Electrical help--Resources

freds · May 04, 2021, 02:31:30 PM

Quote from: OKIE9ERS on May 04, 2021, 10:51:35 AM
Now that is interesting

The other solution which I am leaning towards in reconfiguring my system is to simply do a UPS (uninterruptable power supply) type solution. Everything draws from house battery/inverter and the input side is either solar or AC power from either the generator or shore power from being plugged in.

In my case the transfer switch takes up a significant amount of space on a storage bay wall where I could mount other stuff...

richard5933 · May 04, 2021, 04:44:48 PM

If you've got a big enough charger, that could be the only thing which received power from shore power/generator.

The charger keeps the batteries topped off when the solar isn't doing enough, and everything pulls from the batteries via the inverter(s).

I like it.

lovetofix · May 04, 2021, 04:56:15 PM

Quote from: luvrbus on May 04, 2021, 10:24:18 AM
The inverters need a big enough battery bank to draw from when one is making up the difference in the power load it is not like one just makes the power

Exactly, I am also thinking a rooftop of solar and big alternator will take care of sunny days and driving time (usually night). And of course the generator covers all the other time when not plugged into 50A 240V.

freds · May 04, 2021, 08:01:57 PM

Quote from: lovetofix on May 04, 2021, 04:56:15 PM
Exactly, I am also thinking a rooftop of solar and big alternator will take care of sunny days and driving time (usually night). And of course the generator covers all the other time when not plugged into 50A 240V.

If you read my build thread I am using multiple server power supplies to simulate solar input when the sun goes down if AC power is available.

I just picked up a 1700 watt DC to DC converter (24 volt to 48 volt) so looking to make up the difference between solar and demand draw for both roof top air conditioners when I am driving.

buswarrior · May 05, 2021, 05:27:40 AM

What happened to the simple step-up transformer?

Price a suitable sized transformer before committing to all these boxes full of expensive smoke...

Happy coaching!
Buswarrior

windtrader · May 05, 2021, 10:47:35 AM

What he is doing is taking in AC and outputting DC to feed to DC battery bank. That way he can draw all power to be used via the battery and inverter.

The 24 to 48 volt DC-DC step up transformer inputs alternator and outputs and connects to the PV output side. Then that feeds the battery bank that feeds the AC.

That's my understanding based on Fred's idea to push all house usage via the battery bank and inverter.

lovetofix · May 05, 2021, 03:57:03 PM

Quote from: buswarrior on May 05, 2021, 05:27:40 AM
What happened to the simple step-up transformer?

Price a suitable sized transformer before committing to all these boxes full of expensive smoke...

Happy coaching!
Buswarrior

The step-up transformer discussion was for my system planning and is still my plan for the 240V to power my split system. Freds is doing something quite a bit different though as I believe he has a 240V inverter. Okie could use the 120 to 240 step up transformer to power his mini split if that works for him. I am thinking the step up transformer will only be useful for me while driving down the road (alternator power) or sunny days (solar power) both through a 120volt inverter I already have. When I have a 50A plug I will already have 240V and a 120 porch receptacle won't keep up with the mini split requiring the generator to run anyway which will give 240V.

Jim Blackwood · May 05, 2021, 09:59:26 PM

This discussion is helping me to refine my plans for my AC system, specifically in terms of ducting with an eye to low power operation. If there's only a 30A 110v receptacle available, (Bearing in mind that many household outlets are 15A) Much depends on the energy efficiency rating (EER) but on average there's a decent chance of powering a 1-1/2 ton unit with a good extension cord. So that has to be the default, lowest powered option and anything more is a bonus. In some cases it could be possible to do twice that, or 3 tons if the A/C was especially efficient.

Now I'm using the overhead bin mounted units for my mid level evaporators and they have a 1-1/2 ton capacity each so a compressor to drive one of those should be well able to run on said extension cord, but then it's a question of maximizing the effective use of that cooling.

I don't think it would be at all reasonable to expect it to keep up with the whole bus, but since I have bulkheads between the rear bedroom and bathroom, and again between the bathroom and the ballroom (rest of the RV) I can shut those doors and what I need then is a flapper to shut off the ductwork to the rear. And as long as I'm doing that it might make sense to do the same to the front so that I can send all the cold air either to the front, to the back, or both.

A useful refinement that I don't think I would have thought of otherwise, so thanks.

Jim

richard5933 · May 06, 2021, 03:45:29 AM

Again, with a simple hybrid inverter (one which can provide AC power boost from batteries) you should be able to provide a short-term boost to the incoming 15-amp extension cord to help with start-up loads.

Depending on how large your battery bank is, that short-term boost can be used for a much longer time period.

robertglines1 · May 06, 2021, 09:45:32 AM

Mini-split been running 120V INVERTER type mini split.. 3 in coach. will run on 30 amp 120 volt (all 3) you have no suden start up surge. The units ramp up slowly to full operation. the highest amp (max load) of a 12,000 unit is 8 amp at 120 v ac. No other hardware (transformer etc) to fail. I'm using 2ea 9,000 and 1 ea 12,000. on a 45ft coach. hottest temp I have used in was 96 F lowest was 9 F (on heat side)

Dave5Cs · May 06, 2021, 09:57:54 AM

No room for the condensers except maybe on the bumpers?

lovetofix · May 06, 2021, 10:32:18 AM

Quote from: Dave5Cs on May 06, 2021, 09:57:54 AM
No room for the condensers except maybe on the bumpers?

That is exactly my problem. Our bus will be our only home in the USA and for 2 months at a time so we need the storage bay space.
The only option I have to stay with 120V systems would be to build a custom rear cap and house the multiple condensers back there but that will take a lot of engineering and work to deal with the negative pressure behind the bus, plus there is all the dirt that gets sucked up back there.

OKIE9ERS · May 06, 2021, 02:33:58 PM

This is why, if I can figure how to do it, run 1 condenser@240 volts, and put it in the factory air condenser bay..Can run 2 or 3 inside units off of that.
Have heard many good ideas, but that has not lessened my confusion much...lol.
Thanks everyone for your input..
And...it may not be practical to go 240...
I've always considered my self mechanically inclined,, but dang!! This electrical is tough on another level..

richard5933 · May 06, 2021, 05:29:08 PM

If there is no room in the bays, what about on the roof?

There are lots of a/c systems made for roof mounting - you see them on the roof of transit buses all the time.

What if you got the fiberglass shell from one of those and used the guts out of a mini split inside it?

lovetofix · May 06, 2021, 07:55:11 PM

Quote from: richard5933 on May 06, 2021, 05:29:08 PM
If there is no room in the bays, what about on the roof?

There are lots of a/c systems made for roof mounting - you see them on the roof of transit buses all the time.

What if you got the fiberglass shell from one of those and used the guts out of a mini split inside it?

I don't have the headroom to do that, 10" roof raise. $:-\$
I think with a step up transformer I can run a 240V inverter style 3ton condenser off a 30A 120V connection or my 3500W inverter (continual rating). Even if I can't run all three evaporators that will keep me going most of the time. I believe the wiring difficulties will be easier than trying to find someone to make me a custom rear cap for my MC9.