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JWynn
@23.122.16.x

JWynn

Anon

[Electrical] Supply power to mobile workshop trailer

I've been reading some posts about the use of inverters in tool/workshop trailers. However, I can't find anything to help answer my question about using an inverter.

I have a 2500w inverter that I would like to mount in my newly fitted shop on wheels. I've hooked it up (on the AC side) to my distribution panel that powers all AC related circuits inside my trailer. I already have a transfer switch installed in the event I do have an available 120v hook up on site.

My dilemma/question is, If I am using a deep cycle marine battery inside my trailer to power my inverter,....is there a way to charge that battery by plugging in to my tow vehicles trailer wiring plug? If so, can it be hooked up to charge, while inverter is supplying a load to the panel, or should I turn inverter off while charging the battery? Also,...Can I eliminate the trailer battery and supply DC to the inverter through the vehicles tow wiring harness? If not,........could I run cables from battery to bumper mounted lugs, to which I could hook up inverter directly to lugs via quick type connectors? Third option, in trying to figure the best way (without site specific power supply), is.....Can inverter be hooked directly to the tow vehicles alternator? If so, what size wire (15' from battery to rear bumper) ? What size wire to use for either option?

Thanks in advance, for any help or knowledge that anyone could pass along!

JWynn

ilikeme
Premium Member
join:2002-08-27
Stafford, TX

ilikeme

Premium Member

What kind of vehicle is it? It can be possible to power off of the vehicle depending on what it is, but usually it requires a much larger alternator and second battery. The current would require its own wiring to the trailer and not run thru the existing harness. It would probably be easier and more reliable just to have a generator for the trailer if it needs that much power.
JoelC707
Premium Member
join:2002-07-09
Lanett, AL

JoelC707 to JWynn

Premium Member

to JWynn
Assuming your truck has the tyical RV 7-way plug, it does have a battery feed in it. This feed is generally intended for essentially what you are describing but it's really only used for charging the batteries in the camper while it's being moved (such as recharging the batteries after you've been out camping in it). This feed is generally fused at 30A and does not need to go higher as the stock wire is likely 12 or 10 gauge wire. It would work to recharge your trailer's battery(ies) but 30A charge isn't going to be able to sustain it during the day.

Your 2500W inverter is capable of supplying 20.83A of 120V AC power. To get that you need basically 10 times that amount (minimum) from the DC source. That means at full load, your battery will have a 210A load on it, if not higher. Obviously lower loads will draw less but a 10x increase is normal since watts are watts regardless of the voltage and you are going from 120V to 12V (a 10 fold change) and this doesn't even take into account any inefficiencies in the inverter.

To put this into perspective, the 30A available in your tow harness can only supply 360W of power or 3A at best on the 120V side of the inverter. There's not many tools you will have that can run on that little amount of power (I'll bet you have lights that pull more power than that). Simply put, I would not do this without a battery (or several) in the trailer. I would size your battery bank based on how long you need to run during the day "off the grid".

As far as using your vehicles alternator to supply or charge faster, that is possible but not practical. The issues with that are they aren't designed to supply high current like that for long periods of time. Most "high output" stock alternators I've seen top out around 120A. With the vehicle running, a good portion of that is going to the main battery to keep it topped up so you're not even going to get the full amperage there.

The other issue is idle speeds, most alternators don't put out enough amperage at idle speeds to even cover heavy local loads (idle with the air blower on high for a long period of time then tap the gas, I'll bet you notice the blower speeds up, that's because the alternator isn't keeping up with the demand at idle). You could work out some way to keep the engine throttled up but now you're talking about more noise from the revved up engine and more gas being burned.

You could get a special rewound alternator and even a secondary alternator to solve both of those previous problems (if you can find a spot to mount a second alternator on the engine) but that isn't always ideal.

My suggestion would be to size the battery bank for the run time you need or go for a generator and skip the inverter altogether. If you do want to do an inverter I'd suggest adding a charging circuit. Motor home inverters are great for this but you could piece one together if you wanted. Motor home inverters are an inverter and charger/rectifier in one. They operate on 12V DC power to supply 120V loads as needed but when connected to "shore power" (120V source) they switch to a charge mode to recharge their batteries while it can.

nunya
LXI 483
MVM
join:2000-12-23
O Fallon, MO
·Charter

2 edits

nunya to JWynn

MVM

to JWynn
This question is probably better suited for the automotive forum.

I charge my trailer mounted inverter batteries off of 1) shore power when parked at a location with power, 2) the vehicles charging system (in transit) 3) generator.

I can only speak for Ford Super Duty E/F350. I replaced the 30A fuse with a 30A circuit breaker and a 50A fuse. I have an isolator on the trailer ahead of the battery.
The aux power is normally the center pin on the 7 slot harness. It's usually an orange wire.
Most Super Duty trucks already have a H.O. alternator.

On one of my trucks, I had to tone out the AUX wire and make a connection under the dash to get it up to the power block.

The 10 Ga wire is waaaaaaaaay too flimsy to support the inverter from vehicle mounted batteries. Keep them on the trailer. You'll probably need 3/0 cable to connect to the battery bank for a 2500W system (mines 2400W pure sine wave, and 4' 3/0 can get warm). I have it fused at 200A.
Another nice thing about the batteries on the trailer is you can use 12V LED lighting inside. I also run my hydraulic pump directly from the batteries.

The key is not to overload your system or undersize your battery bank. You don't want it constantly depending on your vehicle charging system. If you have a decent inverter, you should be able to program the inverter cutoff voltage. Keep it as high as you can. Consistently draining the batteries below suggested discharge voltage is bad.
I've seen some that will let you set it down to 10V. That's a battery murderer. I'm a nervous mervous, so I keep it at 11.5V and really don't like that.

Edit: I should add that I have "idler boxes" on my trucks. They use the PTO setup to idle the engine for charging. I put a POT on there to adjust from 900 RPM to 2400 RPM.
I can get you the directions for Ford Super Duty. I don't know if GM has this option.
iknow_t
join:2012-05-03

iknow_t to JWynn

Member

to JWynn
you could change out your alternator for a 240 amp Leece Neville and run 3/0 welding cable with quick connect welding connectors on it to the trailer, but you really would be better off with a generator, it'll be much better on gas.. smaller engine vs v8..

thick
@50.138.50.x

thick to JWynn

Anon

to JWynn
as others have mentioned, the current the inverter draws from the battery is large, requiring thick cables.

use the wrong but right general rule of thumb: 10:1 .
you are inverting 12 volts to ~120 volts. that's a 10:1 conversion.
so the amps is opposite, 1:10 conversion. your 2500 watt inverter will be supplying ~ 20 amps, at full load,
so the inverter will be pulling 10x that in amperes from the battery.
about 200 amps.

there are two ways to do what you are thinking of.
1
put another alternator and another battery under the hoodm (or just a 2nd battery with an isolator diode block),
then use thick wires and thick quick-connectors for the wires back to the inverter.
the thickness of the wire will be bout the same thickness as the wire from the battery to the starter.

2
put the inverter near the motor, so the thick wires are short, and then just run the thiner 120 volts ac back to the trailer.

yes, you can charge a trailer battery from the towing wires, but only slowly, say 20 amps, instead to the 100 amps an alternator could deliver.

yes, all these calculations are based on your pulling full 2500 / 20 amp load from the inverter. if you are really only using 250 watts / 2 amps from the inverter, everything's easier.

PSWired
join:2006-03-26
Annapolis, MD

PSWired to JWynn

Member

to JWynn
One thing that hasn't been mentioned is the type of usage you're planning for. Unless you have your tools running constantly, I'd expect a low duty cycle for the inverter. So you're not drawing 200A from the vehicle constantly, only intermittently. It could be that you'll be fine charging from the 30A trailer connector if your usage is light.

chip89
Premium Member
join:2012-07-05
Columbia Station, OH

chip89 to JWynn

Premium Member

to JWynn
This Honda Generator is the best beat instead of a battery set up. »m.powerequipment.honda.c ··· /eu2000i
iknow_t
join:2012-05-03

iknow_t to JWynn

Member

to JWynn
another thing to consider is that deep cycle batteries are not designed to be fast charged.. I know someone that damaged a brand new deep cycle hi-low battery(very large) by using it in his car with a 100 amp alternator.. more like 20 amp charge is better.

nunya
LXI 483
MVM
join:2000-12-23
O Fallon, MO

nunya

MVM

That's why Optima are worth the extra $$$.

JWynn
@23.122.16.x

JWynn to nunya

Anon

to nunya
Wow! Thank you all for the posts and suggestions. Sorry I have not been able to see your replies until now. This past week I was actually in the situation which I am trying to prepare for. In an isolated part of the county with little or no comms and no power. I do have a 3200w generator, but I want to be able to use the inverter option as well. The noise level is my concern during 8 hours of constant running the generator.

Nunya, I would appreciate the directions for Ford Super Duty. The truck I use in combination with my trailer is a 2005 F250 (gas burner) Super Duty. 5.4L with 7pin round connector and 4pin flat. However, I have just about any adapter configuration to fit any trailer plug.

I have to say, some of the great information in everyone's post gets "above my head" on the technical jargon. I know a great deal on wiring when its AC voltage. DC, on the other hand, can be difficult for me at times.

The usage demand would be intermittent and not constant. The charging I want to do would be only during rest periods (no usage demand/load from the inverter). Basically, max load would be 3hp compressor, circular saw, radio, and miter saw. Intermittently of course. Looking for a trailer mounted system solution with a quick connect/disconnect solution to tow vehicle (if needed for charging).

chip89
Premium Member
join:2012-07-05
Columbia Station, OH

chip89

Premium Member

The One I fought of is only 59DB anyway you whould have to keep you Truck running anyway.
LittleBill
join:2013-05-24

LittleBill to JWynn

Member

to JWynn
air compressor is going to kick your ass, you will need to leave the truck running, a single battery isn't going to cut it either

nunya
LXI 483
MVM
join:2000-12-23
O Fallon, MO
·Charter

nunya to JWynn

MVM

to JWynn
You can forget about the 3HP compressor. That will dim the lights on a 100A service, let alone a 2.5 kW inverter (it will overload the inverter straight away).
I run my P.O.S. Porter-Cable pancake compressor off of my inverters all the time, but that's definitely less than 1 HP.

John Galt6
Forward, March
Premium Member
join:2004-09-30
Happy Camp

John Galt6 to JWynn

Premium Member

to JWynn
When you need -really- good batteries:

»www.odysseybattery.com/
iknow_t
join:2012-05-03

iknow_t to JWynn

Member

to JWynn
that 3 HP compressor is going to make a heck of a lot more noise than a generator if it's the direct drive type.. and I know even a 4000W generator isn't enough to start a 2 HP compressor.. so, you WILL have to seriously contemplate the truly workable options, and forget what you would like.. either a setup that will run everything you need, and be quiet, or a setup that will run everything you need, and be a bit noisy, or a setup that will be quiet, but only run minimal needs for a short time.. think about what you really NEED.... and also, the price to run it, and how long it will operate what you need.. a separate generator maybe 8,000 watt may be the cheapest way to run what you want, also, a belt driven compressor, and a motor home type muffler for the generator, those are very quiet.. getting 8,000 watts from a battery bank for 8 hours is going to be very expensive, just for the batteries.. also, the truck engine will consume a lot of gas running the huge alternator you'll have to retrofit in it.. an 8 cylinder engine is very large to run such a comparative small load..
JoelC707
Premium Member
join:2002-07-09
Lanett, AL

JoelC707 to JWynn

Premium Member

to JWynn
I have a 3500W generator and it wont even begin to start a 5HP 240V belt drive compressor. I'm sure if I gave it a quick spin to help it along it'd run it just fine but it's the starting (locked rotor, LRA) power needed that is too great for the generator.

You can also forget about running it from the 2500W inverter. 1HP is roughly equal to 750W so 3HP is roughly 2250W. That's running wattage, expect at least double if not triple that for starting. The inverter wont be able to provide that much power and even if it could, you're pretty much loading it to 100% so you won't be able to run anything else on it and devices aren't really designed to be run at full capacity regularly.

The saws should be no problem to run from the inverter, they run from mine with no issues. I have also run a 1.5 HP or so direct drive compressor off my 2500W inverter and it sometimes had issues starting it with just a single group 27 marine battery connected. I had to use jumper cables to the truck battery to provide a boost.

JWynn
@23.122.16.x

1 recommendation

JWynn to iknow_t

Anon

to iknow_t
Yes, iknow_t, even though I admittedly don't know much about DC wiring, I have nearly decided from the information everyone has given me, that my WANTS aren't going to be a feasible option for me. So, yes, the generator looks like the viable option. However, I do think I am still going to wire in the inverter as well for the corded power tools, chargers, and such. I'll run the generator only "as needed" for compressor and possibly battery charging.

I normally don't seem to get any REAL help when I have asked questions on other sites. I am definitely impressed and appreciative of the responses everyone has given!! Ya'll have educated me a little, and given me some good options to consider. THANKS!

shdesigns
Powered By Infinite Improbabilty Drive
Premium Member
join:2000-12-01
Stone Mountain, GA

shdesigns

Premium Member

Another option is a gas powered compressor.