Split charge diodes on Yanmar alternator

[davidwf]

Fitted a second battery today along with a diode spliter to the output of the alternator.

However now alternator warning lamp fails tro light and alternator fails to work.
If I reconnect the alt output back to the battery (bypassing the diodes) Alternator springs back into life again. Plus warning light now lights on turning the key. I suspect I need to add another wireto the alternator to get it to energise.

Any one out there done this and if so where does it go?

 

[sailorman]

sounds like you are using the wrong terminals on the splitter

This is easy to wire & better than a Diode

 

[davidwf]

Nope not using wrong terminals on splitter, yes agree a VSR is one way to correct this but I don't really like them, I prefer the batteries to be isolated from each other.

 

[dratsea]

Yes, back to alternator (control unit is wired into output side of alternator) put in a diode, no volts = no output. But if you rev the engine there may be enough residual magnetism in core of alternator to fire it up (momentary short of diode will do the same)

John

 

[sailorman]

read the Cyrix spec they are seperated /forums/images/graemlins/wink.gif & work very well i have one

 

[VicS]

This is I think happening because you are now trying to feed the warning light circuit backwards through the diodes. You cant, so it does not light so the alternator is not getting its initial excitation current.

What i dont understand though is that you are getting a feed to operate the starter solenoid. Reference to a wiring diagram would explain hopefully.

You need to feed all you engine electrics from the engine starter battery (Via the isolator of course) it seems that your warning light is fed from the output connection from the alternator while the supply for the solenoid is fed from the battery.

I assume therefore you do not have everything operating via key operated switch like you have in a car for example.

Need a circuit diagram really to explain/investigate any further but I think what you will have to do is feed the warning light circuit from the same place as the starter solenoid circuit. May need a bit of rewiring to sort out as you wont want it on permanently.

Hope you can see what I am trying to get at. Thinking cap still on!

You have chosen a diode splitter for your own reasons, rightly or wrongly , but what are you doing to overcome the volts drop across the diodes?

I cannot follow Sailorman's reasoning about the Cyrix not connecting the batteries in parallel. Exactly what it does do as far as I can see (but maybe he's right and Ive missed something) but its great advantage is no volts drop and I suspect would not have caused the present problem.

 

[davidwf]

The Cyrix is a VSR and all it does is connect them in parallel ( Albeit in a sophisticated way using a micro processor to stop the relay cutting in and out when load is applied) when the primary reaches a set voltage, which is fine if that what you want. I don't, hence the use of a diode splitter. In terms of voltage loss the Victron is a shotky diode so loss is acceptable to me.

Looking at the circuit diagrams of alternator and of the engine it seems that the alternator is a voltage sensed one and I have found reference to fitting a relay to apply 12v to the battery terminal of the alternator from the starter swich position. This gets the alternator started. However easier method may be to buy a splitter from Barden or Drftgate that actually cater for voltage sensed alternators. Think I dropped off with the Victron.

 

[VicS]

Would like to look at the circuit diagram. What engine are we talking about. There may be a manual with a diagram on line.

Not sure what you mean by "voltage sensed" do you mean "battery sensed" or "machine sensed".
If its battery sensed you can connect the sensing wire to one of the batteries and then it will compensate for the volts drop on the splitter. You still get some volts drop even with Schottky diodes.

 

[davidwf]

Yes meant Battery sensed, have discovered that Victron Fet splitters have a battery sensed connection whereby you connect the switched live to it and it applies a voltage to the Alternator B+ terminal. This allows the alternator to energise.

So hopefully will be able to exchange the splitter tomorrow.

 

[halcyon]

[ QUOTE ]
In terms of voltage loss the Victron is a shotky diode so loss is acceptable to me.

[/ QUOTE ]

Have you measured the volt drop ?

Brian