| Author |
Message |
Stephen Fessenden (Sffess) (63.25.54.129)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, January 08, 2002 - 11:55 pm: | |
The question of using a 24 to 12 volt DC-DC converter or a (Vanner) equalizer has come up several times. For the bus lighting system I just calculated that with high power halogen back up lights and head lights and running and tail lights on the 12 volts all on at once will require 45 Amps or more. There are converters bigger than that. But what if you want to start your generator from your bus 12 volt terminal? Can't do that through the converter and without an equalizer you just messed up the balance between the batteries.
Now the worst senario:
Picture yourself at night trying to back onto a side road from a highway to turn around. You have on your lights and your back up lights all powered through a DC-DC converter. For some reason the circuit breaker on the converter blows and all your lights go out. The lights of a semi come over the hill and you switch on inside RV lights hoping he sees you.
A converter in that situation, though very reliable, runs all the lights through a single possible failure point. If you had used an equalizer all the lighting circuits would have come directly off the 12 volt terminal, each circuit through its own breaker. High and low beams are on different breakers so you wouldn't lose both from one failure. If the converter itself fails you have no bus lights. If the equalizer fails you run on to a convenient stopping point, maybe home, and then fix it.
Steve Fessenden
Steve Fessenden |
jmaxwell (66.42.93.81)
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Votes: 0 (Vote!) | | Posted on Wednesday, January 09, 2002 - 12:54 am: | |
Steve: Forget the tractor-trailer rig, cuz everybody knows u can't back off the main road onto a side road with the tow'd back there. And, if u already got it off, park it in the road with the emergency flashers on until u get back onto the side road, where u can safely spend the night till the sun comes up and u don't need running lights. |
Richard Bowyer (Drivingmisslazy) (65.207.109.129)
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Votes: 0 (Vote!) | | Posted on Wednesday, January 09, 2002 - 6:15 am: | |
Steve, how about a little bit more explaination about the actual difference between a 24 volt to 12 volt converter, and a Vanner equalizer.
Richard |
Steven Gibbs (12.148.43.6)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, January 09, 2002 - 6:45 am: | |
Richard,
An equalizer simply allows you to use a 12 volt source that is already on your bus -- the positive terminal connected to the negative terminal in the series battery configuration.
How much power you decide to pull off this is dependant on the size wire you run to your 12 volt loads and how large your equalizer is.
The equalizer does not perform any task in providing this load. Since some of the charge current from your alt is not making it to the second battery, because you are taking it off for other uses, the equalizer simply makes sure (don't know how) that both batteries receive a full charge.
Your equalizer sizing would be dependant on how much continuous load you would expect to pull off the battery while your cable sizing will determine how much max or intermintent load you could pull.
Da' book (MCI 9 manual) describes two ways that the factory set up 12vdc sources for the coach. In the first, up to 10 amps could be taken directly off of the batteries without an equalizer but it is recommended that the batteries be rotated regularly to even out the wear. This sounds like rotating the tires around a bad alignment to allow all tires to wear out (prematurely) at once.
In the other option, the factory provides an equalizer to provide up to 60 amps of balancing between the batteries and rotation is not required.
I would not recommend that you supply your house 12 volt loads in this manner. A house battery system is a must. However, not only are your headlights 12 volt but during the conversion process you will likely want to and many other little toys (like cruise control, remote mirrors, radios, GPS, fans, etc.) that are easier to get in 12 volt. These road-use loads should come from your coach power. You can also tap this 12 volt source to provide some charging current to your house battery bank.
Finally, (yes I do intend to wrap this long winded response up). If you are planning to run air conditioners off of the inverter while running down the road and have that big alternator relenish the batteries, Wrico recommends a 24 volt house system and inverter setup because you will be better matched and not need to worry about equalizing that large of a load. Of course, you still would use an equalizer so that you can get the 12 volt source for smaller coach loads (which is what you were after in the first place).
Steve Gibbs |
Richard Bowyer (Drivingmisslazy) (65.207.109.52)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, January 09, 2002 - 9:48 am: | |
Thanks, Steve. I have never had a 24 volt system and was not exactly sure what the difference was.
I have been helping Al sort out his electrical problems and he has a bastard arrangement, if I ever saw one. His 12volt coach load(lights,Jake, cruise etc.) are connected to his small house battery, which also has a 120 volt to 12 volt DC charger connected to it.
I am suggesting that he get rid of the 12 volt house system and go to 24 volt so he can operate the AC unit thru the inverter from his big engine alternator. He can also charge his coach battery bank and his house battery bank from the engine alternator.
He then can operate his 12 volt coach loads thru a Vanner, and his 12 volt house loads thru a Vanner or a 24 volt to 12 volt converter.
He also has a 12 volt alternator on his engine. I am suggesting that he replace that with a AC compressor for operating a driver AC system. Sound OK to you?
Richard |
Steven Gibbs (12.148.43.7)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, January 09, 2002 - 12:04 pm: | |
Richard,
Exactly, only as Steve Fressenden says, use the Vanner rather than a 24 to 12 converter. Your friends coach does sound like it needs to be reworked.
Steve |
Richard Bowyer (Drivingmisslazy) (65.207.109.148)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, January 09, 2002 - 12:31 pm: | |
OK. Now where do we find a couple of used Vanners, reasonably priced? |
Stephen Fessenden (Sffess) (63.27.88.28)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, January 09, 2002 - 11:39 pm: | |
Vanners up to 60 Amps are not expensive enough new to worry about finding used ones. Try the Ohio distributor listed on Vanner's website. Call Vanner directly with your questions then call a distributor and order one at a discount. You may have to use a business name. Hey a ficticious name for a business costs $35 every five years in Florida. You don't have to do any of the business tax paperwork as long as you pay the required sales taxes on each purchase to the supplier.
Some city or highway coaches had 100 Amp Vanner equalizers to allow running a 12 volt wheelchair lift. May be a source of used ones.
Steve Fessenden |
Stephen Fessenden (Sffess) (63.27.88.28)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, January 09, 2002 - 11:50 pm: | |
Richard,
I suggested to Al that he have the 12 volt alternator converted to 24 volt or buy a 24 volt alternator of the same size. That would give him separate 24 volt charging systems for house and engine batteries. He could interconnect batteries between systems if one alternator failed and charge them all together. Otherwise the systems would be completely separate and he would always have a spare alternator. Thats the system I have now and it is great.
Would be nice to have Drivers A/C though.
Steve Fessenden |
Stephen Fessenden (Sffess) (63.27.88.28)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, January 10, 2002 - 12:01 am: | |
Steven,
Great post on how an equalizer works.
It works whether the batteries are being charged or they discharging or just sitting.
There are three connections: 24 Volt battery terminal (fused), 12 Volt battery terminal (fused), negative (ground) battery terminal.
The equalizer continuously monitors the 12 volt and 24 volt terminal voltages and charges the 12 volt terminal from the 24 volt terminal to keep the voltage exactly half of the 24 volt terminal voltage (within .05 volt). The standby current draw is minimal and the losses are very low.
You can, if needed, draw all of the power of the full 24 volt system through the 12 volt terminal.
Steve Fessenden |
Richard Bowyer (Drivingmisslazy) (65.207.109.160)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, January 10, 2002 - 12:04 am: | |
A good idea if he does not put in drivers air. I am afraid that with only one AC in a 35 ft bus, he will get uncomfortably warm in the Southern California climate. And even more so it he ventures into Nevada or Arizona.
Richard
BTW, what part of Florida are you in? |
Steven Gibbs (12.148.43.7)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, January 11, 2002 - 6:32 am: | |
Steve F.,
Thanks for the explanation of how the balancing occurs.
One thing I noticed in Da Book in large, bold print was a warning to disconnect the equalizer prior to arc welding on the bus.
Also there is a specific sequence for unhooking and reconnecting a to the batteries.
I'm sure you're aware of these two items, FYI for others less familiar.
Thanks,
Steve G. |