harrison AC compressor mounted on the engine and two or three different evap setups I could use, but the other required hardware is ugly and hogs space and would add heat to the engine bay....
In a perfect world, I would be able to create a full array of rooftop heat exchanger/extractors that aren't ugly and vent the engine box through the roof while I'm at it because heat rises..... Something that looks like a cross between a vista cruiser roof and a World of Outlaws wing..... No can do though because my garage door is only seven feet high.....I'm on body work right now which is a bit mind numbing, so I consider this stuff for mental exercise....

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chiefcrewdog
chiefcrewdog


Number of posts : 17
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Registration date : 2017-11-29

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Post by chiefcrewdog Wed Jun 22, 2022 8:18 am

I believe you can probably run one from batteries for some length of time but like I said, a rather short amount unless a sizeable battery pack with good-great Ah performance.  

A good friend has a Tesla and running the AC (or heat) parked or otherwise, takes a small fraction of total battery life.  something like 3-4%  This could be a factor if on a long run but around town and general commute distances is nothing.  So like I said, AC on batteries is completely doable.  Its been done.  

On to your other ideas.  The cold box heat exchanger is regularly used by the Street Outlaw guys to cool the inlet charge instead of running large intercoolers.  Tank under the rear decklid and exchanger under the cowl typically.  Its why the intakes are reversed toward the back on some of the cars  The turbos that they use are huge heat sources.  So, again, a solid idea that could produce good to great results.  Just need to try it and work the bugs.  Much as I suck at it, math is your friend on all of these exercises, so you don't spend money you don't have to.  Thermodynamics (like electrical properties we've been discussing) are well understood and all the formulas exist for the taking.  Just have to get familiar and avail yourself of them.

Venting the inverter through the AC inlet could work but would drop the efficiency (reduce the BTU/cooling) of by some amount.  Maybe a factor, maybe not.  But I'd guess the net net, its the same as the heat source residing in the cab airspace, with the exception of not feeling the localized heat near the inverter.  The heat is still going into the inlet side...

Having belly mounted heat exchangers is not a problem.  I'm considering a traditional AC unit with belly mounted exchanger.  I may try using a rear AC unit from say an Astrovan, in addition to a streetrod style under-dash unit  You'd just need ducting to get air in and out.  Consider this.  Our vans have a huge negative pressure zone behind them when running down the road.  That is why we smell exhaust if the door seals are bad and why any oil leaks are readily apparent.  Just look at the rear doors!  The low pressure pulls air into the back of the van.  A relatively small and inconspicuous slot looking outlet in the rear bumper area would likely scavenge any duct placed there due to the low pressure.  Think of this in terms of the famous WWII North American Aviation P51 Mustang.  It used a belly mounted radiator of modest frontal area to cool that monster turbo/supercharged Merlin engine.  Compound supercharging and the resulting HP makes a ton of heat.  The (even smaller sized) slot at the rear had a variable pitch ramp to tune the efficiency at various speeds and was said to provide a minimal amount of thrust at higher speeds from the heat expansion of the slot exit!  We can grab that page from their book of learning and make it work for our cooling needs.  Put a t-stat controlled high-efficiency fan on the backside of the cooler(s) for when sitting still.  Food for thought!

EDIT:
https://www.forestriverforums.com/forums/f218/how-much-heat-does-a-3000-watt-inverter-give-off-174709.html

While he doesn't answer the question of how much heat is produced, the insights given by Herk7769 seem to be right and underscores challenges with using larger inverters on batteries OR alternators. And like I said before, there will be duty cycle to consider.
AzDon
AzDon


Number of posts : 564
Location : Lake Havasu Az
Age : 66
Registration date : 2014-01-20

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Post by AzDon Wed Jun 22, 2022 1:16 pm

If you look at my build thread in "Members Showcase", there are pics of four slots I cut through the floor into the chassis channels to drop "stress bridge" pieces in to bolt the engine and trans cross members to.... Those channels are open at the very front and very back of the van at the bumper brackets.....If I un-block the front openings, air would be force-fed through those channels and I could use them as exhaust venturis.....
I also have an opening over the fuel tank for pump servicing that I could use as an exhaust port for the AC...
One Youtube video I watched suggests that the "portable" free standing AC units are less efficient because they draw cooled room air through the condenser to the 5 inch exhaust, resulting in negative pressure in the room that can only be alleviated by allowing outside air in that isn't cooled......This is a hard buy-in for me, because using cooled air for the condenser should provide better cooling to the condenser than raw outside air.....
All of the ducting required could suck up all of my under-bed space and I could end up with stuff that doesn't really work that great...

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AzDon
AzDon


Number of posts : 564
Location : Lake Havasu Az
Age : 66
Registration date : 2014-01-20

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Post by AzDon Wed Jun 22, 2022 1:29 pm

Another idea I've considered is to have the factory heater dual plumbed to both an engine coolant heat exchanger AND the ice chest loop so that you could switch the hose loop between hot and cold water..... Maybe actually have a small radiator that lays in the bottom of the ice chest so that part of the loop could use antifreeze and make a heat exchanger for the hot side unnecessary......
After crossing swords with a local plumbing company last week (I won!) I've decided that I'm going to buy some supplies and learn to proficiently solder copper and building some of this stuff would be great practice!

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