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Old 04-15-2017, 02:16 PM   #1
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Question Setting up Battery isolator - Alternator problem?

Hi Guys,

In need for help, I'm stuck.
I'm trying to set-up a battery isolator on my bus , the diode kind, a Sure Power 200A 1 input 2 output. My engine is a T444E.
So here is my problem: without the isolator, my engine batteries read a nice 12.7 V. When turning the engine on, the voltage only increases to 14.1 V. The value is a little low I believe, and I'm also concerned because it reaches 14.1 V after 1 min, right after turning the engine on, I read 12.5, which slowly increases to 14.1. So first question, should I be worried about that?

Now when I install the isolator, I connect the alternator + to the isolator input, and batteries to the first output of the isolator. When engine off, batteries are still at 12.7 V, but when I turn the engine on, I only get 12.5V. So I checked on the alternator, and I only read 0.7 V. So it seems that the alternator is not doing its job when the isolator is installed, but I just don't understand why. Any idea? Any help would be very much appreciated.

Cheers!
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Old 04-16-2017, 07:56 PM   #2
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The diodes are starving the alternator's internal regulator of the voltage it requires to excite the alternator. You need to use an isolator with an alternator excitation provision. The best out there is the Perfect Switch battery isolator, but it's not cheap. You have a cheap battery isolator as it has a voltage drop of .7 which is terrible, and it apparently isn't the correct configuration for your alternator as there's no excitation provision.
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Old 04-18-2017, 10:38 AM   #3
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Hey guys, I'm working with the Monx on the same bus. Thanks for your help JumpShowHigh.

So basically here is how I understand the problem we have:
we have an alternator with an internal regulator, with 1 wire coming from the battery serving as an input for the internal regulator and an output for charging the battery. When we add the isolator, the current can flow only in one direction, to charge the battery, but the internal regulator don't get any current from the battery because of the isolator diode blocking it, therefore electro-magnet is not on, so no charging when engine on.

So ideally we would need a isolator with an exciter, but we dont. Could we provide the current for the internal regulator from another source? Like the ignition?
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Old 04-18-2017, 11:22 AM   #4
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Possibly, if you have a different type of regulator, but it's been my experience that that the path of least resistance is to either go to an external regulator, or change to an isolator configuration suitable for the regulator you currently have.
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Old 04-18-2017, 06:09 PM   #5
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So here is my problem: without the isolator, my engine batteries read a nice 12.7 V. When turning the engine on, the voltage only increases to 14.1 V. The value is a little low I believe, and I'm also concerned because it reaches 14.1 V after 1 min, right after turning the engine on, I read 12.5, which slowly increases to 14.1. So first question, should I be worried about that?

That part seems normal to me. The regulator takes a few seconds to determine what if any output is needed.

The next part I don't get. Have you come off the alternator positive with the wire going normally to the battery and taken it to the isolator input? If so that is right.
Then the two lower terminals are for battery A and battery B, not both batteries on the same output terminal. Then the isolator will charge both batteries through the alternator.
Hope this helps.
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Old 04-19-2017, 12:01 PM   #6
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Hey BlackJohn,

thanks for your help.
yes that's what I did. But it doesnt work, when I do what you said, the alternator doens't generate any current. It seems that it's because the alternator needs to get first current from the battery to active its electro-magnet, only then it provides currents. Therefore with the diode from the isolator, no current can reach the alternator, that's why some isolators have a 4th terminal to provide this current to the alternator.

Now, I'm trying to see how I could excite the alternator from another source, I'm not even sure it's possible.
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Old 04-19-2017, 01:21 PM   #7
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Ok so where is the power coming from for the alternator without the isolator?

Most have a separate connector to feed the exciter. Yours doesn't?
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Old 04-19-2017, 02:03 PM   #8
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theres a lot of alternators out there that are '1 wire' and have no ability to use an external Sense voltage... these self-excite at a specified RPM... many of them its as high as 1800 Alternator RPM (not engine RPM).. some of the better ones are 1200.

on my DEV bus, its a Bosch SB200 which has an external Sense and an Excite lead..
I found that if I connected the Excite lead directly to a battery, I would carry a pretty decent parasitic load because the alternator field stayed excited...

what I then did was install a relay between the battery and the excite Lead.. ( I wasnt sure if i should grab a standard Ignition feed)... once i did that then the alternator excites upon key-on, my Sense Lead is connected by Fuse directly to the Battery..

my isolator is designed to not engage the solenoid unless its detected voltage is 12.9 or higher... thus you wont kill your main batteries if you key-on without start and your house batteries are Dead. it also has a manual input on it so if I did want to involve the house batteries without engine run I can.
-Christopher
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Old 04-21-2017, 11:36 AM   #9
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Hey guys, thank you all for your help on this matter, appreciate it!

So my alternator is a Wilson SI22. It has 4 terminals, bat, negative, I and R. I just called the company, they told me that I can plug the ignition to the I terminal, which would excite the alternator and fix my problem. R is for accessories, not sure what exactly.

I'll try that and let you guys know how it went. Kind of new to this, so I'm not exactly sure how what's the proper way to find the ignition wire, probably not that hard but advises are welcome
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Old 04-21-2017, 11:58 AM   #10
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interesting, they dont have a S and I terminal.. 'S' was the Sense lead driect from battery to sense the battery..

'I' is for ignition (excites the field)...

they must get the sense from the ignition lead.. interesting..

-Christopher
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