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Re: Alternator for Volvo MD2030

Thanks everyone, I really appreciate the help. I went to the boat today and snapped a pic to show you but it looks just like the ones posted. The yellow wire is clearly available externally. How does this work? The same screw with the yellow wire on it is connected to the battery + terminal so I presume this is where the power comes out. What does the voltage sense do?

Thanks again.
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Re: Alternator for Volvo MD2030

Also, if I wanted to replace this with an internally regulated, approximately 150A alternator, what would you folks suggest? MainSail mentioned something about the foot length, so here is a picture of that:
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Re: Alternator for Volvo MD2030

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Originally Posted by jarcher View Post
Thanks everyone, I really appreciate the help. I went to the boat today and snapped a pic to show you but it looks just like the ones posted. The yellow wire is clearly available externally. How does this work? The same screw with the yellow wire on it is connected to the battery + terminal so I presume this is where the power comes out. What does the voltage sense do?

Thanks again.
The voltage sense wire senses the voltage of the battery. In the Valeo alternator, it is assumed that the battery voltage on the positive terminal represents the real voltage of the battery. This is rarely true. You can simply unclip it from the alternator post and lead it straight to your battery for better accuracy.

Alternately (or in addition), you can put a diode in-line with it and use its voltage drop to trick the alternator into providing higher voltage and more current than it would normally while charging.

Mark
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Re: Alternator for Volvo MD2030

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The voltage sense wire senses the voltage of the battery. In the Valeo alternator, it is assumed that the battery voltage on the positive terminal represents the real voltage of the battery. This is rarely true. You can simply unclip it from the alternator post and lead it straight to your battery for better accuracy.

Alternately (or in addition), you can put a diode in-line with it and use its voltage drop to trick the alternator into providing higher voltage and more current than it would normally while charging.

Mark
Thanks Mark... Just to confirm, the yellow wire in this pic is the voltage sense wire, correct? The red wire you see is very short and leads to the lug on the starter motor where the cable from the battery connects, so that squares with what you said.
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Re: Alternator for Volvo MD2030

Yes, that yellow wire is the voltage sense wire.

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Re: Alternator for Volvo MD2030

Mark, thank you again.

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Yes, that yellow wire is the voltage sense wire.
With this alternator, if there is zero voltage on the sense wire will the internal regulator start?

Thanks very much.
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Re: Alternator for Volvo MD2030

I don't know, but I suspect one of two things will happen - it either will not put a field voltage on the alternator, or it will go full-field. If I was forced to pick, I'd guess no field.

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Re: Alternator for Volvo MD2030

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I don't know, but I suspect one of two things will happen - it either will not put a field voltage on the alternator, or it will go full-field. If I was forced to pick, I'd guess no field.
So if I was using a battery isolator, that would cause none of the battery voltage to appear at the input of the isolator, and therefore no voltage on the voltage sense wire as the alternator is currently set up.

If that is a problem could I just connect the alternator voltage sense wire to the the + terminal of one of the batteries? In fact, if I use a less expensive diode based isolator as opposed to an FET one, could I put the voltage sense on one of the batteries anyhow so that the regulator can make the correct voltage?

The downside I see to this is that the batteries will be in different states of charge but that would cause more current to flow through the less charged battery anyhow. I guess I would want to sense at the house battery in that case.

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Re: Alternator for Volvo MD2030

Most FET-based isolators have a circuit that puts a low-current battery voltage on the alternator input so that the alternator can see a voltage to start with. If you are buying one, make sure it has this feature and wire the circuit to your house bank.

If you use a diode isolator, wire the sense to the house bank output terminal.

If it were me, I'd just run the sense wire directly to the house bank itself, unless the wire run distance between the bank and the isolator is short with little voltage drop.

Curious as to why you are going with an isolator instead of a combiner. I have been assuming you are charging a main house bank and a small start battery. With a combiner, you would not be holding the start battery at a high voltage for a long time waiting for the house bank to fully charge.

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Re: Alternator for Volvo MD2030

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Originally Posted by colemj View Post
Most FET-based isolators have a circuit that puts a low-current battery voltage on the alternator input so that the alternator can see a voltage to start with. If you are buying one, make sure it has this feature and wire the circuit to your house bank.
Cool, I also see that some have the ability to detect the switch, so this can be optional. I'm looking at the Argo 180-3AC.

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Curious as to why you are going with an isolator instead of a combiner. I have been assuming you are charging a main house bank and a small start battery.
This is right. The house bank is LFP and the start is AGM.

Quote:
With a combiner, you would not be holding the start battery at a high voltage for a long time waiting for the house bank to fully charge.
Using a diode based isolator will allow me to run the alternator with a charge reference controller (I'm planning a VRC-200). I'll take the sense from the house LFP bank to the VRC-200. Then the VRC-200 will cause the alternator to give me voltage appropriate for the LFP bank. The AGM will usually remain mostly charged so the current it draws should be low and the diode will then drive its voltage a little higher.

A combiner or DC-DC charger has limited current passing ability and someday I expect I'll want to upgrade the alternator so I can charge the LFP bank more quickly. This design should still be valid with a higher current (like 150A) alternator.
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