Battery Isolator with Battery Drain

[DeepFrz]

It's called obfuscation, I believe.

[nnyerges]

Originally Posted by nnyerges

Ben (Bensigler),
I carefully read all the posts on this topic you have started. Nice debate on how a diode works.. but, I’m left with a doubt about the alternator sense terminal. Noted that most participants emphasis on where to connect the sense, as if there were only one alternator in your entire case. I read you have a twin engines and a 2ALT-IN x 3BATT-OUT ISOLATOR (terminals A1, A2 and B1, B2 & B3 I suppose), so I assume that each of your engine has its own alternator with its own sense terminal (not only one), so I do not understand why all they where talking about. You have two sense terminal i guess, so I would like to verify with you if the sense of each alternator, are connected to the Isolator output side B1 and B3, or failing that, more effective, on each of the batteries connected to terminals B1 and B3. Is that correct?

When i ask this to Ben, en mi post #70, I was thinking in writing "absurd discussion about diode theory" instead than "Nice debate on how a diode works". But I can’t hold it anymore. Nigel the diode characteristics diagram uploaded by "donradcliffe" in his post #23, it’s very clear. You can invent a new type of diode with your theories if you wish, but can’t change the actual diode diagram. You are not trying to convince all electronic engineers in here, you are trying to convince yourself that you are not wrong. You can create a new topic about and take another beer, but let’s leave the diode in peace.

Instead, give a help and have a look to http://www.cruisersforum.com/forums/...nes-71472.html and lets see what you have in mind for that.

Chears,
Nicolas

[cal40john]

I believe what he's been trying to say goes like this. Do a 2 pane mesh analysis of the circuit. One pane has the charging source and one of the batteries. The other pane consists of the 2 batteries. (One of the batteries shares a leg of both meshes.) If you assume both diodes forward biased you can replace them with shorts for a first order analysis. For mesh analysis you pick a current direction for each pane and write the equations for the voltage drops around each mesh. If you only look at the current that you've assigned for the mesh that contains both batteries, you see current flowing into one of the batteries and out the other. This makes it look like one battery is supplying current to the other and that current is flowing backwards through one of the diodes. You calculate this current as part of the solution. The battery that shares the 2 panes has the 2 mesh currents flowing in opposite directions, so when you're done adding everything up the currents are all going the proper forward direction through the diodes, both batteries are being charged, and one at a higher rate than the other.


I think this is very confusing for most people and misleading if you don't truly understand that you are only talking about the current in a partial incomplete solution.

Mesh analysis method:
Mesh analysis - Wikipedia, the free encyclopedia

Originally Posted by nnyerges

When i ask this to Ben, en mi post #70, I was thinking in writing "absurd discussion about diode theory" instead than "Nice debate on how a diode works". But I can’t hold it anymore. Nigel the diode characteristics diagram uploaded by "donradcliffe" in his post #23, it’s very clear. You can invent a new type of diode with your theories if you wish, but can’t change the actual diode diagram. You are not trying to convince all electronic engineers in here, you are trying to convince yourself that you are not wrong. You can create a new topic about and take another beer, but let’s leave the diode in peace.

Instead, give a help and have a look to http://www.cruisersforum.com/forums/...nes-71472.html and lets see what you have in mind for that.

Chears,
Nicolas

[nnyerges]

Originally Posted by cal40john

both batteries are being charged, and one at a higher rate than the other.

Thats it, thats all, thats the obvius! Each battery its going to demmand what it needs from each diode, but not consumming the energy from each other trhu the isolator, just from alternators. Any way, Ben solve his problem. Lets move one and solve others issues.

Chears
Nick

[Andina Marie]

Originally Posted by nigelmercier

Of course, as I said above.
No I haven't. What I said was that the diodes caused "some current from the higher voltage battery to flow back round the loop to the other battery: subtracting itself from the incoming current to the higher voltage battery, and adding to the current to the lower."

This negative current is only a vector, it could not of course be measured as travelling in the oposite direction. Perhaps sailing terms would help. There is a tidal flow of 2 knots coming from the direction you are going in. Your speed through the water is 5 knots. The result is 3 knots COG. From inside the boat, you could not measure the tidal flow, it is a vector. But it is still there.

No, even considering a numerical vector, current won't flow from battery to battery.

If I'm correct in assuming you are talking about an alternator feeding 2 batteries through the typical diode isolator, you CANNOT make a case for current flowing back from a higher voltage back to the lower one. For current to flow backward through the diode on the battery with the higher voltage that diode would have to be CONDUCTING. It is only conducting if the alternator is at least 0.7 volts HIGHER than the higher voltage battery. If that is the case current must be flowing INTO the higher battery, not OUT OF it.

What happens in fact is the lower battery will take ALL the current put out by the alternator and drag the alternator voltage lower than the higher battery so no current can flow into (or out of) the higher battery.

You may like to say that the lower battery is "stealing" current from the alternator that would otherwise have gone to the higher battery but the current is still coming from the alternator, never from the higher battery.

[nigelmercier]

Originally Posted by cal40john

If you assume both diodes forward biased you can replace them with shorts for a first order [mesh] analysis...

In a nutshell, but nobody believed me

[goboatingnow]

Originally Posted by Andina Marie

No, even considering a numerical vector, current won't flow from battery to battery.

If I'm correct in assuming you are talking about an alternator feeding 2 batteries through the typical diode isolator, you CANNOT make a case for current flowing back from a higher voltage back to the lower one. For current to flow backward through the diode on the battery with the higher voltage that diode would have to be CONDUCTING. It is only conducting if the alternator is at least 0.7 volts HIGHER than the higher voltage battery. If that is the case current must be flowing INTO the higher battery, not OUT OF it.

What happens in fact is the lower battery will take ALL the current put out by the alternator and drag the alternator voltage lower than the higher battery so no current can flow into (or out of) the higher battery.

You may like to say that the lower battery is "stealing" current from the alternator that would otherwise have gone to the higher battery but the current is still coming from the alternator, never from the higher battery.

That was never said , in a circuit analysis however, in effect you analyse each branch with its sources and sinks and then vector add then together. The net result must obviously be consistent with observed activity but the analysis does have current flowing In all directions.

So in this case there are three sources. Each of these sources affects the branch currents. But the overall observed current is as you observed. What is true is that the more charged battery is affecting the net current flow into the more discharged battery.

Remember all sources in a circuit affect the circuit. Equally not all electrical analysis can be done by simple explanations. It is a science after all.


It's all basic kirchoffs law
Dave

[Andina Marie]

Sure, OK Dave.

However if you have diodes that you can make conduct in reverse you should replace them, irrespective of esoteric explanations.

[goboatingnow]

Originally Posted by Andina Marie

Sure, OK Dave.

However if you have diodes that you can make conduct in reverse you should replace them, irrespective of esoteric explanations.

Well I suppose we can all do "tongue in cheek". I presume you understand circuit analysis

Dave