Anyone have manual or wiring diagram for a Kestrel 90 alternator controller?

[Wafi]

New (to me) boat has a Kestrel 90 alternator controller. Searching the forum makes it fairly clear that I should consider replacing it if I want my new batteries to last. However the boat's wiring is a bit hard to trace, and documentation on the Kestrel 90 would help confirm that it's wired they way I think it is.

 

Other related questions:

• I've located the extra wire to the alternator brush. Is there more than one way that this could be configured within the alternator? I'm keen not to add dismantling the alternator to the "immediate" part of the jobs list unless absolutely necessary. If there is more than one possible configuration, is there an easy way to determine which I have with a volt/ohm meter?
• Is the Mastervolt Alpha Pro 3 a reasonable drop-in replacement (from a functional perspective)? Any alternatives to consider?

 

Other relevant info:

• Alternator is rated at 14V 70A (Cargo 110497).
• Batteries are 2 x ~200Ah banks (lead acid) plus a ~100Ah starter battery, charged via a Sterling Pro Split R
• Electricity usage is modest by modern standards - 800VA inverter powering a 240V fridge and the usual water pumps, LED lights etc. No electric kettles, microwaves, washing machines, saunas etc. 
• Engine is a Russell Newbery DM2 (so I probably couldn't upgrade to a more powerful alternator even if I wanted to)
• Boat will either be cruising or on shore power with float charging via Victron inverter charger (when the isolation transformer finally arrives and I've fitted it)
• Boat also has a diesel generator (which charges batteries via the Victron inverter charger)
• Planning to fit a Victron Cerbo GX to monitor power usage in due course
• May ultimately upgrade to Lithium batteries, but not for at least the next couple of years. Reluctant to spend megabucks purely to facilitate a future upgrade that may never happen, but would consider a more expensive option if it also looks after my lead acid batteries a bit better.
• I have an engineering/IT background, so happy reading circuit diagrams, modifying wiring, configuring devices etc, but would prefer not to create another large project that has to be completed before I can go boating.

[Tony Brooks]

31 minutes ago, Wafi said:

I've located the extra wire to the alternator brush. Is there more than one way that this could be configured within the alternator? I'm keen not to add dismantling the alternator to the "immediate" part of the jobs list unless absolutely necessary. If there is more than one possible configuration, is there an easy way to determine which I have with a volt/ohm meter?

 

Yes, but it depends upon which side of the rotor the regulator is, so on any A127 (that is what a Cargo 110497 is) the extra wire will be on the same side. What might also vary is how the new remote regulator connections are placed.

 

I think that the Mastervolt instruction sheet should give you the info you need. I am afraid that I can't remember 100% if the A127 has the regulator in the positive or negative side of the rotor, and without one to strip and have a look I cannot be sure

[Kingdom Isambard Brunel]

The alternator sensing wire connects to the brush that has a varying voltage on it when the revs are increased. The other brush will have only a static positive or negative voltage on it depending on the wiring.

The easiest and   sure  way is to check that this brush connected to the controller voltage is changing with revs using a multimeter.

From memory the Kestrel is a pretty poor alternator controller knocked up by Acorn Engineering in Denton Manchester, you could be better buying a new controller elsewhere, like Sterling.

Edited March 30, 2025 by Kingdom Isambard Brunel

[dmr]

But won't the voltage change regardless of whether its a P or N type alternator?

I thought that almost all British/European alternators where N, while America favours P?

 

In many cases the wire is soldered to an easily removable brush box so its not a huge job to find out what is going on.

[Kingdom Isambard Brunel]

1 hour ago, dmr said:

But won't the voltage change regardless of whether its a P or N type alternator?

I thought that almost all British/European alternators where N, while America favours P?

 

In many cases the wire is soldered to an easily removable brush box so its not a huge job to find out what is going on.

Yes, but only one brush will have a variable voltage, rev dependent, no matter what type the alternator is. 

[dmr]

10 minutes ago, Kingdom Isambard Brunel said:

Yes, but only one brush will have a variable voltage, rev dependent, no matter what type the alternator is. 

Yes but....the OP needs an easy way to find out if he has a P or N alternator before he gets a new controller, its 95% likely to be N but can't be sure. Ideally from a simple measurement on the wire coming out of the alternator, and Im not sure there is one.

 

On the subject of controllers, The Mastervolt looks good but is medium expensive, plus you need somebody to program it or spend more money on an interface. Also it does not measure current or alternator temperature itself but wants to be part of a Masterbus system. If the OP thinks he might go Lithium in the future then a Zeus or Wakespeed would be a better investment but there are both serious money.

[GUMPY]

Does one need an external regulator?

They were designed in the days when the output voltage of an alternator was 13.8v, now most alternator internal regulators are at 14.2v/14.4v  are external regulators needed?

[alan_fincher]

I'm reasonably (say 80%) certain that I may still have an old manual for a Kestrel controller.

Unfortunately though, if I do, it will be on the boats, where I currently am not.

I have no plans to be there for a week or two (I think), but when I do go, I'll have a look around.

 

For what it's worth I'm firmly of the view that if you have a Kestrel you should get rid of it ASAP.

[Kingdom Isambard Brunel]

22 minutes ago, alan_fincher said:

 

 

For what it's worth I'm firmly of the view that if you have a Kestrel you should get rid of it ASAP.

Ditto!

[Tony Brooks]

35 minutes ago, alan_fincher said:

For what it's worth I'm firmly of the view that if you have a Kestrel you should get rid of it ASAP.

 

Me as well. I understand it involved timing the length of the boosted voltage and gave the ability to start the timer all over again. Nowadays with twin alternator boats or single alternator ones with a properly wired split charge relay or VSR I doubt you need anything extra than a 14.4V regulator - unless there are undersized cable problems you are trying to hide.

[nicknorman]

In my experience - of which zero is with a kestrel reg - decent modern alternator controllers bring big advantages in lead acid charging. So whilst a standard 14.4v built in reg is OK, a good modern (digital) alternator controller is much better.

[Wafi]

Thanks all - lots of useful information.

 

Now less keen on the Mastervolt - by the time I've also bought the USB interface to manage the configuration it's close to half the price of a Zeus, which would integrate with the rest of my Victron system and be more future-proof. The Zeus handles P and N alternators (via a configuration option), so that's one less detail to worry about. The one complexity I haven't yet figured out is how well a Zeus will work with 3 separate battery banks (starter battery and 2 separate leisure banks). Not sure I'd have 2 separate leisure battery banks by choice, but that's not a change I want to make right now.

 

The other option is to get a Sterling regulator. That's almost a plug & play replacement for the Kestrel, and cheap enough that I won't mind replacing it if/when I upgrade to Lithium in a few years. Will a Sterling regulator be "good enough" for a mixture of flooded and AGM lead acid batteries, assuming I configure it for the (slightly lower) AGM charge voltage? I don't need to squeeze every last Ah out of the system, the priority is to avoid boiling/frying anything...

 

In the meantime, am I correct in thinking that unplugging the Kestrel's alternator field connection will be enough to stop it frying my batteries while I dither about what to replace it with?

[Kingdom Isambard Brunel]

Disconnecting the + live feed would be better.

The Sterling controller is a good product for you as you can alter the peak charge voltage and the float voltage to suit your batteries. It is cheap and reliable.  Tin hat on now to avoid all the flak from disgruntled purchasers. I have found them to be fine. 

[Wafi]

Quick update: I eventually went with a Wakespeed, partly thanks to @PeterF's excellent thread showing how well it integrates with a Victron system. It also plays nicely with the Sterling split charge device (Pro Split R) driving my separate battery banks, which didn't look straightforward with the Zeus. I don't necessarily need two separate leisure battery banks, but that's what's on the boat at the moment, and I don't want to have to change everything at once.

 

Installation was very straightforward - very nearly a drop-in replacement for the Kestrel, with a few additional connections for alternator temperature, taco and a shunt. Those additional connections were optional; I could have connected it directly to the four-way terminal block the Kestrel had been wired to, with just one additional power cable to the alternator, and it would have worked. I haven't tried any of the fancy configuration options yet, but with a fairly basic configuration (from memory, just battery and alternator details) it seems to work pretty well, and is hitting the right voltages at the right times; it's a doddle to see what it's doing on the phone app.

 

For anyone who finds this thread while searching for information on the Kestrel 90, I eventually found a wiring diagram on the Wayback Machine:

Thanks to everyone for the help and advice!