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Old 12-03-2008, 02:15 PM   #11
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Not to drag off topic, but what does your voltage read while the A/C is running at full blast after startup and what inverter are you running?
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Old 12-03-2008, 07:47 PM   #12
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Quote:
Originally Posted by Ethereal
Maybe they felt less responsible since we brought "our own" inverter, but that still doesn't account for their blase' attitude that the sine wave units they use won't start their A/C's either.
Not sure I understand that. Our inverter both the originally spec'd model and our current model are sine wave inverters.

We are using the Xantrex P2000 and it starts the AC just fine with or without the gen. This is the inverter that SMB TX has used in the past and sounds like they will continue to use in the future.

Providing your own equipment does throw an additional difficulty factor into a build like this. The items we provided were peripheral equipment or equipment identical to what they use.
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Old 12-03-2008, 09:34 PM   #13
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Originally Posted by daveb
Not to drag off topic, but what does your voltage read while the A/C is running at full blast after startup and what inverter are you running?
DaveB.
The inverter is the MagnaSine 2812. The running voltage was 118-119.
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Old 12-03-2008, 09:39 PM   #14
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Originally Posted by Greg In Austin
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Originally Posted by Ethereal
Maybe they felt less responsible since we brought "our own" inverter, but that still doesn't account for their blase' attitude that the sine wave units they use won't start their A/C's either.
We are using the Xantrex P2000 and it starts the AC just fine with or without the gen. This is the inverter that SMB TX has used in the past and sounds like they will continue to use in the future.
It was discussed with both Paul and Kevin at length. I'm sure I understood them correctly because they even acknowledged the irony that the cheap-and-dirty MSW units were the only ones that would start the A/C.

Maybe they've changed their standard roof A/C unit since your build. We have a Carrier Air V Low-profile 13,500 BTU.
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Old 12-03-2008, 10:32 PM   #15
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Quote:
Originally Posted by daveb
Not to drag off topic, but what does your voltage read while the A/C is running at full blast after startup and what inverter are you running?
DaveB.
Is it really the voltage that is the concern for the 'startup' of the AC? or is it the amperage?

When we are running our AC on our generator it actually needs help from the inverter and batteries to "start" the AC.

...and that is where the importance of the inverter came in for us. The inverter had to be smart enough to power share and use the batteries on as needed.
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Old 12-04-2008, 06:46 PM   #16
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Is it really the voltage that is the concern for the 'startup' of the AC? or is it the amperage?

When we are running our AC on our generator it actually needs help from the inverter and batteries to "start" the AC.

...and that is where the importance of the inverter came in for us. The inverter had to be smart enough to power share and use the batteries on as needed.

Maybe I’m missing something here, but a constant Low voltage will damage the A/C and shorten its life. High amperage loads usually pulls down the voltage if the supply is close to operating at 100%. Amperage can trip the breaker just like the low/high voltage set points can trip the inverter. The inverter can handle only what it’s designed to and many are super sensitive to voltage irregularities. I would think a Danhard or Starcool A/C that is manufactured to run off DC voltage is another situation. In your setup Greg it sounds like you needed a little boost to get over the startup hump (and that hump can be substantial) even though you’re still running the generator way less than 100% to keep the A/C going. Your inverter acts like the capacitor he installed; adds just enough to get over the hump. My guess is you didn’t want to haul a big generator along with you if the inverter could add the necessary boost. The roof mount A/C if I'm not mistaken (or am I?) is similar to a household unit that is made to run off typical AC utility voltages where it would be supplied from a 20 or 30 amp standard panel breaker. Who would want to run down the road with the generator running? Even if the roof top A/C could run off AC or DC I would not see the advantage to run it through the inverter if DC is available unless the AC efficiency factor was enough to off set the draw of the inverter itself.

I too would be upset if I ordered the correct size inverter to handle the load and found out it was unable to. Even worse pull the inverter out and replace it with a larger one and find out a cheap fix is out there. I just figure that SMB is not that up and up on roof mounted type air conditioners like many typical RV manufactures. Maybe I’m wrong on this but before the Sprinter did they even work with roof mounted A/C’s?

The only thing I would worry about is if the alternator does in fact put out enough to keep everything inside the van going while still providing additional amperage to keep the batteries up. So if you start with a house battery that's at 60% and turn on headlights, wipers, stereo amps, the stock A/C and the roof A/C, you still want to see a positive flow to the house battery say 3 or 4 amps minimum while driving. More is better.
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Old 12-04-2008, 06:58 PM   #17
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You are correct on our setup.... the generator just needs a little extra amperage to get over the startup needs, and then the gen just idles to run the AC.

We can run our AC off batteries and inverter for a couple of hours with no issues, other than pulling the batteries down.

On our DC trip we tested running the Danhard while driving and turning the van AC off. This worked fine and did not pull the batteries down. We do have a high output alternator.

I think they may put a rooftop AC unit on a lot of Sprrinters.

Why bring your own inverter to the party at all, let SMB know what you want, and let them design the system as a solution; that part they know how to do because they have done it in the past. By introducing a different inverter (assuming it was not the same inverter that they would provide), you put a new variable into the equation that they already solved.

We fell into the same trap, wanting to go with the newer smarter design of the RS2000, and yet it could not do what was needed. When we went back to the SMB-understood P2000 everything was fine.
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Old 12-04-2008, 07:38 PM   #18
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Why bring your own inverter to the party at all(?)
The inverter we used includes full house power management--it will run the generator as necessary to charge up the batteries, then shut it down until it is needed again. (Kinda like a thermostat, but for battery charge instead of temperature.) It can also be set with a lockout on generator running for "quiet time" at night.
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introducing a different inverter (assuming it was not the same inverter that they would provide), you put a new variable into the equation that they already solved.
I do hate to belabor the point, but Paul and Kevin both explained, at some length, that their standard sine-wave units can't start a roof A/C either. I can't imagine why they would have made that up.
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Old 12-04-2008, 08:13 PM   #19
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I think I would still give them the problem and let them work a solution.
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Old 12-04-2008, 09:43 PM   #20
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I think I would still give them the problem and let them work a solution.
I really don't understand what you mean. The following is an exhaustive list of the options they were able to offer:

a.) Use a modified-square-wave inverter;
b.) Run the A/C on generator or shore power;
c.) Sweat profusely.

None of these were acceptable, nor were they "solutions." They concluded that it was impossible to run the A/C from a sine wave inverter; and they were consequently done "working."

What do you think they could/would have done? And why do you think they would have done anything, given their foregone conclusion that the task was impossible?
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