50DN to run Roof Air

[travlinman]

I'm Considering this upgrade:

Running down the road I would like to run my roof air off my newly rebuilt 50DN alternator. Here are the specifics of my system.

1962 4106
8v71 NA
50DN Alternator
2 8D 800cca start batteries
Magnum Energy MS2812 Inverter  http://www.magnumenergy.com/Products/MSseries.htm
Dometic Roof Air 459530 http://dometic.com/10436664-32fa-4b25-8067-c8a5538a1dcc.fodoc

My system is already set up to run off my house batteries via a 12 volt Diesel Battery Charger - http://www.amplepower.com/products/bdbc_enermatic/index.html

Here is my main question, can I run the roof air off the start batteries with the engine alternator suppling the charge?? If so, how??

This would give me two methods to keep the bus cool running down the road and find a use for that big alternator.

Thanks for your thoughts and advice,

TM

[JohnEd]

I don't think you need to involve your start bats.  The house bats are being charged while the engine is running so you have a amperage source available at them that exceeds the bat current possible.  You only need 12 amps at 120VAC to run the ac unit and something less than 20 amps to start-up.  While the ac load will never max out the inverter, what is the max current the inverter can draw at 12 volts?

[muddog16]

The best way to answer this: JohnEd is correct and here is a link to Sean's site....schematics and explanations, it doesn't get any better than Sean's explanations!  Good luck!

http://ourodyssey.us/bus-conversion.html

[Boomer]

Call Dick Wright at Wrico.  He can provide a relay and diagram to divert a portion of the alternators output to your house bats.  Just did this on my brothers 4106.

[bevans6]

I do this, albeit on a MCI with a 24 volt system.  Your alternator charges your start batteries, and if I understand your description correctly your diesel charger charges your house batteries.  I assume your inverter runs from your house batteries.  You need to install a bridge between your house batteries and your start batteries so that the alternator supplies current to both when operating.  AS noted the best way to do this is with a relay, which can be manually controlled or set up for automatic switching so that you can isolate your starts from your house batteries when desired.  I went simple with a marine style A-B-A+B battery switch, and manually connect the house batteries to the starts when I want to run the inverter on the road.  It works smooth as silk, btw.  I highly recommend it.

The inverter will draw roughly 150 amps at 12 volts nominal to operate the AC unit, and roughly 230 amps to start it.  Actual operation is a little less since the alternator is putting out 14 volts usually.  Cable requirement is up there around 4/0, but I didn't bother to look it up.   You need big cables, anyway.

What was your thought process on going with the diesel battery charger, if I could ask?  I am strongly considering building one as my generator when the time comes to do a built in gennie.

Brian

[Lee Bradley]

...or add a small alternator (80-100 amps) to charge the start batteries and use the 50DN to charge the house batteries. Also add a three stage charging regulator to control the 50DN.

[buddydawg]

My bus has 2 alternators, the 50DN and a small belt driven one.  It came from the facory that way.  I have never determined what the other one is for, one day I'll trace it down.  I have been thinking about using the 50 to run my air over the road, just another in a long list of things I'd like to do.

[travlinman]

Hey Guys,

OK, so it is possible to run the roof air off my inverter via the 50 DN. But, I have a concern. As I understand the Wrico set up it involves using the house batteries and there in lies the problem. I have AGM 4D batteries and they like to be charged to 14.4 volts while my start batteries like 13.4 volts and that is where the engine regulator is set. So will I be harming my AGMs? I would think so. That is why I think I would need to run the roof air off my start batteries. Thoughts?

Brian - The idea behind the DBC was simple. I rarely plug my bus in so I have all 12 volt appliances. Fridge, lights, stereo etc. The only thing that is 110 is the roof air and with the capacity of new inverters I can run that without a generator. So I went with the DBC. I also like the higher charge rate of the DBC vs a generator.

TM

[bevans6]

The AGM's can take the higher charge, but I've never heard of them being harmed by a lower charge.  You'll be charging them normally often enough anyway, I don't see a problem.  I think your start batteries can take a higher charge as well, 13.4 seems quite low.  Maybe good for indefinite maintenance charging, but not for replenishing start batteries.  My wet cell starts are charged at 27.5, so more like 13.8 volts.

My bus is almost all 12 volt as well, for the house stuff, and I like the idea of the DC generator a lot.  i have the 3,000 watt inverter for anything that needs AC.

[Sean]

... I have AGM 4D batteries and they like to be charged to 14.4 volts while my start batteries like 13.4 volts and that is where the engine regulator is set. So will I be harming my AGMs? I would think so. ...

No, you will not harm the AGMs, so long as you also periodically charge them with a quality three-stage charger.

The 14.4 figure is a "bulk charge" rate.  If you look at the detailed specifications you will find that the "float" rate is substantially lower, probably around 13.4-13.8.

BTW I, too, think that 13.4 is too low even for your start batteries.  Where did you get that number?

Note that in the configuration you propose, the batteries are not involved in running the air conditioner.  The resting battery voltage will be no higher than about 12.8 volts even when fully charged; with your alternator regulated to 13.4, power will flow directly from the alternator to the inverter.  Some power will also flow from the alternator to the batteries.  No power will flow from the batteries to the inverter.

HTH,

-Sean
http://OurOdyssey.BlogSpot.com

[travlinman]

OK sweet, now I am getting my head around this, sounds like it is very possible.

Thanks everyone for your thoughts.

On to the nitty gritty. My '06 is already converted so running any additional wiring could be difficult. That being said I may have all the big pieces in place. Here is what I've got.

50dn Alternator
Big cable running from the alternator to the start batteries.
Smaller cable running from the start batteries to the inverter bay. This cable terminates in the inverter bay at a stud. Another cable then runs up to power the dash.
Across the bus accessable by a chase are the house batteries.

Sean, I could be wrong about the start battery voltage. This is not my strong suit but I am enjoying learning. What would a correct charge set point be for the 50dn with two 8D lead acid start batteries?

I can shoot photos if anyone wants to help walk me through this.

TM

[Sean]

...
Big cable running from the alternator to the start batteries.
Smaller cable running from the start batteries to the inverter bay. This cable terminates in the inverter bay at a stud. Another cable then runs up to power the dash.
Across the bus accessable by a chase are the house batteries.
...

If you intend to charge your house system or run house loads such as the air conditioner from the main alternator, the cabling from the start batteries to the house system must be adequately sized for the total draw.  The 50DN on your 4106 is capable of producing around 300 amps, and, once the chassis batteries are fully charged and all chassis loads are accounted for, you could possibly have 250 amps or more available for the house system.  That requires a minimum of 000 cable.  I recommend you separate the house and chassis systems with a 300-amp solenoid rated for continuous duty and to break that amount of current.

Sean, I could be wrong about the start battery voltage. This is not my strong suit but I am enjoying learning. What would a correct charge set point be for the 50dn with two 8D lead acid start batteries?

Generally flooded lead-acid batteries should have a vehicle charging system set point of 13.8-14.0 volts.  To set properly, you should measure that voltage right at the battery terminals with the engine running at operating RPM (say, 1,600 RPM) and the "normal" accessories running.  That being said, the best setting to use is always the one specified by the manufacturer of the battery.  If you have, say, an Exide starting battery, you should go to Exide's web site and look up the specification.

Bill Darden's excellent battery web site is, IMO, required reading for every bus nut.  Read it cover to cover:
http://batteryfaq.org/

Additional information on car batteries can be found here:
http://www.landiss.com/battery.htm

HTH,

-Sean
http://OurOdyssey.BlogSpot.com