Battery Isolator: What is wrong with this picture?

[straygoose]

OK I rewired the whole mess. Here is what it looks like now.





Nice fresh 6awg wires and marine fittings! Woo-Hoo, definitely overkill, but that's all the store had. One line runs from the alternator output post to post "A" in the isolator and the other runs back across the engine compartment to re-connect to the original alternator output lead.Everything seems to be charging OK, but I got some strange readings when I went to measure the output voltages and when I tested the isolator for continuity.

Battery Charging:

Engine Battery

Static = 12.38v Running = 14.24v After 10 min. run = 12.48v

I think my engine battery is slowly fading out. I need to get her on a load tester next time I'm in town. She should be holding about 12.8v. AGM batteries are overrated, if you ask me. This one is my third. The first lasted all of 8 months and the second blew a vent cap while driving between Philly and DC one day. This one has lasted about 16 months or so. I'm going back to the old-fashioned lead acid job just as soon as I know for sure.

House Battery:

Static = 12.65 Running = 13.43 After 10 min. run = 12.78

Looks like the house side charged right up! This is great, but it makes the next set of voltage readings very confusing.

Voltages thru Isolator:

Post "A"> Post #1 = 0.04v ???

A>2 = .08v ???

Shouldn't these be pretty close to the alternator output (~14.4v)?

Isolator continuity:

A>1 = continuity

A>2 = open ???

1>2 = open

Why is A>2 open?

BTW I did these measurements several times, reversing the test leads back and forth and got the same readings every time, so I'm sure it's not a mis-read.

Anyway, I can't seem to get a handle on whether the isolator is good or bad, so I'm just going to spend $35 for a new one and get it over with. Only problem is, there isn't one within a hundred miles of me right now, so its going to be a few days while I wait to have one mailed to my PO box.

I thought about going to the solenoid, but it seems like more trouble than its worth at this point. This is a 1989 Falcon Class B. She's a great little vehicle, but her wiring is old-school Ford, with an external starter solenoid and voltage regulator, so changing over to the mechanical system may be more work than its worth.

I still don't have a clue what the mystery switch does, and neither does anyone else that looked at it. However, I am about 99% certain that it is connected to the isolator. I am going to put out another post in the Vintage RV section and see if any other Intervec owners have any ideas.

[ahicks]

Originally Posted by straygoose

OK I rewired the whole mess. Here is what it looks like now.


Battery Charging:

Engine Battery

Static = 12.38v Running = 14.24v After 10 min. run = 12.48v

I think my engine battery is slowly fading out. I need to get her on a load tester next time I'm in town. She should be holding about 12.8v. AGM batteries are overrated, if you ask me. This one is my third. The first lasted all of 8 months and the second blew a vent cap while driving between Philly and DC one day. This one has lasted about 16 months or so. I'm going back to the old-fashioned lead acid job just as soon as I know for sure.

House Battery:

Static = 12.65 Running = 13.43 After 10 min. run = 12.78

Looks like the house side charged right up! This is great, but it makes the next set of voltage readings very confusing.

Voltages thru Isolator:

Post "A"> Post #1 = 0.04v ???

A>2 = .08v ???

Shouldn't these be pretty close to the alternator output (~14.4v)?

Isolator continuity:

A>1 = continuity

A>2 = open ???

1>2 = open

Why is A>2 open?

BTW I did these measurements several times, reversing the test leads back and forth and got the same readings every time, so I'm sure it's not a mis-read.

Anyway, I can't seem to get a handle on whether the isolator is good or bad, so I'm just going to spend $35 for a new one and get it over with. Only problem is, there isn't one within a hundred miles of me right now, so its going to be a few days while I wait to have one mailed to my PO box.

I thought about going to the solenoid, but it seems like more trouble than its worth at this point. This is a 1989 Falcon Class B. She's a great little vehicle, but her wiring is old-school Ford, with an external starter solenoid and voltage regulator, so changing over to the mechanical system may be more work than its worth.

I still don't have a clue what the mystery switch does, and neither does anyone else that looked at it. However, I am about 99% certain that it is connected to the isolator. I am going to put out another post in the Vintage RV section and see if any other Intervec owners have any ideas.

Regarding voltage through iso. If the engine isn't running, and the batteries are disconnected from it (posts#1 and #2) there's not going to be any voltage when measured at #1 or #2. That's the easy part here.

Where I'm stumped is how you're getting the continuity test on the #2 terminal that you are (which indicates you have a bad iso. due to open/faulty diode that supposed to be feeding #2) yet you indicate the aux. battery appears to have built up some charge after a 10 minute run? The only thing I can think of is the battery is being charged through some other path. I can assure you, that if there is no continuity "A" to #2, the isolator is not supplying charge current through that post.

Regarding your switch. There are 3 terminals on that isolator - and willing to bet none will lead to that switch. Therefore, that switch has nothing to do with the isolator?

Now, that said, the switch may have something to do with that aux battery getting it's charge? Dunno. You haven't supplied any/enough info to even have a best guess there. Wish I could be more help on that...

[straygoose]

I'm thinking the batter is getting charged from elsewhere too, but I'll be darned if I can find out how and where. I traced the lines from the house batt back and got as far as the charger mounted underneath my closet space. After that, I lose the trail, unless I want to take my bathroom apart. :(

If you look close at the first iso pic, you can see the circuit breaker right next to it, with a lead coming into it from post 2. I followed that gray wire coming out of the breaker, and to the best of my knowledge it goes thru my firewall and connects to the mystery switch.

Aaaaaannnnddd, I think I just answered my own question: If all that is coming off post 2 of the iso is that flimsy little line going to the switch, then the house battery is getting power from somewhere else. That little line is only like 12 awg, so there's no way it could handle a 90a output alternator.. Its not much more than furnace wire strength.

This also means that the isolator is irrelevant right now, since the house battery isn't hooked up to it. I need to run a line from post 2 of the iso to either the charger or the battery itself, and disconnect whatever connection is there now.

What a mess...

Actually the v measurements through the iso were with the engine running, which is why I thought they were so strange. I would assume that with no power to them they would be zero.

Oh well, looks like I need to start taking the bathroom and closet apart. I need to figure out where that house battery is getting it's power from.

[YC1]

If you start with fresh thinking. Pretend you have a water hose running from your house. That is the alternator output which you can measure with the engine running and it should be around 14 volts.

You want to fill two buckets at the same time and want to keep those buckets seperate. You install a Y adaptor (isolator) and can fill both buckets now. With the engine off the alternator is not filling the buckets and the isolator Y will not let each bucket drain the other.

Start the flow of water and measure the wires on the isolator. The one with the most voltage (pressure) is the output of the alternator. That should connect to the proper terminal of the isolator. Making an assumption it is the center top one might be a mistake but still is probably correct. Now you should measure the voltage (pressure) on each of the two other connectors. You should measure about .7 volts less than the alternator input.

If you measure less by very much the isolator is bad. In a pinch you can stack all three wires onto the same post to charge all batteries.
The thing did not look wired correctly in the first picture but I won't try to decipher that because you have too many other issues that absolutely should be fixed before anything and you have already started. You need to replace any rusted nuts and washers and clean and tighten every connection you can find. Rust is an enemy of a 12 volts system. The push of 12 volts is very weak and just cannot go through rust very well if at all.

Once all is clean start the voltage measurements again. Start at the isolator and go to each battery. You should see the same voltage on the isolator at the battery associated with that connection.

Repeating, rust is like stepping on the garden hose, it will reduce the speed at which the buckets fill.

With the poor charging don't condemn any batteries yet. Most batteries are murdered due to poor maintenance of the systems and don't die of natural causes.

[Chaffeekid]

Replaced an Isolator just like this one in my brothers old Class C. Bought the replacement at the local NAPA dealer, forget exactly what it cost, but wasn't a lot. The store didn't have one in stock but had it delivered in about 3 hours. Just FYI

Hope you get it sorted out. BTW, hope that wire to terminal 1 is not touching the case of the Isolator, it will rub through the heat shrink and short and you will buy another one.

Happy Trails
Jim

[Dave78Chief]

You will have a 0.7 Volt drop across a diode. Thats why these type of isolators have fallen into disfavor and isolator relays are more prevalent.

Start engine
First reading should be "A" (meter pos lead) to ground (meter neg lead). Should be around 14.1 VDC +- .5VDC

2nd reading - "1" (meter pos lead) to ground (meter neg lead). Should be "A" value - 0.7 VDC (i.e 14.1VDC - 0.7VDC = 13.4VDC).

3rd reading - "2" (meter pos lead) to ground (meter neg lead). Should be "A" value - 0.7 VDC (i.e 14.1VDC - 0.7VDC = 13.4VDC).

After 10 minutes the voltage should still be the same. What happens is that at first the alternator amperage output is high then tapers off as the battery is charged. The regulator in the alternator maintains the voltage level at approx 14.1VDC but regulates the current. So, if the reading at "A" to ground is dropping to 12.48 volts after 10 minutes then there is a charging problem and one of the following problems exist:
1) Internal Alternator diode is breaking down due to heat
2) Regulator is failing
3) Wiring to alternator is increasing resistance due to heat (bad connection).
4) A fusible link is increasing resistance due to heat build up. (had that happen to a friend of mine). If they are real limp and soft they are failing.
5) A battery is shorting out pulling the current down.
6) The isolator diode itself is breaking down due to heat.

You check diodes disconnected from external circuits by comparing front to back resistance measurement. They will read continuity in one direction (i.e A>1) but read open in the other (1>A) when the leads are reversed. 1>2 readings should always read open in both directions because the intent of this isolator diode is to prevent current flow from battery 1 to battery 2 or vice-versa. Therefore, you only check A to 1 and A to 2 for forward/back resistance.

Simplify the circuits to make it easier to analyze:
Move the "A" (from alternator) lead to your engine battery post "1" so that you are only checking/charging your engine battery. Completly disconnect the leads to "2". This isolates the house battery system and isolator diode which allows you to just concentrate on chassis system to see if it is OK (remains at 14.1 volts at ALL times; start, 10 minutes, 1 hour, etc.). If that checks out, stop engine and move the "A" lead back to the "A" post with the "2" leads still disconnected. Start engine and verify the "A" to "1" section of the isolator is OK ("A" = 14.1VDC and "1" = 13.4VDC. If that is OK, monitor the voltage at "2" with those leads still disconnected. In an open circuit, in this case "2" the voltage at "2" should track with what you see at "A" (14.1VDC). The 0.7VDC drop across the diode only occurs at "2" when it has a load (battery) connected to it. Stop engine then connect "2" leads. Start engine and verify "2" stays at 13.4VDC.

Dave

[ahicks]

straygoose, hope you got all that!

Dave, You have more patience than I do...you put some thought into that. Nice job! We both have the same opinion of these too. I'll work on them, but really discourage replacing them with another. -Al