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Old 03-08-2011, 06:29   #46
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Re: Battery Isolator with Battery Drain

Nice post Maine...

Anyone arguing about flow of current in a diode being both directions is wrong. The PN junction will pass current in only the forward direction, no matter what the voltage bias level. Trying to pass current in the opposite direction forces the electron-hole pairs apart, widening the junction so no current flows. The voltage across a FORWARD biased diode is never more than the forward voltage drop of the diode, about .68v, schottky diodes aren't used for this. If you don't understand this than you shouldn't reply about this subject.

The problem...there is a path between the 2 circuits, starting and house. On page 1 Don and Geo had 2 of the very few correct, or applicable, posts on this thread. Read it over.
The starting batteries should be connected DIRECTLY to the starters. The isolator is used for the charging path. The ignition switch should operate ONLY the alternator/regulator turn on, engine gauges and the starting solenoid. If it is tapped off to some other circuit than that is your problem. The starters should NOT be connected through the isolator. It forces the engine cranking amps to go through the diodes and may burn it out. You only want to put charging current through the isolator.
Not sure what isolator you have...generally they are arranged so that the center terminal is the common anodes. This should be the connection to the alternator. From there one lead goes to the starting batteries...one lead goes to the house batteries. I suspect you have the isolator being used to separate the 2 starting batteries rather than the house bank. Connect the alternator sense lead to the house batteries. If you also want to isolate the 2 starting batteries from each other than you require an isolator with another diode.
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Old 03-08-2011, 07:23   #47
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Re: Battery Isolator with Battery Drain

I don't understand, but I'm replying anyway.

From Victron:
Argo Diode Battery Isolators - Victron Energy

Low voltage drop due to the use of high efficiency Schottky diodes.

Quote:
Originally Posted by Kapena View Post
Nice post Maine...

Anyone arguing about flow of current in a diode being both directions is wrong. The PN junction will pass current in only the forward direction, no matter what the voltage bias level. Trying to pass current in the opposite direction forces the electron-hole pairs apart, widening the junction so no current flows. The voltage across a FORWARD biased diode is never more than the forward voltage drop of the diode, about .68v, schottky diodes aren't used for this. If you don't understand this than you shouldn't reply about this subject.

The problem...there is a path between the 2 circuits, starting and house. On page 1 Don and Geo had 2 of the very few correct, or applicable, posts on this thread. Read it over.
The starting batteries should be connected DIRECTLY to the starters. The isolator is used for the charging path. The ignition switch should operate ONLY the alternator/regulator turn on, engine gauges and the starting solenoid. If it is tapped off to some other circuit than that is your problem. The starters should NOT be connected through the isolator. It forces the engine cranking amps to go through the diodes and may burn it out. You only want to put charging current through the isolator.
Not sure what isolator you have...generally they are arranged so that the center terminal is the common anodes. This should be the connection to the alternator. From there one lead goes to the starting batteries...one lead goes to the house batteries. I suspect you have the isolator being used to separate the 2 starting batteries rather than the house bank. Connect the alternator sense lead to the house batteries. If you also want to isolate the 2 starting batteries from each other than you require an isolator with another diode.
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Old 03-08-2011, 09:41   #48
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Quote:
Originally Posted by nigelmercier
charge to one, and decrease it to the other. I wasn't trying to assert that there are two currents in opposite directions, just that there are two vectors involved.
Heh. As I figured. He's being "academic". Yes it is the same as the government saying a $10 tax deduction puts money in your pocket. But it sure seems like the money is flowing towards the government.
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Old 03-08-2011, 16:37   #49
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Re: Battery Isolator with Battery Drain

Ref #35 I should have included the prob. need for a connection from the starter relay/solenoid circuit to supply excitation for the alternator. (Seniors moment)

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Old 03-08-2011, 17:36   #50
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Re: Battery Isolator with Battery Drain

cal40john...Absolutely correct...I should not have written about the schottky not being used. Good catch.
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Old 03-08-2011, 18:02   #51
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Re: Battery Isolator with Battery Drain

Kapena You were just testing to see if we picked it up. own up!!
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Old 03-08-2011, 23:43   #52
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Re: Battery Isolator with Battery Drain

Quote:
Originally Posted by Kapena View Post
The PN junction will pass current in only the forward direction, no matter what the voltage bias level. Trying to pass current in the opposite direction forces the electron-hole pairs apart, widening the junction so no current flows.
With one slight alteration, I fully agree: Trying to pass [a net] current in the opposite direction ...

Let's go through this is stages:

When the diodes are forward biased they become low resistance. This then provides a low resistance path between the two batteries. Checkpoint #1 - everyone with me so far?

As a result of this low resistance, a current will flow that tends to equalise the battery voltages. The diodes are still on (low resistance), so this is inevitable. The batteries can both "see" a different potential. Checkpoint #2 - a more difficult concept perhaps, bear with me if this doesn't seem right to you.

This current will alter the distribution of the incoming charging current. Obviously, if this current was greater than the incoming current, the diodes will switch off, but the incoming current is higher. Checkpoint #3 - everyone understand now?
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Old 04-08-2011, 04:41   #53
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Re: Battery Isolator with Battery Drain

seems some are more intersted in winning the technical battle than helping the OP with their problem, which has pretty much gotten lost on the thread
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Old 04-08-2011, 06:59   #54
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Re: Battery Isolator with Battery Drain

Yes, unfortunately so has the OP, it seems, and I don't blame him.
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Old 04-08-2011, 09:20   #55
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Re: Battery Isolator with Battery Drain

Quote:
Originally Posted by Don Lucas View Post
seems some are more intersted in winning the technical battle than helping the OP with their problem, which has pretty much gotten lost on the thread
Quote:
Originally Posted by DeepFrz View Post
Yes, unfortunately so has the OP, it seems, and I don't blame him.
Post 7 OP is asked for make and model. Post 12 OP says he will get back maybe on Monday with info. Maybe he didn't make it to the boat and will post when he does. Meanwhile discussion as to how electronics really works ensues.

OK on topic, here is a guess, a Sure Power 2703 fits the bill. It has 5 posts. Two of them are labeled Alt 1 and Alt 2. The others are labeled 1, 2, 3. Pretty hard to wire that wrong. Disconnect and use a DVM set to diode test and check all posts between alt and bat. Should read open with leads in one direction and somewhere between 0.3 and 1.4 (or 300 to 1400, depends on whether meter shows mVolt or volt drop) with the leads reversed. If so then there nothing wrong with the isolator and there pretty much has to be a wiring problem somewhere else.

Look at the diagram on the bottom right of page 2:
http://www.grampianowners.com/Links/...lator_Inst.pdf

Figure 3:
http://www.cooperindustries.com/cont...ST_180119a.pdf

BACK to esoteric discussions. I couldn't find a diagram for the Sure power. Do you think that there are 2 diode drops in this thing? One set of diodes to isolate the alternators, then another set to distribute the now combined power to the individual batteries?

John
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Old 04-08-2011, 10:00   #56
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Re: Battery Isolator with Battery Drain

LOL...should electrical questions be grouped with political discussions as off-limits topics?
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Old 10-08-2011, 20:10   #57
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Ok, I'm back. Thank you all for your replies. I just spent an hour trying to catch all of you up on everything I have been trying. As I was just finishing writing the post script, my browser unexpectedly shut and the entire post was deleted. It's getting late for me, so I can't re-write it now. However, stay tuned as tomorrow (after I finish a new experiment) I will make time to re-write what I wrote.

Thank you in advance for your patience. I gained many insights from all the posted I have read.

Ben Sigler
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Old 06-09-2011, 11:41   #58
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Re: Battery Isolator with Battery Drain

Ok, so here it goes; I know a lot of water has been under the bridge (pun) since the last time we spoke.

In light of a hugely long post, I have something strange to tell you. As a last ditch effort, I called in a marine electrics specialist who tested the isolator and told me it was not working. He also tested my charging system and told me both the alternators and one of the batteries were not working. In light of his tests, I removed the entire electrical system from the boat (alternator, batteries, chargers, wires, the whole deal!!) and tested everything myself. One of the batteries were problematic, but the isolator was fine, so were the alternators (factory tested).

So here's the crazy thing, I put everything back together and it just started working. For the life of me, I can't figure out why. Before I took everything apart, I labelled where everything came from and put it all back the same way.

I know there is not much to comment on this, but I can't figure it out. The only thing that was changed when I reinstalled everything was the one starter battery.

go figure. Any theories????
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Old 06-09-2011, 12:03   #59
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Re: Battery Isolator with Battery Drain

Bad ground somewhere, due to surface corrosion, poor connector, or loose terminals.
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Old 06-09-2011, 16:40   #60
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Re: Battery Isolator with Battery Drain

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Originally Posted by btrayfors View Post
Bad ground somewhere, due to surface corrosion, poor connector, or loose terminals.
That's my bet.
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