Current loss across battery isolator

[kastein]

Diodes work off resistance. Remember the old tubes in radios and TVs? They were full of diodes. Once they heat up, they limit the current and then the amount of heat that is released. If he is trying to run something off it, which is what I take him to say, and if his symptoms are accurate, then it is doing what it is supposed to do and he is exceeding the design of it. Most isolators are supposed to isolate a battery from the charging circuit so that you control the battery voltage for each battery. If he is only getting 30A out of it it will not be enough to run the vehicle, which is why it is stalling.

As stated above, I am making some assumptions about how he is running it. That is why I asked for a detailed explanation of how it is wired and what type of batteries etc.

as an EE I would disagree with this.

tubes were more like a MOSFET than a diode - just one that happens to have a heater / light bulb built into it. Many specialized ones for power RF transmission and demodulation have more than one grid, up to 7 in the case of some heptagrid converter tubes.

Diodes do not work off resistance, they allow current to flow in only one direction and have a forward voltage directly related to the junction temperature, a physical constant (whose value depends on the material used to create the diode, germanium, silicon, gallium arsenide, indium gallium aluminum phosphide, etc), and forward current, see Shockley's Diode Equation for more details.

However that is neither here nor there, since the regulator in a 2001 is controlled by the PCM, which uses as feedback the voltage it sees on its power lines (which come after the diode isolator in his setup) the regulator will be cranking up the field voltage on the alternator a bit to compensate for the minor forward voltage drop of the diode isolator, so the battery SHOULD be receiving full charging voltage and whatever current it requires. The way it does it with the vehicle off as well makes me think this is entirely unrelated to the isolator and is probably a corroded terminal or loose connection somewhere.

EDIT: also - if I am understanding it correctly the purpose of the isolator in this case is to separate the two batteries but charge them both via the alternator, i.e. discharging one battery fully will not affect the other.

 

[4.3LXJ]

as an EE I would disagree with this.

tubes were more like a MOSFET than a diode - just one that happens to have a heater / light bulb built into it.

Not wanting to start a fight here, but the first "tube" in those devices was the diode to change AC to DC

But be that as it may, we still do not know how he has it hooked up.

 

[Pelican]

If I'm not mistaken, vacuum tubes that we are discussing here ARE diodes, typically with one or more grids to modulate the flow of electrons to achieve some practical result.

It might be slightly misleading to say that they were "full of diodes" but some tubes had at least two distinctive elements. And, of course, some tubes were just pure diodes without control grids.

 

[kastein]

A diode with a grid is no longer a diode, it is a triode and analogous to a modern IGBT, MOSFET, or BJT. Calling it a diode with a grid is like calling a 4 stroke motor a 2 stroke motor with some changes, it is technically true but does nothing but muddy the discussion and confuse everything.

Regardless... the diodes in the isolator are not acting as resistors, they are acting as diodes, and I would put money on the isolator not being the issue here.

 

[Pelican]

With the addition of one or more grids, the tube package description becomes "triode" or "pentode" or whatever but the basic function remains that of a current flowing in one direction created by two elements acting as a diode. What one does to make that current useful might be compared to the function of a transistor or MOSFET or.... I'm not an EE but I do know something about outboard motors. LOL

Perhaps a discussion of semantics here but I agree that it adds absolutely nothing to to the problem at hand. I also agree that it appears such problem has nothing to do with the isolator as such.

 

[old_man]

It is always hilarious to listen to people who think they understand electronics try to explain how something works. A tube is sometimes called a diode in Europe, but rarely here in the US, especially since they haven't been in wide spread use in 40 years.

I've been an engineer since tubes were around. kastein is correct in what he says.

 

[Pelican]

Hilarious as it may be, in the literal sense, I was playing with vacuum tubes before you were born. I did not say that vacuum tubes are called diodes, I said that they function as diodes. I built my first scratch built tube project (reel to reel tape recorder) in 1957 just after finishing two years in pre-EE at Rice. I did not get along with calculus and ended up with a useless, as such, psychology degree. This does not in any way, shape or form make me even close to being an electrical engineer, however, I would suggest that it does not take an EE degree to understand things electrical and electronic and to so suggest smacks of sheer arrogance in my humble opinion.

I pretty much get my electrical jollies now wiring houses and Jeeps.

Now that I've said all that, Kastein probably won't sell me a couple of the goodies he is putting together that I'm interested in.

 

[EMSJEEP]

I want to ask this again. Are you running the vehicle off the diode?

Alternator - Breaker - Isolator - Battery 1 - PDC

The PDC is seeing the post isolator voltage.

This was a theory, and perhaps a bad one. I just don't see where a bad isolator would cause massive backfeed into the rear lighting. Additionally, these incidents have no corresponding post isolator voltage drop. While imprecise, I have known my dummy voltage indicator to be responsive and accurate.

 

[kastein]

Right now, no I won't, as I'm not a paying vendor and none of it is ready for prime time.

When I get everything lined up, I will, no problem... heck if you wanted to drive up here I'd probably help install it if you supplied the beer for the evening eace: I harbor no ill will for anyone unless they have willingly made my life difficult. Some well-meaning words on the internet in no way shape or form do that.

For the OP, I would suspect a bad ground or a lousy connection in a positive line... try running the engine and harassing the wiring harness in various places until the problem flares up, then focus on that area.

 

[EMSJEEP]

as an EE I would disagree with this.

tubes were more like a MOSFET than a diode - just one that happens to have a heater / light bulb built into it. Many specialized ones for power RF transmission and demodulation have more than one grid, up to 7 in the case of some heptagrid converter tubes.

Diodes do not work off resistance, they allow current to flow in only one direction and have a forward voltage directly related to the junction temperature, a physical constant (whose value depends on the material used to create the diode, germanium, silicon, gallium arsenide, indium gallium aluminum phosphide, etc), and forward current, see Shockley's Diode Equation for more details.

However that is neither here nor there, since the regulator in a 2001 is controlled by the PCM, which uses as feedback the voltage it sees on its power lines (which come after the diode isolator in his setup) the regulator will be cranking up the field voltage on the alternator a bit to compensate for the minor forward voltage drop of the diode isolator, so the battery SHOULD be receiving full charging voltage and whatever current it requires. The way it does it with the vehicle off as well makes me think this is entirely unrelated to the isolator and is probably a corroded terminal or loose connection somewhere.

EDIT: also - if I am understanding it correctly the purpose of the isolator in this case is to separate the two batteries but charge them both via the alternator, i.e. discharging one battery fully will not affect the other.

Yes, I have an accessory system, computer, lighting, radios, compressor etc etc on the secondary system.

This reads more and more like a bad ground somewhere, but I can;t track it down. The fact that it seems to be heat related (or use related) has me completely lost.

 

[kastein]

Computer as in a laptop or something, not the engine computer, right?

My bet since it flares up when you hit the lights is something in the positive wiring between the PDC and the fuse panel (i.e. on the line protected by the 50 or 60 amp maxifuse) or a ground in the lighting or power accessory harness that also affects the ECU or CCD bus. The power accessories and lights draw a significant amount of current when in use, if those have a flaky ground they can easily drive the rest of the system nuts given the right combination of bad connections. Since it is tough to figure out exactly where, I'd just hit em all. It can't hurt, can only help. Especially pay attention to the stud on the left inner fender near the ECU with the 3-4 ground connections from the engine/chassis wiring harness. My blinkers and some other stuff were going completely haywire on my 98, turns out (the vehicle was a "some assembly required" bargain from a friend of mine) they were completely disconnected and I had forgotten to reconnect them.

 

[EMSJEEP]

Computer as in a laptop or something, not the engine computer, right?

My bet since it flares up when you hit the lights is something in the positive wiring between the PDC and the fuse panel (i.e. on the line protected by the 50 or 60 amp maxifuse) or a ground in the lighting or power accessory harness that also affects the ECU or CCD bus. The power accessories and lights draw a significant amount of current when in use, if those have a flaky ground they can easily drive the rest of the system nuts given the right combination of bad connections. Since it is tough to figure out exactly where, I'd just hit em all. It can't hurt, can only help. Especially pay attention to the stud on the left inner fender near the ECU with the 3-4 ground connections from the engine/chassis wiring harness. My blinkers and some other stuff were going completely haywire on my 98, turns out (the vehicle was a "some assembly required" bargain from a friend of mine) they were completely disconnected and I had forgotten to reconnect them.

I did the main grounding straps first...actually replaced one I didn't like, and then those on the left fender when I got the transmission range sensor code along with the backfeed into the high beam light. I then directly grounded the isolator for good measure. I think I have the map of grounds somewhere, but my ability to work is limited by being at school.

 

[EMSJEEP]

Update:

Problem happens without the isolator installed; problem happens without the Alternator and fuse attached (ie. running the vehicle off the battery). No voltage drop on the idiot gauge. P0705 code. Dim lights, stalls under electrical load (lights, windows, brake lights, etc.) Along with the apparent grounding issue with the rear lights...mean anything to anyone about where the potential bad ground may be?

 

[EMSJEEP]

Here are instructions on how to install a 3 post isolator: http://www.newmarpower.com/pdf/Manual-Battery%20Isolators.pdf

If I read the FSM right, the alternator connects to the PDC Main Bus

So the lead from the alternator should have been moved to the ALT terminal of the ISO, and the BAT1 Term should then be connected to the PDC with something like #6 wire. Durring normal operation, you should have your full 13.8V as the monitoring of the battery voltage is done on the PDC side of the ISO.

The Second battery should be on the BAT2 side.

Is that what you did? If not, please supply drawing.

Ron

Alternator goes to battery; battery goes to PDC.

Theory as far as what has changed. Intermittant backfeed into the high beam circuit, dimly illuminating the dash light and dimming (significantly) the D/S low beam, was found to be due to a faulty headlight plug. Plug was replaced, high beam light is now CONSTANTLY dimly lit when lights are on, but lamp shines bright. Crossover in the H4 bulb?

 

[EMSJEEP]

Bad ground in the rear lighting harness, left side, point 1061. Problems resolved.