A127 Alternator opening rpm’s mod?

[Blaster]

Hi all,

 

just got a new alternator to replace a dead one and out of the box I find out that the opening rpm’s for the regulator is 1384rpm.

 

the whole idea is to use it as a battery charger at idle at 800rpm so my question, will it work as it and will still produce something anyway or I need to replace the regulator (by which one? Any suggestions?) ? Thanks in advance 

[frangar]

Alternator RPM is rarely engine RPM. Measure the size of the engine pulley and the alternator pulley to work out the ratio and you will know what rpm the alternator is doing for what engine rpm. 

[Tony Brooks]

Remember that is the alternator speed, not the engine speed. The alternator will spin far faster than the engine they are normally fitted to.  I can't remember  the typical a pulley ration, but between 4 and 6:1 sounds plausible.

 

The regulator has nothing to do with the cut in speed, but a higher wattage warning lamp may help lower it.

[pearley]

That's the alternator speed, not engine rpm. At 800 revs engine speed the alternator will be spinning at around 3000 revs depending on the diameters of crankshaft pulley and alternator pulley.

 

Just for info if it's a modern engine like a Beta then battery charging at idle us not recommended.

[Alan de Enfield]

You should not charge your batteies via the alternator at 'idle'.

 

Start engine and check charging current, increase revs, the charge current will increase.

Increase revs until the charging cirrent doesnt increase.

 

Leave engine running at this speed until the charge current starts to fall, reduce revs until the cgarge current start to fall further

Keep running at these revs until the current starts to fall 

 

repeat repeat.

 

This way you get maximum charge for the fuel used and don't over heat the alternator by running it too slowly.

[Blaster]

14 minutes ago, pearley said:

Just for info if it's a modern engine like a Beta then battery charging at idle us not recommended.

Not, this is a Thornicroft 1.8 but what is the crack with the new engines anyway? Why charging at idle is not recommended? 
cheers

15 minutes ago, Alan de Enfield said:

You should not charge your batteies via the alternator at 'idle'.

 

Start engine and check charging current, increase revs, the charge current will increase.

Increase revs until the charging cirrent doesnt increase.

 

Leave engine running at this speed until the charge current starts to fall, reduce revs until the cgarge current start to fall further

Keep running at these revs until the current starts to fall 

 

repeat repeat.

 

This way you get maximum charge for the fuel used and don't over heat the alternator by running it too slowly.

That’s a very interesting advice I have never heard of. Will definitely try out.

So if let’s say I find a sweet spot at some 1100 rpm then I should keep the engine running at these for few hours? Would it not damage the engine? Cheers

Thanks for your replies, everyone, very helpful 👍🏻

[Tracy D'arth]

Running a diesel at tickover does more damage than running it at a speed where it develops more torque, vibrates less and gets proper lubrication for the bores rather than glazing them which leads to excessive smoking.

[IanD]

4 minutes ago, Tracy D'arth said:

Running a diesel at tickover does more damage than running it at a speed where it develops more torque, vibrates less and gets proper lubrication for the bores rather than glazing them which leads to excessive smoking.

There's also the risk of torsional resonance in the crankshaft/drive plate, which is why Beta say minimum speed for high-current charging is 1200rpm -- alternator load can be much heavier than prop load at low rpm.

[cuthound]

1 hour ago, IanD said:

There's also the risk of torsional resonance in the crankshaft/drive plate, which is why Beta say minimum speed for high-current charging is 1200rpm -- alternator load can be much heavier than prop load at low rpm.

 

Furthermore these are automotive alternators, designed to go under the bonnet of a car, which is open to cool air at the bottom. When installed in the engine hole of a boat cooling at low revs and high load is less effective as it is more reliant on the alternators fan. Running at revs higher than tickover allows the alternator fan to do more cooling. alternator fan 

[Alan de Enfield]

15 hours ago, Blaster said:

That’s a very interesting advice I have never heard of. Will definitely try out.

So if let’s say I find a sweet spot at some 1100 rpm then I should keep the engine running at these for few hours? Would it not damage the engine? Cheers

Thanks for your replies, everyone, very helpful

 

It is a well know fact, (and is normal practice for anyone who understands the management of electricity on their boat) not only to get the 'most bang for your buck,. but also for the reasons stated in the above posts.

[blackrose]

On 27/06/2023 at 17:28, Alan de Enfield said:

You should not charge your batteies via the alternator at 'idle'.

 

Start engine and check charging current, increase revs, the charge current will increase.

Increase revs until the charging cirrent doesnt increase.

 

Leave engine running at this speed until the charge current starts to fall, reduce revs until the cgarge current start to fall further

Keep running at these revs until the current starts to fall 

 

repeat repeat.

 

This way you get maximum charge for the fuel used and don't over heat the alternator by running it too slowly.

 

So what happens when boats are plodding down the canal at idling speed past miles of moored boats while the batteries aren't yet fully charged? Are the alternators overheating?

[Quattrodave]

44 minutes ago, blackrose said:

 

So what happens when boats are plodding down the canal at idling speed past miles of moored boats while the batteries aren't yet fully charged? Are the alternators overheating?

 

That's a good point; yes, but there's not.much you can do about the situation. But you are using diesel for propulsion and charging not just charging so the efficiency changes somewhat...

 

I've fitted a cold air feed to my alternator which seems to help although I've never taken any measurements.  A few years ago I saw an alternator that had a 5 or 6 turns of stainless pipe around it with water pumped through (boat was raw water cooled anyway) I rather liked that as a solution and  the pipe work was beautifully done...

Edited July 1, 2023 by Quattrodave

[nicknorman]

3 hours ago, blackrose said:

 

So what happens when boats are plodding down the canal at idling speed past miles of moored boats while the batteries aren't yet fully charged? Are the alternators overheating?

First of all, it isn’t a black and white thing. Not really “heating” or “overheating”. An alternator running very hot will have a shorter life than one that runs cooler, on a sliding scale. So it makes sense to avoid very long periods charging at idle, whilst short periods are unlikely to have significant impact. If you are the sort of boater who spends a long time in one place using the engine primarily for charging the batteries then most of the running could be at idle, charging. On the other hand if you mostly cruise daily and just occasionally run the engine tied up, it probably won’t matter too much.

 

But secondly, the nature of LA batteries is that after the first hour or so (depending on battery size vs alternator size) the charge current is likely to have reduced significantly and so the alternator won’t be working particularly hard.

Edited July 1, 2023 by nicknorman

[blackrose]

5 hours ago, Quattrodave said:

A few years ago I saw an alternator that had a 5 or 6 turns of stainless pipe around it with water pumped through (boat was raw water cooled anyway) I rather liked that as a solution and  the pipe work was beautifully done...

 

How would winding a pipe around a standard air cooled alternator possibly achieve any contact surface area between the two and produce any heat transfer?

[Tracy D'arth]

1 minute ago, blackrose said:

 

How would winding a pipe around a standard air cooled alternator possibly achieve any contact surface area between the two and produce any heat transfer?

Fairly minimally I would have thought, as you obviously think too.  Proper water cooled alternators are much more complex.

[Alan de Enfield]

5 minutes ago, Tracy D'arth said:

Fairly minimally I would have thought, as you obviously think too.  Proper water cooled alternators are much more complex.

 

I have a 170 amp water cooled alternator that has just had to be replaced - expensive! (£500) and required "half the engine" being removed & all the cooling system to be drained down and refilled

Edited July 1, 2023 by Alan de Enfield

[Quattrodave]

8 hours ago, blackrose said:

 

How would winding a pipe around a standard air cooled alternator possibly achieve any contact surface area between the two and produce any heat transfer?

 

Admittedly I didn't have chance to study it in detail but I believe it was welded to the casing.

[Tony Brooks]

8 hours ago, Quattrodave said:

 

Admittedly I didn't have chance to study it in detail but I believe it was welded to the casing.

 

That is interesting, stainless pipe welded to aluminium casting or welded to the laminated iron stator. I am musing about what welding the laminations would do. It might make it run even hotter because there may be less resistance to eddy currents in the joined laminations.

[Tonka]

Is overheating the alternator less of an issue when the engine is traditionally installed in an engine room?

[IanD]

1 minute ago, Tonka said:

Is overheating the alternator less of an issue when the engine is traditionally installed in an engine room?

Yes because it's usually a bit cooler than in an enclosed engine bay -- but what they *really* don't like is long periods of high-current charging into LFP batteries...

[Theo]

On 27/06/2023 at 17:28, Alan de Enfield said:

You should not charge your batteies via the alternator at 'idle'.

 

Start engine and check charging current, increase revs, the charge current will increase.

Increase revs until the charging cirrent doesnt increase.

 

Leave engine running at this speed until the charge current starts to fall, reduce revs until the cgarge current start to fall further

Keep running at these revs until the current starts to fall 

 

repeat repeat.

 

This way you get maximum charge for the fuel used and don't over heat the alternator by running it too slowly.

Exactly.

 

But I have a query:

 

As you run the alternaore more slowly the filed current supplied by the alternator regulator has to increase to keep up the output voltage of the alternator.  Presumeably this has a maximum value determined by the design of the system.  By reducing the revs and keeping the max output you are keeping the filed current at a maximum.  Why, then, will reducing the revs further mean that you overheat the alternator.  Won't heating reduce if the output reduces?

 

Nick

[nicknorman]

12 minutes ago, Theo said:

Exactly.

 

But I have a query:

 

As you run the alternaore more slowly the filed current supplied by the alternator regulator has to increase to keep up the output voltage of the alternator.  Presumeably this has a maximum value determined by the design of the system.  By reducing the revs and keeping the max output you are keeping the filed current at a maximum.  Why, then, will reducing the revs further mean that you overheat the alternator.  Won't heating reduce if the output reduces?

 

Nick

Maximum field current for your average alternator is about 4A so that means 60w power dissipated, which remains constant as the rpm decreases. But the fan is going slower so less cooling air. But there is less power being generated so less heat from the stator and main diodes. How that all balances out would be complex to work out. Too many variables.

 

But the other factor is the belt load.  For a given output power, the mechanical input power is roughly constant. The input power is belt speed x belt tension. So as you reduce the speed (rpm) the tension increases. So as you reduce the rpm until the output just starts to fall, belt tension peaks. Which is why I don’t subscribe to Alan’s tactic. IMO you should have the engine running somewhat faster, to reduce the belt tension - which is also of course a side force on the crankshaft pulley. Perhaps this isn’t a big deal for a small 70A alternator, but on large alternators it is.

Before we got our smart alternator controller, if there was a heavy load on eg 170A (charging low batteries or using the inverter) the engine was plainly not happy below about 1100rpm, the belt was prone to squeaking (despite being polyvee) and the engine laboured.

[IanD]

20 hours ago, nicknorman said:

Maximum field current for your average alternator is about 4A so that means 60w power dissipated, which remains constant as the rpm decreases. But the fan is going slower so less cooling air. But there is less power being generated so less heat from the stator and main diodes. How that all balances out would be complex to work out. Too many variables.

 

But the other factor is the belt load.  For a given output power, the mechanical input power is roughly constant. The input power is belt speed x belt tension. So as you reduce the speed (rpm) the tension increases. So as you reduce the rpm until the output just starts to fall, belt tension peaks. Which is why I don’t subscribe to Alan’s tactic. IMO you should have the engine running somewhat faster, to reduce the belt tension - which is also of course a side force on the crankshaft pulley. Perhaps this isn’t a big deal for a small 70A alternator, but on large alternators it is.

Before we got our smart alternator controller, if there was a heavy load on eg 170A (charging low batteries or using the inverter) the engine was plainly not happy below about 1100rpm, the belt was prone to squeaking (despite being polyvee) and the engine laboured.

Here's an example set of (large!) alternator curves to show what Nick said, you can see the increasing torque load on the engine as rpm drops. Also the cooling effect of the alternator fan drops rapidly as rpm falls (with rpm^2?) so the alternator gets hotter and hotter... 😞

 

[nb Innisfree]

Running an engine at tick over even when loaded takes much longer to reach normal operating temp esp in winter, at higher rpm more heat is generated and quicker warm up, once temp is reached it will hold it at lower rpm. I did a few runs at different speeds, at tick over in very cold winter temp, engine didn't reach temp after a couple of hours, whereas running at higher rpm it took about 1 hour. Best results were achieved by pre-heating with the Mikuni, took 10 mins or less.