Inverter Questions

[paul102a3]

I want to upgrade the inverter in my coach. The existing inverter is a 24 V to 120 V Vanner modified sine wave unit drawing it's DC power from the main batteries.

As a replacement, I have a Xantrex SW4048 which requires 48 volts DC. I also have a set of 8 T-105s that were used to power the inverter in it's past life.

My question is can I wire the DC side in such a way as to have the 24 V bus alternator charge the 48 V battery bank?

Thanks,

Paul

[belfert]

There are DC-DC converters that can step up, but I have to imagine that one that could handle enough amperage would be quite expensive.  I have a Samlex step down converter in my bus to run some 12 volt DC stuff on 24 volt, but Samlex only has a 7 amp unit for going up to 48 volt.

(I have a Vanner equalizer, but it was easier to find a ignition switched 24 volt source than a 12 volt one and the converter cost me $20 shipped on Ebay.)

[gumpy]

I want to upgrade the inverter in my coach. The existing inverter is a 24 V to 120 V Vanner modified sine wave unit drawing it's DC power from the main batteries.

As a replacement, I have a Xantrex SW4048 which requires 48 volts DC. I also have a set of 8 T-105s that were used to power the inverter in it's past life.

My question is can I wire the DC side in such a way as to have the 24 V bus alternator charge the 48 V battery bank?

Thanks,

Paul

The short answer is maybe.

It might be possible to wire the bus alternator to the battery with two distinct connections such that you charge half the batteries with each connection. You will probably have to put a switch in between the two halves to convert the battery from a bank of serial 48 volts to a bank of 2 - 24v parallel connected sets. Of course, this would mean you can't use the inverter when driving.

You might also look at a charge controller which is used for solar and wind charging.  It may be configurable to take 24 volts in and put out 48 volts, but I'm not real sure about this.

That inverter is designed for off grid alternate energy usage and probably won't work well for a bus. Maybe you can trade it for an SW4024 or sell it to someone looking for off grid units and just buy a more appropriate one.

[TomC]

Gumpy's advice is a good one.  Save yourself alot of hassle and switch to the 24v version.  It doesn't matter if you run 8 batteries at 48v or at 24v, it is the overall amp hours that will determine your battery running time.  Good Luck, TomC

[Sean]

I'm going to add my voice to the chorus and recommend you "trade" the 4048 for a 4024.  Even if you "lose money" on the deal, it will be cheaper than what it will take to make the 48-volt unit work in your coach.

Just as 24-volt rated equipment is more expensive than 12-volt rated equipment (compare prices, for example, of 10-watt light bulbs, or LED fixtures, or alternator regulators), usually by a factor of 50%-100%, there is also a premium for 48-volt equipment over 24-volt, often of 100%-200%.  Some items are simply not available in that rating, such as high-current automotive alternators like the 50DN on your bus.

A factory-reconditioned SW4024 can be had for $1,500.  Subtract from that whatever you can get for the 4048 (I would guess at least $900-$1,000 on, say, eBay) and you are looking at only a few hundred dollars.  You could easily spend over a thousand trying to make a 48 volt system work in a 24 volt coach.

-Sean
http://ourodyssey.blogspot.com

[paul102a3]

The SW 4048 was used in an off grid situation which we no long have so I will sell it on eBay and pick up a 24 volt version.

I didn't really think there was an easy, cheap way to do this but I have the stuff so thought it was worth asking.

Thanks for all your feedback!

[Len Silva]

You could use a 24 volt inverter only off the bus batteries to run the 4048 charger. I don't know how practical that would be and there would be more losses but it could work.

[viento1]

I think you are heading in the right direction, Sean nailed it. I like have just a 24 volt system. ONE great big battery bank and a separate 12v generator battery, just in case...

Enjoy

[paul102a3]

OK, I now have a 4024 as suggested by many on this board.

The next big question how best to wire into the bus. As stated above, the bus has an inverter already installed so the AC and DC wiring is already in place. I was planing to to utilize the existing AC wiring since it is all there and working fine.

I would like to add a separate battery bank dedicated to the inverter. I would then use the existing DC wires to add an a battery combiner so the inverter batteries would be charged from the engine alternator while under way and the house batteries would be charged from the inverters charging circuit when hooked up to shore power.

The separate battery bank will of course have it's own battery disconnect and fuse block.

Anyone see any problems with this scenario? Am I missing anything important?

Thanks

[JackConrad]

Paul,
  Looks like it should work, if I am reading it right.  Make sure the combiner has as much capacity as your alternator and is shut off when the engine is not running.  I have seen them switched by the master switch, oil pressure (so low house batteries will not draw down bus bastteries while starting) and by a dedicated switch on the dash. Another option to combine the batteries for charging from the bus alternator is an isolator. Jack

[Zeroclearance]

Jack, you mentioned about running a isolator off the alternator.   I assume that Paul has a 270amp delco 50 dn.

The question is>>  Are there 300 amp isolators made??    I have found 250 amp units but have not found one rated enough for a 270amp output?   The other solution would be to use the Xantrex Pathmaker.

[Sean]

...   I assume that Paul has a 270amp delco 50 dn.

The question is>>  Are there 300 amp isolators made??    I have found 250 amp units but have not found one rated enough for a 270amp output? 

I recommend against isolators, especially in high-power applications like this, for two reasons.  First is that the losses are unacceptably high -- you could fry an egg on the heat sink of one of these.  Second is that you need to connect the alternator sense lead to one side or the other, and the other side will probably not get the correct voltage.  I prefer, therefore, solenoids.

That being said, a 250-amp isolator is fine in this application.  270 amps is a peak value for the 50DN that is seldom achieved, and even then, chassis loads coupled with losses in the cables and the isolator itself will suffice to limit the current to a value well below 250 amps.

We have an ammeter on our intertie (solenoid type), and the most we ever see is a shade over 200 amps, and that's when the house bank is depleted and charge first starts flowing.  It always comes down below 200 amps within 15-30 seconds.

The other solution would be to use the Xantrex Pathmaker.

I also have to recommend against this product.  I have one, and used it for well over a year.  Due to the way it's designed and the way it monitors voltage, it would constantly cycle on and off, wreaking havoc with the other charge sources.  I ended up disabling the circuit board and driving the solenoid directly with an output off my Relay terminal through a delay timer.

FWIW.

-Sean
http://ourodyssey.blogspot.com

[Zeroclearance]

Sean, I was just about ready to pull the trigger on the Pathmaker!!

So it sounds like a manual switch wired to a solinoid.  I have emailed   Intellitec  and they haven't responded, business must be good for them. 

Sean if you doubled your battery bank, and were running a seperate charging system for the Coach, what do you think the highest amperage draw would be coming out of the 50DN..   I just don't want to see loads higher than the ratings..

[Zeroclearance]

Here is a good 'ol thread..

http://www.busconversions.com/bbs/index.php?topic=4150.0

[Sean]

So it sounds like a manual switch wired to a solinoid.  I have emailed   Intellitec  and they haven't responded, business must be good for them. 

I would not go strictly with a manual switch -- too easy to forget to turn it off.  I would drive the solenoid from either the old blower circuit (powered only when alternator is charger, and tied in to the "not gen" light), or, if that's not an option, the oil pressure switch.  This way the batteries are tied only when the engine is running.

I also would not buy the contactor from Intellitec -- too pricey.  All you need is a 250-amp continuous-duty solenoid, and you can get them pretty cheap from Grainger, Allied, etc.

Sean if you doubled your battery bank, and were running a seperate charging system for the Coach, what do you think the highest amperage draw would be coming out of the 50DN..   I just don't want to see loads higher than the ratings..

Again, I just don't see you being able to pull more than about 250 amps across the tie.  The chassis loads alone (charging chassis batteries, fuel solenoids, gauges, lights, etc.) should be good for nearly 20 amps, so even if the alternator was at max output (rare), you'd only have 250 amps left to cross over.

That being said, I will caution you that charging house batteries across a tie at ~200 amps puts a hell of a strain on the 50DN.  It's built for it, to be sure, but you can expect more wear and tear than someone who is not using it as hard.  Make sure it has a good oil supply, and especially that the cables are properly supported with the rests made for the purpose.  I've seen these removed by ignorant mechanics, and the resulting physical strain on the alternator can cause catastrophic failure.

We've been charging our massive house bank this way for five years, and, so far, no problems other than a burned up alternator cable (it was 00 and we replaced it with 0000), knock wood.

-Sean
http://ourodyssey.blogspot.com