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RJmule (Rjmule)
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Username: Rjmule

Post Number: 59
Registered: 2-2007
Posted From: 75.51.69.155

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Posted on Thursday, April 26, 2007 - 1:48 pm:   

The difference in whether to use a battery isolator or battery separator will depend on whether your alternator has internal or external voltage sensing. Many of the newer alternators are internal sensing and so cannot be used with an isolator, because of the loss of approximately 1 volt across the diodes, In these cases you would use a battery separator. The experts at Smith Auto Electric can determine which unit you will need.
any one know which one would be used for my application. Joel in havasu has an isolator he offered to sell me but when i went online to look at his product I was thrown a curve ball. Thank all. RJmule. Randall
Buswarrior (Buswarrior)
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Username: Buswarrior

Post Number: 999
Registered: 12-2000
Posted From: 74.12.88.110

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Posted on Thursday, April 26, 2007 - 3:38 pm:   

Hi RJ,

My bias is to use the seperation strategy. Relays or switches depending on your budget, and/or forgetfulness to use the switches!

Isolators at the proper amperage aren't cheap, and as you noted, there is voltage drop associated with them which will keep the protected batteries from achieving the desired charge. Again, you may compensate for that through the other methods of operation that YOU will decide upon.

There are busnuts who have chosen the same battery types for both start and house sets so that connecting them all together for charging purposes causes little trouble.

All depends on your expected duty cycle, and how much fun you want to have in the complexity department!

happy coaching!
buswarrior
Richard Bowyer (Drivingmisslazy)
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Username: Drivingmisslazy

Post Number: 1888
Registered: 1-2001
Posted From: 75.108.78.129

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Posted on Thursday, April 26, 2007 - 5:15 pm:   

I just adjusted my alternator output using the voltage regulator adjustment to get the proper charge voltage at the battery itself, after the isolator. Worked great for many years.
Richard
RJmule (Rjmule)
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Username: Rjmule

Post Number: 63
Registered: 2-2007
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Posted on Friday, April 27, 2007 - 12:06 am:   

Thanks Richard and Mr. Warrior, Great Info. The price was Great from Joel for a 300 amp Isolator so i didnt think i could go wrong. Thanks Again. RJmule- Randall
George M. Todd (George_mc6)
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Username: George_mc6

Post Number: 135
Registered: 8-2006
Posted From: 76.80.194.89

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Posted on Friday, April 27, 2007 - 12:41 am:   

We were just here a few days ago, and maybe I can explain a diode seperator a little differently again? Voltage drop across silicon diode material is 0.6 Volts. That means that at 100 amps thru the separator, (which is a LOT) the power lost would be 60 watts. One electrical horsepower is about 743 Watts I think, so the total loss at 100 amps is about 1/12 of one horsepower!!! Once again, the battery terminal on most of our bus alternator's regulator is connected to the master switch, as it must be turned off when the engine is not running, or the regulator will discharge the starting batteries by putting full field current thru the alternator, trying to get its voltage setting out of a stopped alternator. The regulator has no idea whether the engine is running or not, it just puts out field current at the level needed to keep the battery voltage at the level it is set at. Now, the alternator OUTPUT cable is connected to a larger cable running between the battery switch and the starter, and another splice is made in that circuit to take power forward to the master switch and the central junction box, etc. The seperator is placed electrically in the alternator output cable, which means that the regulator BATTERY terminal SEES VOLTAGE AFTER IT HAS BEEN THRU THE SEPERATOR, and the master switch, etc! This means that no regulator adjustment is necessary to acheive the same charge rate, or operating voltage, because the regulator keeps the voltage at its setting, and has no idea that the voltage drop from back to front has increased by 6/10 V.
The reason a diode seperator has two diodes, (one for start, and one for house) is to keep the drop and charge rate even. One diode in the coach circuit would keep the house circuit from discharging the start batts, but then the house batts would always get 0.6 V more...
Whew,
George

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