??? Wiring an inverter to use 12v to power my cabin

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??? Wiring an inverter to use 12v to power my cabin

Postby coachgeo » Thu Jul 24, 2008 8:21 pm

ok, my cabin is wired same as an RV but WITHOUT a 12v supply. It only has the 3 pin big 220ish looking typical RV powper cord and plug. The cabin is designed to be installed in RV parks as a rental unit that is why it is wired like an RV's 110v system. Its not light duty though. The cord carries enough juice for 2 burner electric stove*, 15gal Hot water heater*, Apartment sized fridge, lighting, small *AirCon/heater etc.. Its wiring meets US standards for homes w/fuse box etc.

*these items being removed and replaced with LP units or some other non power draw from the battery bank.

I bought a 3000watt/6000surge 12v inverter/charger to run this off of a 12v battery bank. The cabin is set to be totaly off grid. I have a generator for charging the battaries.

Unfortunately the inverter is not a hardwire setup. It has two 1500W plug recepticals. Two wall plugs for each 1500W receptical are mounted on the back of it.

Sooooo... how is the best way to get the full 3000 Watt into the RV Plug to power the whole rig off one 3000w at 120v feed?

Can I make a pig tail that consist of:

. Use a thick power cord for each of one plug from each side of the inverter's 1500W recepticals and put them into into a small power box. Each power cord handeling potentially 1500w

...or would it be best to use all the plugs splitting the potential juice per power cord into 4 loads of 750w instead of two loads of 1500w

. Place in this box a female RV receptical.

...Wire all set of power wires coming in off the inverter's 1500w sides into the one RV female receptical in the box

... Hot to hot, Ground to ground etc. for a total of 3000W.

. RV plug from cabin would then plug into this giving me 3000w total capabilty within the cabin all thru the one circuit as it is designed.

certainly hope I dont have to go up one more inverter size that is made to hardwire. Its more inverter than what I need and its 200 more dollars I dont have.

Just hoping to avoid a rewire of the cabin into more than one set of wiing and breakers, rather it be two of 1500w each or 4 at 750w. Much rather stick with the one power in and breaker system it is made for.
Last edited by coachgeo on Thu Jul 24, 2008 9:47 pm, edited 1 time in total.
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Postby coachgeo » Thu Jul 24, 2008 8:51 pm

found more data on the preinstalled electrical

Electrical Package

50AMP box with breakers includes 1 interior & 1 Exterior GFI receptacle, outdoor coach light, 2 light fixtures & all wiring, wall switches & receptacles to NEC code.

Kitchennette Package

. 2 burner electric cook top stove,
. 4.3 cu. ft. under counter refrigerator
. 10-gallon Electric Hot Water heater
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Postby SunWizard » Thu Jul 24, 2008 10:35 pm

The biggest trouble is that the water heater and stove are probably 220v. That inverter will only do 110v. The max of the outlet is probably 15 amps, so the most you will get even if you hooked a plug into both outlets is 15a, unless its wired internally so that each plug is 15a. Only the inverter instructions can tell you that. But there is no way it does 220. You need something like the trace/xantrex inverters which have a stacking option where you add a cable connecting 2 inverters and then get 220v.
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Postby coachgeo » Thu Jul 24, 2008 10:36 pm

SunWizard wrote:The biggest trouble is that the water heater and stove are probably 220v. .
It is wired for RV spot hook up. Nothing is 220v

Besides as mentioned the 10gal hot water heater and the 2 burner elec. stove are being replaced with LP items.
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Postby coachgeo » Thu Jul 24, 2008 10:44 pm

SunWizard wrote:... The max of the outlet is probably 15 amps, so the most you will get even if you hooked a plug into both outlets is 15a, unless its wired internally so that each plug is 15a. Only the inverter instructions can tell you that. ....
cant find the amps in the instructions only that each bank of plugs on the back (2 of them) are 1500w each
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Postby coachgeo » Thu Jul 24, 2008 10:51 pm

correction EACH of the 4 plugs on the back are listed at 1500w max. Makes since because the surge size is 6000w.

It's 3000w continuous.
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Postby Burbarian » Fri Jul 25, 2008 12:56 am

Converted a big diesel school bus into an RV 6 years ago. Used a half dozen small 200W and 400W inverters all around, and a pair of 1200W units. You only activate the specific inverter wired to supply a particular load. No single large 110VAC loads in the bus exceeding 1kw. Rarely more than 1 or 2 of the small inverters running at any given time. Helps reduce costs and parasitic load, and provides a large measure of redundancy. Circuit breakers all around. Sold it 2 years ago to a neighbor who then went and bolted 4 banks of Harbor Freight 3'x3' solar panels on the roof, mounted on folding frames.
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Postby SunWizard » Fri Jul 25, 2008 6:50 am

You would have to ask the inverter maker if its OK to hook hot to hot with plugs in both of the receptacles. It should be OK since the waveform phase should match.

You would also need to check the breaker box in the unit and make sure there is only a single 110v coming in and all the breakers are on the same hot wire.
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Postby coachgeo » Fri Jul 25, 2008 7:08 am

SunWizard wrote:....You would also need to check the breaker box in the unit and make sure there is only a single 110v coming in and all the breakers are on the same hot wire.
Not following you, or your not following me??

This is like an RV.... there is only one powercord, only one path of power into the cabin, only one breaker box.... unless they split it at the box into two or more different paths???????
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Postby coachgeo » Fri Jul 25, 2008 7:13 am

Burbarian wrote:Converted a big diesel school bus into an RV 6 years ago. Used a half dozen small 200W and 400W inverters all around, and a pair of 1200W units. ....
I would have to rewire the whole cabin to do this. My first assumption was I could use the OEM wiring on a 12v load and do like you suggest with several inverters. Then discovered the OEM 110v power lines cant handle that task.

Now it was either rewire the whole thing or just get on large invertor.

Rewire; not an easy task since it is a log cabin. There is no space in the walls to snake new wires etc. would have to run wires around door jams etc. Would look real hoaky. Its not fake log...Walls are solid. Only real choice is buy larger inverter. Now Im here.
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Postby Burbarian » Fri Jul 25, 2008 1:27 pm

SunWizard wrote:You would have to ask the inverter maker if its OK to hook hot to hot with plugs in both of the receptacles. It should be OK since the waveform phase should match.


Absolutely essential to check with manufacturer. Or failing that, a phase discriminator or an old school differential oscilloscope to check for phase difference.

Unfortunately, phase matching is not the only issue. Depends on how the receptacles are wired internally. If they are all wired in parallel to a single bus bar or had mosfet switching in parallel from a single synthetic sine wave clock generator, then yes.

However, some designs use bipolar oscillation of single elements and then just recombine the half waves separately to different outputs. Something like the reverse of a full bridge switched rectifier. This is more common in designs that still use iron core transformers in a hybrid setup, and will have either 2 outputs at 180 degrees out of phase, or 4 outputs at 90 degrees out of phase. These cannot be ganged together in parallel.

Also, if these use lead-edge triggering and the manufacturer just ganged 4x 1500W load capacity semiconductor switching elements, then although each bank can independently sink 1500W, if they are tied in parallel the entire bank will still only be able to sink 1500W. Since they are switched in parallel, the waveform and phase will be a perfect match, and they can be wired in parallel (hot to hot), but they cannot be loaded in parallel. This is because the first (fastest) of the 4 that switches, will immediately block the 3 others from switching, similar to paralleling 2 SCRs. You don't double the capacity. This is often exploited in synchronous redundant circuits, where if one switch fails, the second (slightly slower) circuit automatically takes over. But in a ganged inverter it will not multiply the single peak load. You can have a total maximum parallel load of 6000W consisting of 4x 1500W individual loads each sinking from one of the elements. (By element I mean 1 of a modular set of bipolar semiconductor switching modules. ) This is often done in order to save costs as in most cases 4x 1500W capacity elements are cheaper than a single 6000W. This allows the manufacturer to CLAIM 6000W, while in fact not being able to supply 6000W to a single unique load.
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Postby coachgeo » Fri Jul 25, 2008 1:33 pm

After reading what Burban says I dont know what to think. here is the recent events


after talking to two people in the know, well one of them addmitingly 1/2 in the know it looks like it won't be too difficult unless Burban is right.

The 1/2 fellow said... "it may well be that the full power is split into the plugs at the back of the unit right by the plugs". So .. I took the back off of the inverter and he is correct. It's all right there by the plugs. Only Two lines +- feed the four plugs. They are obvious +Red -black, so I would think one could jump off these two lines and these two would give me full coppacity.

So it looks like I can just wire into the inside in the back and pull full wattage from there and into a female trailer plug receptical.

Looks like If I pull the power source AFTER the first 15A breaker I can use the on board breaker too.

The second Gent.... is in the know. An electrician. He felt twist locks on would be fine and I do not have to soder. Now that I think about it. Homes are wired with twist locks

Is "twist lock" the right term?

I'll try to draw a diagram so you folk can see better what Im thinking and shoot it down or say it looks plausable.
Last edited by coachgeo on Fri Jul 25, 2008 2:10 pm, edited 1 time in total.
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Postby coachgeo » Fri Jul 25, 2008 1:43 pm

Here is the plug wires.... hmm... crap... I cant post pics in here.


PLUG--------------- PLUG
+ +
+ +
+
+
PLUG

CRAP.. cant post ASCII either
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Postby Burbarian » Fri Jul 25, 2008 1:51 pm

coachgeo wrote:So .. I took the back off of the inverter and he is correct. Its all right there by the plugs. Only Two lines +- feed the four plugs. They are obvious +Red -black, so if I would think one could jump off these two lines and these two would give me full copacity. so it looks like I can just wire into the inside in the back and pull full wattage from there and into a female trailer receptical.


Then you're good to go. That's the first design I mentioned, where the 4 receptacles are wired in parallel to a single bus bar. That will allow you to tie the receptacles in parallel, or even better, to draw directly from the two bus bar conductors. No worries about phase and individual loading. Note that there are no unique (+) and (-) lines in AC circuits, as they alternate.

Looks like If I pull the power source AFTER the first 15A breaker I can use the on board breaker too.

The second Gent.... is in the know. An electrician. He felt twist locks on would be fine and I do not have to soder. Now that I think about it. Homes are wired with twist locks

Is "twist lock" the right term?

I'll try to draw a diagram so you folk can see better what Im thinking and shoot it down or say it looks plausable.


Keyed twist lock plugs and receptacles are preferable. You can't plug it in wrong, and a short turn locks them together so they don't wiggle free. Good strong positive contact on the conductor surfaces prevents intermittent or loose bridging, which causes accelerated oxidation, resistive heating, and a potential fire hazard.

The vast majority of high current residential and commercial wiring uses simple chevron shaped anvils that squeeze the electrical conductor under pressure from a screw. No need for solder in most cases unless the conductors and connectors used are near their capacity limits or if you expect hostile operating conditions like high humidity and vibration.
Last edited by Burbarian on Fri Jul 25, 2008 1:53 pm, edited 1 time in total.
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Postby coachgeo » Fri Jul 25, 2008 1:53 pm

[PLUG]-negative jump-[PLUG] --- Also Negative main line input from inverter

+Positive jump from both to plug below them
-Negative jump from both to plugs below them

[PLUG] {No jumps across} [PlUG]

+Postive jump from both plugs to 15A circuit breakers below

[15A] w/ + jump across [15A]

+ wire feeds left side as the sole power input.
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