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DawnAndChris · 05-14-2013, 11:48 AM

Hi folks.

I am upgrading my RV's electrical system. I have a new house battery bank. I am installing an Inverter and a new battery charger. My old system already has a Converter with a built-in 3 amp charger.

Where to start...? I understand that the DC runs from the battery bank to the inverter should be as short as possible. The AC runs from the inverter to the main AC breaker box can be longer. Does this sound right?

So here is where I get confused....

Do i need a plug or switch that prevents the inverter from being connected to the AC breaker box when power is provided from the generator or shore power - to make sure the inverter doesnt get back fed?

The existing DC runs meet with the Start batteries on a Coil. From there they go off to the starter and somewhere else. I am not sure where the second run is going, but my guess is that it must be going to the DC Main Fuse box. Does that sound right? The run from the house batteries to this coil and beyond are not short - way over ten feet. Does this sound like a problem? If not, should I just restore this connection to my new battery bank (keeping it the same as it was) and add in an additional DC run to the Inverter? If not.... then i guess i am thinking of moving the new house battery bank closer to the coil and closer to the DC Main Fuse box. But I only want to do this if it is benneficial and worth the effort.

Adding in the new charger.... As I understand, please correct me if I am wrong, I need an AC line to the charger and a DC line to the batteries. Again this DC line should be short. This AC line must not be connected when AC power is provided from the converter, right? I also think I am going to have to find the current charger's connection to the batteries and remove it. If this can be done as the charger and converter are part of the same unit. Does this sound right?

It would be great if someone could walk me through this a bit or give me a push in the right direction. It would be most greatly appreciated!!!

JRMEDPHYS · 05-14-2013, 12:15 PM

This is what I suggest you do.

Replace your converter/charger with one that fits into the same spot your existing one does. Bestconverters.com or something like that.

Next, install your inverter close to your battery bank. Buy a long enough heavy duty extension cord and the right adapters to match your shore cord. When you want AC from inverter, turn off your breaker for your converter/charger, plug your shore cord into your inverter, turn on the inverter and use the outlets now powered by your inverter in your coach. Make sure you don't run the A/C, microwave or fridge on AC or any other high power load if your inverter can't handle it.

If you are looking for advice on re-wiring your rig, I can't give you that through this medium with a clear conscience. It's not a job for unskilled hands.

Hope this helps.

DawnAndChris · 05-14-2013, 12:37 PM

Hi. Thanks for the advice!

The part about the inverter and shore line actually would work and would be simple and easy to do. Thank you for that!

But one question: do I just add the extra wire connection at the battery terminals and keep the existing connections in place too?

The part about the converter/charger isn't quite a fit. I will have to do something else. I already have the new charger. Do you think it is possible to diconnect the charger part and still keep the Converter part?

I have dealt with AC before; the DC part is a little new to me. I appreciate your help and you can breath with a clear concious. I am into what I am into, and I will do the best I can. Any information you share with me is just a possitive, good thing. Thanks again!

PS: I guess this is a vote to keep the long DC runs intact as they are. Still wondering if that is a good thing.

DawnAndChris · 05-14-2013, 12:41 PM

In addition... in regards to your inverter/shore line solution. We have an automatic transfer switch. If we fire up the generator and the switch kicks over to it, any chance it will back feed the inverter through the shore line? And if so, is this necessarily a bad thing?

Thanks!

JRMEDPHYS · 05-14-2013, 12:58 PM

About the battery connections to the inverter...yes. Just add some new cables from the batteries to the inverter input. Make sure the connections are nice and tight and clean and properly sized for your inverter.

About the converter/charger...No, they are a combo unit. I suggest you return the charger you have and go to the website and buy the replacement converter/charger that will fit your rig. The Progressive Dynamics converter/chargers are excellent. I don't have any idea on what sort of charger it is you have bought and the advice on how to make it work right right for your set-up may be different.

About the long DC runs...they are fine provided they are not overly resistive. That can happen if the cables are old, the connection points are dirty/corroded or if they are undersized for the application. The only way to know is to measure the resistance from end to end with a voltmeter. If too high, replace them. What's too high??? I would want it to be on the order of a few ohms and no more.

About the generator/inverter question...your system should work fine, but why tempt fate? Why would you want to run both the inverter and generator anyways? If you are turning on the generator, you don't need the inverter. So, my advice would be, if you are running off inverter, don't fire up the generator. If you are running on generator, don't plug into inverter. It is better to take a couple of minutes and do it right than rely on the "system" to work properly. It is easy to be a cautious owner and even easier to be lazy...and end up filled with regret in the end. I have had much more success with the cautious route in my experience.

DawnAndChris · 05-14-2013, 01:53 PM

Thank you very much; that was most informative!

I think i am all set on the inverter now. I just need to figure out the charger converter scenario. Maybe I will send it back. Arghh....

The reason I asked about the feedback was because the transfer switch is automatic. If i am driving down the road and the inverter is plugged in, i have to be careful and make sure we dont turn the generator on. In the past we could turn the generator on while driving. Now we will have to stop and unplug. I wouldnt have a need to run both at the same time, obviously. I was just being careful by asking what would happen if the system allowed this to happen by accident

I guess the humans must not err in this scenario as the system is quite fallible. Thank goodness I am careful too

I appreciate your help. With all things in consideration, I think this is the best solution for now. I just need to handle the charger aspect.

DawnAndChris · 05-14-2013, 02:39 PM

Good advice on the Converter/Charger!

I sent the old, "new" one back, and have now ordered a more fitting component. It is better, cheaper, and fits into my existing system.

Thanks for good advice!!!

puttin · 05-14-2013, 02:49 PM

Here's another resource, go to the site and you'll see a tab about electric stuff. It explains a good deal about re-wiring. Also "RV Electric" is good also:

Welcome to Bob & Mary's RV Site

RV Electric

DawnAndChris · 05-14-2013, 04:01 PM

Great information! Thanks puttin!

JRMEDPHYS · 05-14-2013, 04:23 PM

Quote:

Originally Posted by DawnAndChris

Thank you very much; that was most informative!

I think i am all set on the inverter now. I just need to figure out the charger converter scenario. Maybe I will send it back. Arghh....

The reason I asked about the feedback was because the transfer switch is automatic. If i am driving down the road and the inverter is plugged in, i have to be careful ...

The solution I gave you will obviously not work for you driving down the road. In this case, you would want to use the generator. Alternatively, you could install a wire from your inverter to your distribution panel but this would be a little more complicated.

Good luck.

"007" · 05-14-2013, 04:56 PM

Have you read thru the Tech Sticky above will find this info and much more.

DawnAndChris · 05-14-2013, 08:24 PM

Thanks 007!

Great information!

Having read that article, I have made some good choices: 2000 watt pure sine inverter - with a nice display for monitoring the batteries. Four 6v golf cart batteries 230Ah, wired in series and parrallel. A smart 3 stage charger. Short runs with heavy wires and 400 amp fuse.

I appreciate the advice everyone has been giving! Thanks a ton!

TQ60 · 05-15-2013, 09:02 PM

If you are OK with AC fundamentals then other than stressing the need for switching to prevent more than one source of energy to be connected at one time.

On the DC side of the house, most folks who understand AC assume that the same size wire that can run the heater can be used to power the inverter that will power the heater...wrong.

THe higher voltage of the ac circuits, 120 VAC means less current flow for the same work as that of 12 volts DC, the work performed in WATTS is voltage times amps, so the same watts at both voltages will mean 10 times the current at the 12 volt point, plus the overhead of the inverter.

The size of the wire is critical the larger the better, and the shorter the better.

THere are formulas for calculating the voltage drop, but the size depends on distance and current.

You can run a string in place of the wire, then remove the string to measure how many cable feet you have, then from that determine the exact MINIMUM size you need.

Last item is something I have rarely seen discussed here in regard to inverters, fuse or breaker.

Having a 250 amp hour deep cycle battery means you have available from 1000 to 4000 amps of short circuit current depending on wire resistance.

A circuit breaker or fuse is available that would properly protect the wiring from shorts.

THe fuse or breaker goes as close to the battery as possible.

If the wire is a short run inside the same compartment or otherwise does not have any chance of getting pinched or shorted you may be safe, but the fuse is not that expensive.

Last one we did we had some 50 amp circuit breakers harvested from the wrecking yard, we took a couple brass buss strips that are used to connect batteries together in a string and drilled holes to allow multiple breakers to be installed in parallel.

It is not the optimum, but it was free and it works.