Peregrine

If this is so, that's a result!

No. I've checked through both the standard Isuzu manual and the additional one for canal boat users, and there's nothing.

It's an Isuzu 42, dating from 2007. The boat's manual said it would be a Lucas 70 amp alternator, but the alternator label didn't identify the manufacturer, and was marked "80 Amp". Googling its HMI (Isuzu) part number led to the Prestolite website page for the 66021126 alternator, which gave lots of detail, but not the number of poles. However, their Contact Us page has an email address for their European operation, so I sent off an ROI and got a reply first thing Monday morning!

Many thanks to all who responded. It resulted in: Getting a very speedy email response from Prestolite confirming that the alternator is 12-pole Downloading a strobe/tachometer app for my best beloved's rather old iPhone In the end it was a "Doh!" moment. As I was fiddling with the app, I realised that I'd not measured the crankshaft pulley correctly. That is 5'', and the alternator pulley is 3", so the correct calculation is 5/3 * 12/2 = 10 pulses per revolution. I'd entered 8 first time around. Once that was in, the idling speed was shown as 800 rpm, which is a little higher than that shown by the old tachometer, but perfectly reasonable. (Of course, though now OT, that means that the engine alternator is just starting to provide charging current at tickover, while the domestic alternator with a 6" pulley is spinning at 1600 rpm, which the spec chart indicates should yield about 15 amps. Not great, but a bit better than what I'd assumed under the old regime.)

Following the discussion I started last autumn about a new tachometer (http://canalworld.net/forums/index.php?/topic/87213-replacing-a-tachometer/#comment-1882715) I bought a VDO Viewline. The calculation to calibrate it for the pulses from the alternator is straightforward, but means knowing the number of poles that the alternator has. The part number label shows it's a Prestolite AS123 80 amp, though the Aqualine's manual says it's a Lucas 70 amp. I can't find any official info on the web about the number of poles, but one forum suggested that the Lucas A127 type typically has 12, so that's what I used in the calculation. However, that's producing a reading of about 1000 rpm at tickover, whereas the old tacho read about 600, and I don't know which one is correct. Without a strobe hand-held I'm a bit stuck! Please does anyone know how many poles the AS123 has, or where I could find that info?

That's useful, Tiggs. Thank you.

I recently posted a query about replacing a tachometer on a 9 year old Aqualine with an Isuzu 42 engine. Many thanks to those who responded, especially Tony Brooks. At the same time that the tachometer failed, the ignition warning buzzer malfunctioned, but while Oxley Marine were looking at these control panel problems, it seemed to recover, so I didn't mention it. Since then it has stopped working again at start, but sometimes sounds during the stop procedure, as it should. I would like to fix this – it feels like a dodgy connection, but obviously may be a faulty device. However, I can't find any mention of the buzzer in the manual. It's not on the very clear Isuzu wiring diagram. So I don't know whether it's a separate device, or whether it's part of one of the other instruments on the control panel. I would like to be clear what I'm looking for before I dismantle the control panel again. Does anyone know, please [a] where the buzzer is located; where it fits in the wiring scheme?

Thanks, markgregoryuk2000 and Tiggs. It's always hard to know [a] what you gain or lose by going for a cheaper option, and the value of a single negative comment – which I found for another cheaper make as well. Thanks, Tony. It sounds as though the current one is like yours. The guy at Furneaux Riddall indicated that the new one comes with a wiring loom, but there is also a wiring kit to convert from the old one to the new. There's nothing on their website about it, so I need to go back and ask him for more details. What I don't know is where the buttons are that you press to programme the thing – on the back of the meter or to be mounted elsewhere. The installation instruction PDF doesn't say. I saw a YouTube video for installing one in a car that had them mounted under the dash. I'm not afraid of the theory around alternator poles, etc – but I am worried about installing something in a control panel in a less-than-watertight way!

Erin Mae is an 9 year old Aqualine boat with an Isuzu 42 engine. The VDO tachometer has stopped working and Oxley Marine have declared it dead. I can live without a tachometer for the moment, but I would still like to replace it. Suppliers to my two favourite boat yards have a replacement, but for serious, silly money. I've found a VDO Viewline for less than half the price from Furneaux Riddell in Portsmouth, which looks as though it is a thoroughly updated version. However, the helpful bloke on the phone suggested it was quite complicated to fit. Any comments, please, on things to think about in fitting a new tachometer.

Final report – if anyone's interested. Bench testing of the alternator showed both rectifier and regulator to be faulty, so they've been replaced. Along the way I learnt considerably more about internal and external alternator wiring. Thanks to Tony and Nick for helping in my education.

Thanks again to both Tony and Nick. The alternator belt is fine. I seem to be getting charge into the battery bank, which is presumably coming from the engine alternator. We're currently on our way to Skipton, and a conversation with RCR has resulted in a decision to hurry that up and book in for Pennine Cruisers to have a look at the alternator. In case it's of interest, I'll report back once that's done.

Thanks Nick. Your comment, if I understand it, clarifies for me something from Tony's response. Do I take it that the warning light is normally connected between alternator D+ and the battery +ve, but with a diode on the circuit so that it only lights if the alternator voltage is lower than the battery voltage? I understand that might indicate an alternator problem. I should have thought about the belt slipping. I'll check that first thing in the morning. One reason for being puzzled is that I could see a reasonable charging voltage at the battery with the engine running, even though the warning light indicated a problem. But that might be the effect of having both alternators connected to the A2B, even though the engine alternator is (IMO) under-pulleyed.

Thanks, Tony. 1. I have a 330W solar panel, but I don't think that can be the issue. I noticed it shortly after setting out this a.m. when the batteries were relatively low, and I was in Garrow tunnel at the time! 2. I'm not sufficiently familiar with alternator circuitry to understand all you said about D+. I googled it and found some Prestolite stuff which helped and indicated it was a warning light terminal. But I'm not sure what you mean by "difference in voltage between the battery and alternator output to D+". 3. I don't understand your reference to "both warning lamps". It's just the one that is misbehaving. But it is true that the two alternators may be interacting, since they are both connected to the input terminals of the AB12160. They are identical alternators (standard Lucas type 70 or 80 amp) but they have different sized pulleys on the crankshaft, so potentially a different output. However, I understood that alternators cope happily with being connected in parallel.

Today in a tunnel I noticed the auxiliary light on my Isuzu engine control panel was lit, though inconsistently and not to its maximum brightness. The manual says the light is a warning that the domestic batteries are not charging. Erin Mae is an Aqualine with an Isuzu 42 and what they call the Deluxe Engine Control Panel. The Auxiliary warning light sits on the panel alongside the ignition switch and lights. I have the original circuit diagram for the boat, but the wiring for this warning light is not on the diagram, so I don't know what it is checking. Two years ago I installed a Stirling AB12160 alternator to battery charging device, which takes the output from both alternators and uses it to charge both the engine battery and the domestic set (and is supposed to do some other clever stuff). This means the output from the domestic alternator is routed via this gizmo, but I don't know whether or how this will have impacted the wiring to the warning light. Anyway, I have never seen this problem until now. I'm naturally anxious that this will create havoc on the domestic side of the electric. But I don't know what the problem is. Does anyone have any ideas before I call out the engineer?

The 204 is the 203 + True RMS. You decide whether that's needed on a boat. When I got my 204 it was going for the same price as a 203. Perfectly happy with the purchase.