Yanmar GM series tachometer sender assembly question

[vas]

hi all,

wondering how many sailboats running a GM series engine actually DO have a tachometer sender (as opposed to picking up tach data from the alternator, or maybe even not having a tacho at all seen that as well)
Trying to get decent RPM reading on a custom NMEA2000 box I'm building for my 2GMF running an 8kW generator and was smart (I thought at least!) enough to try devising RPM from the HZ of the 230V produced by the generator.
Works but gen is excited or anyway producing only signal over 2000 rpm so no way to know if engine is around idle or whatnot. OK, I do know since there's oil pressure registered, but it's a rough system and I'd like a bit more control if possible.
Since the generator doesn't have an alternator, I thought I'll get a dedicated yanmar tacho sender unit but don't seem to be able to find anything cheaply enough to justify the effort. At the 100+ mark I might as well get an alternator and be done with...

any ideas welcomed

cheers

V.

 

[vyv_cox]

There are many tacho sender units on Ebay from China, about £20 from memory.

 

[andsarkit]

I could have this wrong but if it is a basic generator it will be governed to run at 3000rpm to give 50Hz. If it has an inverter and the engine runs a variable speed then the inverter will also produce a constant 50 Hz so will not be related to the engine speed.
You could get a suitable magnetic pick up from Ebay but would have to make an adaptor to fit the threaded hole in the engine. A bit trial and error as you would need to know the number of teeth on the starter ring (assuming it picks up from there) or you could compare it with a reading from a handheld optical tacho.
Alternatively fit a small magnet in one or more of the holes in the crankshaft pulley and use the magnetic pickup in front of the engine.

 

[vas]

There are many tacho sender units on Ebay from China, about £20 from memory.

Vyv, seen a few but they seem rather generic and not sure if they'd fit, looks like there's a thread on the engine block in line with the flywheel teeth and it fits there.
No specs on that, I will remove they plug on mine tomorrow and try to find out what thread it is.
Wonder if some of them advertised for kubota and yanmar ym (?) series will do. Actually only seen this:
RPM Magnetic Pick up Sensor | eBay
and it's 50euro from the US.
Would ideally like something cheaper and I'm afraid as it stands now not from China, all parcels seem to be delayed due to coronavirus

I could have this wrong but if it is a basic generator it will be governed to run at 3000rpm to give 50Hz. If it has an inverter and the engine runs a variable speed then the inverter will also produce a constant 50 Hz so will not be related to the engine speed.
You could get a suitable magnetic pick up from Ebay but would have to make an adaptor to fit the threaded hole in the engine. A bit trial and error as you would need to know the number of teeth on the starter ring (assuming it picks up from there) or you could compare it with a reading from a handheld optical tacho.
Alternatively fit a small magnet in one or more of the holes in the crankshaft pulley and use the magnetic pickup in front of the engine.

basic generator, picking up from the mains output, multiplying the Hz*60 gives me RPM. Works but from 2000rpm onwards, dead under that, would like to find idle speed and generally where the governor sits as I'm playing with a linear actuator and slowly upping RPM when engine warm, and slowly dropping when I want to turn off. Being a 2pole thing runs at 3k constantly want to prolong it's life following a full rebuilt and improve my programming skills following a dead Mase control panel (doing my own touch screen to control the lot)

cheers

V.

 

[earlybird]

I made a tacho for my 2GM20 using an inductive pickup from Radiospares. The circuit was based on a PBO article using a frequency to voltage chip. Total cost was only a few pounds. It worked very well. The thread in the mounting hole is 24mm. dia. The pickup needs to be close to the ring-gear teeth, of the order of 1-2mm gap IIRC, so the mounting adapter needs to be accurate. I had the facilities to machine one from aluminium, but the plug from the engine might be useable with care.
Can't find the article just now, but I'm sure Google will come up with the type of circuit.

 

[vas]

thanks EB,

I've built a setup like that to measure another inductive load, my Bennett trimtabs, that was the most difficult h/w s/w problem I've tackled over the last couple of years that I'm playing the programmer in my free time
so any sender will do, just machine the threads right and hope to have space for a second nut to secure it at the right spacing from the teeth.
will see what I'll come up with

cheers

V.

 

[vas]

right,

after a light search, seems that the cheapest I can get designated for a yanmar/kubota is 50euro + customs from the US, else I can get this which produces digital output (so less work for me programming it ) for less than 10euro delivered to Greece from the UK. No brainer!
New 1Pc NJK-5002C Hall Effect Sensor Proximity Switch NPN 3-Wires Normally Open | eBay

OK, forgot to mention it's 12MM dia and not 24 but I can easily get an adaptor made from bronze or aluminium (whatever offcuts my machinist has)

cheers

V.