Electrical for Dummies

[emilyweav]

Would anyone be willing to walk me through the basics of the Airstream electrical system? I thought I had a handle on the basics but then I see comments about inverters/converters that I don't understand when I thought I had the information I needed. I understand the two powered system and that you need a converter for powering lights and things on shore and charging batteries and an inverter for powering the outlets and extras when on battery. I also saw someone said if you get a charging inverter you don't need a converter but I don't know how that would work. Basically I'm starting from scratch and just need to know what to buy and hopefully as inexpensive as possible (while still having good quality). Please help! Thanks in advance!

[uncle_bob]

Hi

Actually you are a lot further along than you think you are.

An inverter / charger ( or hybrid inverter or inverter / converter ) is just a new box to toss into the mix. They found that putting the inverter in the same box as the converter saved a bit of money. That makes them a popular item if you are upgrading.

So: Draw a little line around your mental image of a converter and a separate inverter. You now have something like the inverter / charger.

System wise, it's a bit of an odd beast. You can have power flowing from the box to the battery ( when it's a charger ). You can have power going the other direction (when it's an inverter ). The same cable handles both currents. That saves you a bit on copper. It makes you wonder which end gets the fuse...

Some inverters have external transfer switches. ( what switches the output from shore power to inverter power). All the inverter / chargers that I know of have built in transfer switches. That's not to say they all do, just that the popular ones do.

About the only down side to an inverter / charger is that you can't pick quite as many options. If I go converter / charger shopping, I can get one in every charging current level from 10 amps up past 120A in 5 or 10 amp steps. I can then go buy a separate inverter at maybe 350W to go with my 120A charger. (Why you would do that combo ... no idea at all .... seems crazy). The cost of each is proportional to how big it is.

With the combo inverter / charger, I get a big charger with a big inverter and a small charger with a small inverter. The transfer switch likely also scales as well. Price isn't to bad when compared to all the parts I do get. If I compare to a really weird setup like the 350W plus 120A, I'd be paying a bit more money.

With any big inverter, cables (and batteries) can get a bit out of hand. If your inverter ( any inverter) is putting out 3KW to run your trailer, it's pulling more than 3KW off the battery to do it. You will run more than 250A in this case and it could easily be up above 300A. That gets you into cable with a bunch of zeros in the AWG (like 4/0 or more likely larger...). You will need > 400AH of battery to keep the discharge currents reasonable.

With your 4/0 cable and 250A, you will get a voltage drop. The drop in both the + and the - leads counts. If it's 30 feet from battery to inverter, you have drop in 60 feet of wire. Loss will be about 3/4 V in this case.

So, that's sort of a roundabout walk through electrical in your RV. It most certainly does not cover everything and anything. It would take a couple of pretty big books to do that. I suspect it does fill in the gap that was giving you the trouble.

======

A bit further afield ( = not as important). A "3,000W" inverter may be a lot of different things. It may be a device that puts out 3000 VA ( not the same as watts) and only will do 2,400 W. It may also be a device that can put out 6,000 W for 30 seconds.

In the case of 6,000W for 30 seconds, what comes out the AC side must come in the DC side. You now have >500A rather than 250 to 300A. Your drop is about 1.5V and not 3/4V. You need heavier wire .....

Bottom line: you very much need to read the fine print. Some manufacturers are more detailed in their specs than others. You also need to understand what your loads are. The 3KW in all the above is a pretty nutty load for an inverter in a trailer. It likely means you are running the air conditioning on your inverter. That's a mighty big bunch of batteries you have there ....

Bob

[vintagemotor]

Originally Posted by uncle_bob

Hi

Actually you are a lot further along than you think you are.

An inverter / charger ( or hybrid inverter or inverter / converter ) is just a new box to toss into the mix. They found that putting the inverter in the same box as the converter saved a bit of money. That makes them a popular item if you are upgrading.

So: Draw a little line around your mental image of a converter and a separate inverter. You now have something like the inverter / charger.

System wise, it's a bit of an odd beast. You can have power flowing from the box to the battery ( when it's a charger ). You can have power going the other direction (when it's an inverter ). The same cable handles both currents. That saves you a bit on copper. It makes you wonder which end gets the fuse...

Some inverters have external transfer switches. ( what switches the output from shore power to inverter power). All the inverter / chargers that I know of have built in transfer switches. That's not to say they all do, just that the popular ones do.

About the only down side to an inverter / charger is that you can't pick quite as many options. If I go converter / charger shopping, I can get one in every charging current level from 10 amps up past 120A in 5 or 10 amp steps. I can then go buy a separate inverter at maybe 350W to go with my 120A charger. (Why you would do that combo ... no idea at all .... seems crazy). The cost of each is proportional to how big it is.

With the combo inverter / charger, I get a big charger with a big inverter and a small charger with a small inverter. The transfer switch likely also scales as well. Price isn't to bad when compared to all the parts I do get. If I compare to a really weird setup like the 350W plus 120A, I'd be paying a bit more money.

With any big inverter, cables (and batteries) can get a bit out of hand. If your inverter ( any inverter) is putting out 3KW to run your trailer, it's pulling more than 3KW off the battery to do it. You will run more than 250A in this case and it could easily be up above 300A. That gets you into cable with a bunch of zeros in the AWG (like 4/0 or more likely larger...). You will need > 400AH of battery to keep the discharge currents reasonable.

With your 4/0 cable and 250A, you will get a voltage drop. The drop in both the + and the - leads counts. If it's 30 feet from battery to inverter, you have drop in 60 feet of wire. Loss will be about 3/4 V in this case.

So, that's sort of a roundabout walk through electrical in your RV. It most certainly does not cover everything and anything. It would take a couple of pretty big books to do that. I suspect it does fill in the gap that was giving you the trouble.

======

A bit further afield ( = not as important). A "3,000W" inverter may be a lot of different things. It may be a device that puts out 3000 VA ( not the same as watts) and only will do 2,400 W. It may also be a device that can put out 6,000 W for 30 seconds.

In the case of 6,000W for 30 seconds, what comes out the AC side must come in the DC side. You now have >500A rather than 250 to 300A. Your drop is about 1.5V and not 3/4V. You need heavier wire .....

Bottom line: you very much need to read the fine print. Some manufacturers are more detailed in their specs than others. You also need to understand what your loads are. The 3KW in all the above is a pretty nutty load for an inverter in a trailer. It likely means you are running the air conditioning on your inverter. That's a mighty big bunch of batteries you have there ....

Bob

This is the best and most correct description I have ever heard!

[Bill M.]

Been traveling for about 5 months a year fo the last 12 years and do not have an inverter nor any plans to add one. I put in a Boondocker converter from Best converter. I did have a $25 plug in inverter fron Autozone to run my CPAP but now I have a 12 to 24 volt adaptor that does that better. I do sometimes carry a generator for recharging and if we feel the need for 110 or to run the AC. Inverters use battery power at a very high rate. After reading Uncle Bobs good explanation I would install the converter and the inverter separately if I wanted both.

[TG Twinkie]

I agree with Bill M.
You can get a 3 stage converter rated at 45 amps for around $150.
Shop for it on eBay.
Progressive Dynamics is a good unit.

Sent from my VS500 using Airstream Forums mobile app

[emilyweav]

Thank you so much! That clears up so much of my confusion. I have a 31 foot Sovereign and I plan to only use the shore power for the ac (original armstrong if it works *Crosses fingers*) and smaller things like Television and maybe occasionally the microwave. What would you recommend as far as converter and inverter? There are so many different options I don't even know where to start

[OTRA15]

This Battery School site is good background reading:

http://www.batteriesnorthwest.com/batteryschool.cfm

. . . although it may not cover all the bases you asked about.

Good luck,

Peter

PS -- Some very basic definitions -- To Keep It Simple, Stu:

Battery voltage is 12 volts direct current
Shore Power is 120 volts alternating current

Inverter -- changes 12 volt direct current into 120 volt alternating current
Converter -- changes 120 volt alternating current into 12 volt direct current

uncle bob's Post #2 goes into more detail on some of the permutations of these two basic "boxes."

[uncle_bob]

Hi

First thing to look at is what the converter that is in the trailer now is rated for. By far the easiest swap is going to another one with the same ratings. That way the wiring and fuses should all work ok. Even with a direct swap it's still worth double checking.

Very arguably, the best thing on the market is the Victron stuff. It's not cheap, but they are well made and they have detailed specs on them. The unit you get will meed the specs on the sheet. Since they are designed for a variety of applications, they will not drop straight into a location currently occupied by an RV specific converter. There will be a bit of this and that needed for the mounting.

Geting an inverter depends a lot on what you will be running. The microwave likely pulls 1300W (maybe more / maybe less) That gets you into a > 1KW inverter. Stuff like a modern flat panel TV should be down in the < 200W range. Chargers for phones and computers should be < 100W each. If something like a coffee machine is in the mix, they pull a lot of power ( = more like a microwave ). How much each item *actually* pulls depends very much on what you have. All of the above are rough guesses.

Any conversation about *using* and inverter should also get into batteries. As an example,a 1300W microwave will pull > 100A off of the batteries when it is running. If you have a pair of group 24's, you have about 80 usable AH when they are brand new / fully charged. Fifteen minutes ( at full power ....yikes ...charcoal for dinner) will probably use about 1/2 of your battery. What? Well, high discharge rates pull a lead acid down much quicker than slow discharge. The 80AH is based on a slow discharge.

Who you get some of this stuff *from* matters at least as much as what you buy. Joe Random seller on the internet may not be able to give much help to you if there is a bump in the road. To me, it's *much* better to buy from somebody who answers the phone when you need help. I can personally attest that Randy at Best Converters answers the phone at all sorts of weird hours. I believe the same is true of the guys at AM Solar. Based on my calls to him, Peter Kennedy at PKYS also is quite good for support.

Keep in mind that even bought brand new, there is no guarantee that the gizmo you get will be perfect. Shipping damage does occur. Sometimes it's very hard to detect. Other times it's blindingly obvious. Some new gear lasts a week or two and then goes nuts. Other gear comes in with instructions that are .... difficult ... There are lots of reasons a voice on the other end of the phone is a really good thing.

Lots of twists and turns ....

Bob

[Bill M.]

I like the Boondocker converter I put in and would recommend it. I went with the 65 amp. Would be good with a pair of AGM batteries. You only need a inverter if you want to run 110 appliances and things while not hooked to shore power. When plugged in to shore power it is just like at home. So the inverter only if you want to run a substantial appliance while not hooked to shore power or a generator. A hair dryer or a coffee pot will drain your batteries in an hour or so when run on an inverter. ( It is a temptation for the coffee maker though. ) But I know I do not have enough battery power to support it. Instant coffee from water heated on the stove on dry camping mornings unless we have the generator running for a recharge.

Unless you are going to add solar a converter is the piece you really need. I used the old 12 volt fuse panel but a new fuse panel would be a good upgrade on a rebuild if you have access to the old one.

I know nothing about solar except that it is technical and expensive. I do know how to start a generator.

[Lumatic]

Someone mentioned above Best Converter. Randy is very knowledgeable and will steer you right.

Does your Sovereign have the original Univolt converter? It may work but is not very efficient and can damage your battery. If you replace it you will also need a new fuse panel or you can scavenge the one from the Univolt.

I replaced my Univolt with a 45 amp Progressive Dynamics Intellipower which works very well. The size of the converter depends on what kind of electronic bells and whistles you have.

If you don't have it get a service manual (not an owners manual). Occasionally you can find a used one but new photocopies are available from Secretarial Services in Elkhart Indiana. The first year service manuals were available was for 1972.

[uncle_bob]

Originally Posted by Bill M.

I like the Boondocker converter I put in and would recommend it. I went with the 65 amp. Would be good with a pair of AGM batteries. You only need a inverter if you want to run 110 appliances and things while not hooked to shore power. When plugged in to shore power it is just like at home. So the inverter only if you want to run a substantial appliance while not hooked to shore power or a generator. A hair dryer or a coffee pot will drain your batteries in an hour or so when run on an inverter. ( It is a temptation for the coffee maker though. ) But I know I do not have enough battery power to support it. Instant coffee from water heated on the stove on dry camping mornings unless we have the generator running for a recharge.

Unless you are going to add solar a converter is the piece you really need. I used the old 12 volt fuse panel but a new fuse panel would be a good upgrade on a rebuild if you have access to the old one.

I know nothing about solar except that it is technical and expensive. I do know how to start a generator.

Hi

My Boondocker blew up after two weeks and nuked about $400 in LED lights. It may have been a random occurrence. I still would have a hard time recommending them or the same looking units with a different label on them. Not a knock on Randy, he's a fine guy and does not build them himself. Simply an observation that none of this gear is perfect.

Bob

[LY007]

Good discussion!

While we have always had combo inverter/chargers in our RVs, the only time we have ever used the inverter was to run the coffee maker in the morning when boondocking around other people, not wanting to be a bad neighbor by running the generator at 6am. And more often than not we just used a percolator on the stove. So, frankly, the inverter part of the box was rarely ever used, and we have yet to use it in our current AS.

[A W Warn]

Originally Posted by emilyweav

Thank you so much! That clears up so much of my confusion. I have a 31 foot Sovereign and I plan to only use the shore power for the ac (original armstrong if it works *Crosses fingers*) and smaller things like Television and maybe occasionally the microwave. What would you recommend as far as converter and inverter? There are so many different options I don't even know where to start

I second the recommendation to contact Randy at Best Converter.
http://www.bestconverter.com/
He and his staff are very helpful.
When I called them, they asked me all the right questions and helped me select the converter that worked best for my trailer and how I use it.

[A W Warn]

Originally Posted by uncle_bob

Hi

My Boondocker blew up after two weeks and nuked about $400 in LED lights. It may have been a random occurrence. I still would have a hard time recommending them or the same looking units with a different label on them. Not a knock on Randy, he's a fine guy and does not build them himself. Simply an observation that none of this gear is perfect.

Bob

I have Boondocker converters in both of my trailers. So far I have been very satisfied. Just yesterday I was checking the battery. The present wet cell battery has lasted longer than any battery in my Safari since I owned it. ~3 years and still going.

Yours is the first bad Boondocker experience I've heard of. Did you get another Boondocker under warranty or go with a different brand?

[uncle_bob]

Originally Posted by A W Warn

I have Boondocker converters in both of my trailers. So far I have been very satisfied. Just yesterday I was checking the battery. The present wet cell battery has lasted longer than any battery in my Safari since I owned it. ~3 years and still going.

Yours is the first bad Boondocker experience I've heard of. Did you get another Boondocker under warranty or go with a different brand?

Hi

As instructed, I called the people at the factory and dealt with them for a replacement. I have not yet seen that come in. I have no desire to put the replacement in the trailer. LED lighting costs to much to replace. Indeed, I could have lost something much more expensive than the lights. I've gone with a Victron Multi from PKYS.

Do I believe that the converters are junk? Certainly not. Something about the one I had wasn't quite right *or* there is something weird about my trailer. Saving a couple hundred and risking another many hundred problem .... not a good idea to me.

Bob