Comment on this inverter please...

bevans6 · June 06, 2010, 08:40:26 AM

I've been looking at this inverter for a while now. Primary application will be powering the roof AC while on the road, since I don't want to run the generator (it's a gas generator, a Yamaha 3000 inverter model, and if I plan to run it for more than a few minutes I like to remove it from it's home in the old OTR AC compartment and put it on the ground outside the bus).

so this is the inverter; http://www.theinverterstore.com/the-inverter-store-product.php?model=pwri300024s-top-250#

24 volt, 3000 watt, remote on/off, pure sine wave, direct connect AC output, has CE approval with I think is recognized as equivalent by CSA.

I would plan to connect it via the old AC condenser fan solenoid and relay (fused at 105 amps), set up so that it could only connect when the alternator is charging. That way it can't load down the start batteries or operate accidentally when the bus is not running. I would route the 120 volt AC to the roof AC unit and maybe the fridge and an accessory outlet for running a charger or something, via a transfer switch set up for house AC power priority, so that as long as there is power from a pedestal or the generator, the transfer switch will send that to the load. If there is no house ac power AND there is inverter power, the switch will send inverter power to the load.

I see my actual load being 1800 watts or less (15K BTU Briskaire) , except when starting the motors, so actual power consumption should be under 2000 watts virtually all the time, or call it 73 amps at 27.5 VDC, which is what the alternator is set at.

Anybody see anything wrong with this plan?

thanks, Brian

BG6 · June 06, 2010, 10:33:47 AM

No load, it draws an AMP AND A HALF???

I suggest that you contact the company and verify whether that's no-load-idle or no-load-switched-off.

4500 watts intermittent should let you start the aircon without worry.

Your 105 amp relay isn't enough for the hot lead to the inverter (do the math -- divide 4500 watts by 24 volts and you get the amps). That's the bad news. The good news is that, if the no-load-switched-off standby current is low enough (under 1/4 amp), you can use that relay on the remote switch circuit and just leave the inverter hooked up all the time.

I suggest that you check with semi and RV shops and salvage places. There is enough 24V equipment running around that someone may have a good inverter, but isn't wildly popular so they may be eager to find a buyer.

bevans6 · June 06, 2010, 11:09:17 AM

Pretty sure that's no load idle, but I will investigate. Struck me as high, too, but I haven't compared to a lot of other units yet.

My thinking on the load is that since the load (the roof-top AC)is fused at 20 amps AC, the max wattage into it is 2400, or 87 amps at 27.5, which is about the same as the motor for the condensor fan. It's breaker is 105 amps. Basically the inverter is well oversized for the load, which isn't always a bad thing. I just will never use it's capability in this installation.

The thing is, it's kind of hard to find a pure sine inverter in the 2K to 3K wattage range with any approvals at all, no charger, and with a direct connect AC output. Those are the specific things I am looking for, although the remote control is very nice to have. I haven't found a lot of them for under a grand...

Brian

BG6 · June 06, 2010, 12:09:13 PM

Quote from: bevans6 on June 06, 2010, 11:09:17 AM

My thinking on the load is that since the load (the roof-top AC)is fused at 20 amps AC, the max wattage into it is 2400, or 87 amps at 27.5, which is about the same as the motor for the condensor fan. It's breaker is 105 amps. Basically the inverter is well oversized for the load, which isn't always a bad thing. I just will never use it's capability in this installation.

I STRONGLY URGE that you plan for full capacity of any electrical circuit (plus 20% for loss). I've never seen anyone looking at a smoldering pile of junk and say "I'm sure glad I used that small-gauge wire!"

Another thought, did you take out the factory aircon compressor? If so, you can mount an AC generator (these can be found for pennies with dead gas engines) where the aircon was, drive it from the same belts, and have SIX KILOWATTS OF AC anytime you have your engine running.

BTW, you probably already have 4 or 5 KW of DC . . .my TMC has a 270 amp alternator, multiply by 24 volts and you get almost 6500 watts, subtract for age and efficiency and that's a clean 5500W.

One of these days I have to figure out what my 6V92T burns at idle and fast idle. It just might be more cost effective to run the engine for an hour to fast-charge my house batteries than to play with all of the solar stuff, especially if I do it during the hour that I would be using microwave, deep fryer, etc and have a second generator pumping out AC.

bevans6 · June 06, 2010, 01:19:23 PM

deleted post, checking actual ampacity of wiring in the bus! No need to make assumptions when you can check facts!

I have the big DC alternator too, the whole point of this exercise is to use up some of that DC power by turning it into AC power. The problem I see with your idea of driving a surplus AC gennie head from the engine is frequency control. the output frequency will be all over the map with random RPM's driving it, as I understand it.

Actually, I really don't need to check the ampacity of the bus wiring. it is fused (breaker, actually) at 105 amps, my design load is maximum 87 amps which is 82%, add in efficiency or lack thereof and it's probably a little too close for comfort. I don't really want to run this at more than 85% steady state. I will think on this a little more. The factory motor was 1.4KW, not sure if that was it's HP rating or it's current draw.

Thanks for your comments, I appreciate them.

Brian

BG6 · June 06, 2010, 02:11:47 PM

Quote from: bevans6 on June 06, 2010, 01:19:23 PM
deleted post, checking actual ampacity of wiring in the bus! No need to make assumptions when you can check facts!

I have the big DC alternator too, the whole point of this exercise is to use up some of that DC power by turning it into AC power.

I just emailed the Optima guys to find out how fast they will take charge and discharge. If they will run the big inverter with no problems, then take a high-current charge from the alternator, that would sure simplify things for a lot of us.

bevans6 · June 06, 2010, 04:06:35 PM

why bother? the whole idea here is run the inverter while the alternator is running. The batteries are irrelevant, a pair of 8D's are ample. Mind you true AGM batteries can take a charge fast, at high current rates. I don't know how fast they can discharge without harm.

Brian

Sean · June 06, 2010, 04:18:33 PM

Brian,

I see no real problems with the plan, but I have concerns about the inverter. It says nothing about listings (other than "CE" approved), and I don't see an enclosed junction box for the hard-wire terminals. It's a poor photo, though, so maybe I am just missing it. You might be able to work around this somehow.

As for the switching under load problem, that would easily be solved by having the transfer switch you mentioned be actuated by the inverter output. This way, the solenoid will close first, energizing the inverter with essentially no load on it. Once the inverter starts supplying 120vac power, it will actuate the transfer switch, switching the load to the inverter.

One caution about transfers, though, is that the air conditioner itself might not take kindly to the transfer if it is running at the time, depending on how quickly the switch happens. Roof airs are hit and miss on this; you might be able to smooth over any transfer glitches with a larger run capacitor.

HTH,

-Sean
http://OurOdyssey.BlogSpot.com

BG6 · June 06, 2010, 04:24:52 PM

Quote from: bevans6 on June 06, 2010, 04:06:35 PM
why bother? the whole idea here is run the inverter while the alternator is running

I'm curious. You never know what my next project will be, and if there is a better way than I'm doing it now, it might be worth a redesign of what I've got.

ccbmster · June 10, 2010, 09:14:19 PM

I cant help you with the technical stuff but I can tell you that I used an Aims 5,000 watt continuous 10,000 watt peak modified sine wave inverter for three years and it performed flawlessly until I accidentally go it wet and then turned it on...ooooops. I was so happy with it I ordered another one just like it to replace it.

I got them both from The Inverter Store (which is actually an online distribution store owned by Aims). Both Aims techs and techs at The Inverter Store have been very helpful and a pleasure to deal with.

So much so that I ordered an Aims three way automatic switch from them when I ordered the last inverter. I havent hooked that up yet though and so I can not speak to how it works yet.

5B Steve · June 11, 2010, 06:05:04 AM

Brian,

I have the same problem, I want to run my roof tops without running the generator. I have one that is 13,500 the other is

15,500 BTU. Called Domenic they told me that one pulled 8.3 AMPS THE OTHER 14.8 AMPS. I placed a call to Don Rowe

inverters in Portland. They said for what I have that (24V) 2700 watt inverter would do the job. Price sounded good at

around $600.00!

Steve 5B......

happycamperbrat · June 11, 2010, 08:01:22 AM

The split air conditioners are supposed to be much more efficient then the roof tops as well, therefore easier to run on batteries and inverter alone. Just something else to consider

Chris · June 11, 2010, 02:47:44 PM

Hello.

This is my first time posting but I have been lurking on the board for some time now. We recently acquired a 1966 MC5a from my uncle fully converted and we love it.
Drove it from South Texas to Canada and back for Christmas with no issues...

Brian I appreciate this post and am actually going to try the same thing now. I am curious if a full sine wave inverter is worth the extra cost for this application. I see a modified sine wave inverter is almost half the price and dont think the AC would really perform much different with a modified wave form.

Again great post and thank you. The knowledge level on this board is very very helpful for a new member such as myself.

Chris

Sean · June 11, 2010, 05:13:00 PM

Quote from: Chris on June 11, 2010, 02:47:44 PM
... I am curious if a full sine wave inverter is worth the extra cost for this application. I see a modified sine wave inverter is almost half the price and dont think the AC would really perform much different with a modified wave form.

Welcome.

Lots of discussion on this very topic in the archives.

Without repeating it all, the short answer is that MSW waveforms and induction motors such as those found in air conditioners and refrigerators are a bad combination. You will use more energy, and that energy will be turned into heat in the motor windings. This can destroy the motor, and at a minimum it will shorten the lifespan. Also, the A/C will not cool as well. The inverter will also heat more.

If you want to run induction motors, get a true sine inverter.

-Sean
http://OurOdyssey.BlogSpot.com