Battery Switches.

[john61ct]

Some alternators are not "AFD ready" without modification, similar to that needed for using an external VR

[coopec43]

Originally Posted by john61ct

Some alternators are not "AFD ready" without modification, similar to that needed for using an external VR

I have yet to read (and digest) all the posts/articles but my idea is that the alternator field winding is in two: the first part is connected to one AFD terminal and the second part is connected to the other AFD terminal.

When the switch is on "1/2/both" the two terminals are connected electronically and when the switch is "OFF" there is no connection so no field current and the alternator cannot charge.

Is that how it works?

Clive

[coopec43]

Why can't an air-conditioner pulley/clutch be used on an alternator in the absence of AFD? (The clutch would be actuated by the AFD terminals on the battery switch)


Clive

[Wotname]

^^ because it only takes milliseconds for the alternator diodes to blow when the output is disconnected. If the field is disconnected, the output is zero immediately. A clutch would leave the alternator spinning for say a second or more and therefore producing an output for long enough to kill the diodes.

[john61ct]

https://www.bluesea.com/resources/91

[coopec43]

Originally Posted by john61ct

https://www.bluesea.com/resources/91

Thanks John

I had come across that or something very similar before.

I think I'll handle it manually if the expert says the alternator has no AFD. I will be in sole charge of the ignition keys so no-one will be able to start the motor without the battery bank being "on". I will also insist the bilge blower be run for four minutes before starting the engine so the house bank will have to be switched "on".

Unless some idiot switches the isolator "off" while the motor is running I won't have a problem.

If somehow the diodes were destroyed it looks like I'd have to pull the alternator to bits to replace with spares? (I do notice you can buy after-market external rectifiers but I am not looking for work)


Clive

[coopec43]

I'm trying to work out if my alternator has AFD.

My alternator is similar to the aftermarket alternator pictured and is fitted to the same model vehicle.

Can someone tell me what IG, L and S stand for and is that relevant to AFD?

Clive

[john61ct]

AFD is not something an alternator has or doesn't have.

The questions are

1. is the alt designed to work with an external regulator?

or if not,

2. can an alternator shop modify its wiring

to work with my switch with the AFD feature?

which would be similar to what's required to get it to work with an external VR.

My understanding is the answer is Yes for most alternators, all you're doing is interrupting the field current circuit.

[coopec43]

Originally Posted by john61ct

AFD is not something an alternator has or doesn't have.

The questions are

1. is the alt designed to work with an external regulator?

or if not,

2. can an alternator shop modify its wiring

to work with my switch with the AFD feature?

which would be similar to what's required to get it to work with an external VR.

My understanding is the answer is Yes for most alternators.

I have been told my alternator has been wired for AFD. The alternator ran off the motor of a Toyota Coaster bus and the power output was used solely for the on roof air-conditioner. (Why wouldn't you put the Air Con compressor on the motor instead of an alternator? Maybe cheaper to put the alternator on the motor?)

I think AFD would make sense in a situation like that.

Yes I have read that AFD can only be used if the regulator is external.(I think it is just a bit harder if it is internal)

Gord May is a regular poster on this forum and he confirms what you are saying as he made a relevant post back in 2003. (I hope he won't get me for breach of copyright)

The Zap-Stop Diode connects between the alternator output and ground.
It is just a high voltage Zenner diode, with a reverse breakdown voltage (± 20 - 25VDC) a bit higher than the operating voltage of the alternator.
When the (transient) voltage exceeds this level, the diode starts to conduct, instantly shorting it to ground.

The alternator (rectifier) diodes are designed for high amperage, at relatively low voltages.
The Zap-Stop diode is designed for high voltages but will only handle high amperage for the few milliseconds it takes for the regulator to regain control.
I don't think it could stand up to something like a loose sense wire, on a high amperage alternator, where the voltage and current output stays high for any length of time.

A Battery Selector Switch with Alternator Field Disconnect (AFD), has an “extra” pair of (small) terminals, which open as the selector is rotated toward the OFF position. If connected in series with the Alternator Field wires, this auxiliary switch will interrupt the connection to the alternator’s field, preventing damaging transients.
Accordingly, the AFD auxiliary switch will only work when you have access to the Alternator Field Wires. This is the typical situation with Externally Regulated Alternators; but an Internally Regulated Alt’ can have the Field Wires brought out (<$50 at an Alt Shop).

Every multiple battery switch I have worked with has been a “Make-Before-Break” design, with the switching sequence “OFF”– “1”– “ALL”– “2”. This allows you to select between 1, 2,. &/or All (Both) without ever disconnecting the batteries.

I always use both an AFD-type Battery Selector Switch & a Zap-Stop Diode.
__________________
Gord May

[coopec43]

This is precisely what I want to do.

I don't want to charge batteries through the 1/2/Both/Off switch. I want use that switch for the distribution.

BUT I want to charge the batteries directly like Btrayfors suggests. Surely that is just so logical?

To get the full thread
http://www.cruisersforum.com/forums/...tor-66471.html


Yes, many boats are wired with the output of the alternator routed to the starter solenoid. From there, it depends. Many boats are wired, as I said before, with the starter wire going to the 1-2-ALL-OFF switch common lug (along with other house loads). This is because many boats use the selector switch to choose either house batteries or start battery, or to combine them.

IMHO, this is a very bad idea...for several reasons, not just the danger of blowing diodes if you switch to OFF. For example, with the start circuit effectively tied to the house loads thru the common lug, when you activate the starter you draw down the voltage considerably, possibly affecting onboard electronics. Worse, when you let up on the starter button and the starter stops, its magnetic field collapses and puts a very healthy voltage spike on the circuit...again, possibly damaging onboard electronics over time.

Even with a make-before-break selector switch...as many modern ones are...if you switch to the OFF position you have cut the path from the alternator output to both battery banks. Therein lies the problem...this can blow your alternator diodes very fast, unless the field current is somehow disabled simultaneously.

A MUCH BETTER solution is to wire the alternator's output directly to the house batteries, though an appropriate fuse located near the batteries. Then, use a voltage-follower device or a battery combiner to take care of maintaining the start battery.

Bill

[Wotname]

Originally Posted by coopec43

I'm trying to work out if my alternator has AFD.

My alternator is similar to the aftermarket alternator pictured and is fitted to the same model vehicle.

Can someone tell me what IG, L and S stand for and is that relevant to AFD?

Clive

IG = Ignition (switch)
L = Lamp (charge lamp)
S = Sense (for the regulator to sense the voltage to regulate correctly)

Not relevant to AFD

Unless your alternator has been modified so that different functions have been provided to these pins, you have an internally regulated alternator and therefore no access to disconnect the field externally i.e. no provision for AFD wiring.

[coopec43]

Originally Posted by Wotname

Unless your alternator has been modified so that different functions have been provided to these pins, you have an internally regulated alternator and therefore no access to disconnect the field externally i.e. no provision for AFD wiring.

Thanks for that. Yes I think I have been led up the garden path.

I am not really interested anymore as I intend to follow Btrayfors advice and charge the house batteries direct without going through the 1/2/both/off switch.

Do you have any problems with his post?

Clive

[john61ct]

Yes following best practices

wire alternator, all significant inputs, direct to House

charge Starter via automated combiner / ACR / VSR etc

and only use these bank switches to direct load feeds,

then no need to worry about AFD

[coopec43]

Originally Posted by john61ct

Yes following best practices

wire alternator, all significant inputs, direct to House

charge Starter via automated combiner / ACR / VSR etc

and only use these bank switches to direct load feeds,

then no need to worry about AFD

Thanks! That make it so simple.....


Clive

[daveNZ]

In wiring the alternator +ve direct to the house bank, and where the is -ve is through the engine, where on the alternator would I wire the negative, just under the head of one of the mounting bolts?
And is there any reason to make +ve and -ve the same length?
Thanks.