Engine - vintage engine altenator problem

[fin]

hi all. i need some help!!!! im running a john dorman 3lb engine in my barge. when we moved on the alternator didnt charge very well, so bit the bullet and bought a bosch 160 amp alternator and sterling digital regulator. when i fitted these i couldnt get the charge light to go out and only batt voltage.so had both alt and reg checked to make sure everything was ok, it was. i worked out that the alt wasnt spinning fast enough so i moved the 40 cm engine pulley to a faster pulley on the end of the engine and fitted a tiny pulley to the alt. after finding a belt big enough i fired her up.if i rev the hell out of her i can get the charge light to go out but the voltage drops to 12.8. i take it the alt/reg has kicked in but still not spinning fast enough to give full voltage and amps.is there a way round this because people run lots of these slow running engines.thanks for reading. cheers guys im on the track sort off .my problem with the fly wheel is that its all in encased didnt what to go cuttin holes. looks like its the only way forwards. thanks for all your replys

Edited July 13, 2008 by fin

[denboy]

bigger pulley on the flywheel would help

[bottle]

Hi Fin and welcome.

 

The experts will be along (it can be quiet at the weekend), the alternator will need to spin in the region of 2 to 5,000 rpm.

 

Check engine speed and measure the pulley ratio's, this will give the speed of the alternator.

[Ex- Member]

Yeah you'll need a good pully ratio as you have a slow revving engine. Even on our modern Perkins engine we have pullied up to around 5-1 Your alternator pulley will need to be at least 2" so to ensure a good grip from the drive belt, under 2" and the belt will most likely slip.

 

What is your engine revvs at idle?

What is your maximum revvs?

What's the diameter of the drive pulley?

And diameter of the Alt pulley.

 

Depending on the specific alternator, they generally require around 2000 rpm to begin charging at any decent rate. They're optimal rate is around 5000 to 6000 rpm.

Edited July 12, 2008 by Julynian

[David]

Hi

Our Kelvin runs the altenator OK but we have the belt round the 20" flywheel to the standard altenator pully approx 3.5", can just be seen on the red part of the flywheel, so a nearly six to one ratio, tickover 220 rpm max 1000 rpm normal running say about 600 rpm.

The altenator output when the engine first started can be less than maximum unless the engine is run at about 300/400rpm, BUT we don't sit with the engine ticking over so the output when underway is fine, after the batteries are well charged increasing the rev's from tickover has NO effect the volt and amp output stays the same at 220 as at 400/500 rpm. The altenator is running through an Adverc battery management also.

Edited July 12, 2008 by David

[Ex- Member]

Hi

Our Kelvin runs the altenator OK but we have the belt round the 20" flywheel to the standard altenator pully approx 3.5" so a nearly six to one, tickover 220 rpm max 1000 rpm normal running say about 600 rpm.

The altenator output when the engine first started can be less than maximum unless the engine is run at about 300/400rpm, BUT we don't sit with the engine ticking over so the output when underway is fine, after the batteries are well charged increasing the rev's from tickover has NO effect the volt and amp output stays the same at 220 as at 400/500 rpm. The altenator is running through an Adverc battery management also.

 

Stunning engine, nice work

[David]

Yeh but the cost of Brasso is crippling me

david

[Ex- Member]

Yeh but the cost of Brasso is crippling me

david

 

Worth every penny, and the elbow grease

[denboy]

Yeh but the cost of Brasso is crippling me

david

get some peek much better

[DHutch]

We have a 18" pulley down to a 3" to give again around 6to1.

- Crusing speed on the engine is around 120-150 on canals, upto about 250 on rivers, flat out 350 has been seen but rairly.

- However we have had our alternator modified to give improved charge at low revs, so it will work down to around 800rpm.

- Theres a few threads on the same topic inclusing one about the belting w used on ours whch had to be splitable to get the propshaft.

 

 

Daniel

[Arnot]

As a general guide, find out the maximum speed that the alternator can be run at and the maximum speed the engine can be run at. This will give you the ratio that the pulleys have to have to optimise the alternator performance.

 

Often the choice of engine pulley is limited but if it is too small, the appropriate alternator pulley works out to be unfeasibly small. Sometimes this can be resolved by the use of a polyvee drive belt system where a smaller alternator pulley can be used. A very small diameter pulley using a conventional drive belt has very little surface area to transmit the mechanical power and will tend to overheat and stretch on high loads, especially at moderate speeds.

 

It is also worth finding out the actual charge to shaft speed characteristic in graphical terms, some high power alternators don't start to deliver power until they are turning quite quickly and others with a slow rise curve need thrashed to actually achieve the quoted ouput.

 

Battery sensing does have an effect at moderate alternator speeds and tends to steepen the output curve giving noticeable gains at moderate speeds.

 

Having said all this though, I suspect that there may be another reason for your particular problems... Can you get it checked out by an expert (how I hate that word)?

 

Hope this helps,

 

Regards

 

Arnot

[Gibbo]

Battery sensing does have an effect at moderate alternator speeds and tends to steepen the output curve giving noticeable gains at moderate speeds.

 

You've said this (or similar things) a few times now.

 

If the alternator output voltage is below the regulation voltage then the field will have the full alternator output voltage across it and therefore maximum field current for that RPM. That is the output current limit for that alternator at that RPM into that battery state of charge.

 

How is battery sensing going to affect that?

 

It isn't.

 

Can you explain how you reach this conclusion?

 

Gibbo

[flatplane8]

Hi

Our Kelvin runs the altenator OK but we have the belt round the 20" flywheel to the standard altenator pully approx 3.5", can just be seen on the red part of the flywheel, so a nearly six to one ratio, tickover 220 rpm max 1000 rpm normal running say about 600 rpm.

The altenator output when the engine first started can be less than maximum unless the engine is run at about 300/400rpm, BUT we don't sit with the engine ticking over so the output when underway is fine, after the batteries are well charged increasing the rev's from tickover has NO effect the volt and amp output stays the same at 220 as at 400/500 rpm. The altenator is running through an Adverc battery management also.

 

Looks like a good setup, did you just use a belt around an unmodified flywheel? My JP3 is hand start only, but I may add an alternator at some stage, driven off the flywheel like this.

[MoominPapa]

Looks like a good setup, did you just use a belt around an unmodified flywheel? My JP3 is hand start only, but I may add an alternator at some stage, driven off the flywheel like this.

My FR2 has the alternator driven with a standard V belt running on the outside of the standard flywheel. It works fine, though I think the pulley ratio is a bit high: it overloads the engine a bit when it's running at lowish revs and the Adverc really winds up the output to charge well discharged batteries.

 

MP.

[David]

Looks like a good setup, did you just use a belt around an unmodified flywheel? My JP3 is hand start only, but I may add an alternator at some stage, driven off the flywheel like this.

 

Hi

Not a modified flywheel just around the bog standard rim which is about 2" wide, and ordinary belt of the type used on drilling machines etc I guess the lining up of the altenator is critical but it was on when we got it 5 years ago and never been touched not even needed tightening.

We are electric start but you can really notice the load the altenator puts on with a few seconds of firing up, really pulls the rev's down to about 80/90 rpm especially if batteries are down. More noticable if you compare it with a mates (a hand start job) rev's during warm up on petrol with no altenator fitted. But not bad enough to need a altenator switch off system. As you proberly know you cannot "rev up" when on the 30 or 40 seconds of petrol running with the kelvin, just with experience of each engine when to flip over to diesel.

david

Edited July 16, 2008 by David

[Chris Pink]

Looks like a good setup, did you just use a belt around an unmodified flywheel? My JP3 is hand start only, but I may add an alternator at some stage, driven off the flywheel like this.

 

You will need a switch on the alternator field coils as the effect of the load on hand starting is surprisingly large. As has been said there are no issues with running a v-belt off a 2" plus flywheel. If properly tensioned the belt won't move sideways as the alternator pulley V acts s a guide.

[flatplane8]

You will need a switch on the alternator field coils as the effect of the load on hand starting is surprisingly large. As has been said there are no issues with running a v-belt off a 2" plus flywheel. If properly tensioned the belt won't move sideways as the alternator pulley V acts s a guide.

 

Great, thanks for the info. Yes, if I do this I'll fit an 'off' switch as it takes a bit of spinning to get it to fire up. I'm still getting used to it.

[Arnot]

You've said this (or similar things) a few times now.

 

If the alternator output voltage is below the regulation voltage then the field will have the full alternator output voltage across it and therefore maximum field current for that RPM. That is the output current limit for that alternator at that RPM into that battery state of charge.

 

How is battery sensing going to affect that?

 

It isn't.

 

Can you explain how you reach this conclusion?

 

Gibbo

Essentially under the circumstances you outline, battery sensing will have no effect as you say.

 

However if at a given shaft speed and load impedance it is possible for the alternator output voltage to exceed the regulation voltage then a battery sensed system will allow the alternator output voltage to rise above the battery voltage to compensate for any losses in the distribution wiring and other components such as current shunts in the charging circuit. Since the output current is proportional to the difference between the peak voltage and the batteries nominal voltage and the peak voltage is higher, more current will flow.

 

The actual increase is a bit difficult to calculate in a theoretical sense due to the number of variables and essentially it would be futile in this application as the phenomenon can be readily measured.

 

The trouble is that this effect is quite difficult to explain in terms other than mathematical but if you have the opportunity try it! Get an alternator with a battery sensed regulation system and drive it into a flattish battery sufficient to clamp the voltage and measure the current as it rises to the point where the regulator begins to operate. Do this once with the sensing wire connected to the alternator output i.e. machine sensed and then again with the sensing wire connected to the battery positive i.e. battery sensed. You should observe an increase in the peak current of about 10%. and a more rapid decline in the charging current once regulation commences.

 

The practical effect of this in a situation where an alternator is charging a flattish domestic battery bank in a narrow boat is that because the alternator output voltage has to rise further before the regulator starts to reduce the rotor current, the maximum current is marginally increased but more importantly it is maintained at maximum level for longer. Even after the regulator starts to reduce the rotor current, it will reduce it less thus maintaining a higher charging current over the majority of the charging cycle. In a fairly well charged battery that has just been subject to a high load like a starting battery the replenishment cycle will be considerably shortened.

 

If you have such a system installed in a boat with some means of monitoring the charging current and are able to move the sensing point between the battery positive and the alternator output you will notice that when battery sensed, the high current is maintained for longer and once it starts to fall it does so more rapidly as a consequence of the more rapid early charge.

 

The benefit to the narrow boat owner is that the domestic battery bank can be charged more quickly and thus when moored without a shoreline available the engine does not have to be run for as long.

 

It’s probably worth pointing out that the effect I describe is not a theoretical hypothesis but an attempt at a simplified explanation of observations made over thirty-five years of building alternators and installing them in many applications that require an optimised charging regime.

 

I hope (but doubt) that this explanation will win you over so give it a go and see for yourself…

 

Kind Regards

 

Arnot

[Sir Nibble]

Gimme some information on the alternator, part number or perhaps a photo. Let's see if it's suitable for modification.

[Gibbo]

Essentially under the circumstances you outline, battery sensing will have no effect as you say.

 

I know. Thankyou.

 

However if at a given shaft speed and load impedance it is possible for the alternator output voltage to exceed the regulation voltage then..........................

 

But that's a completely different scenario.

 

We are discussing an alternator that isn't being driven fast enough.

 

You, for some reason, are now discussing an alternator that IS being driven fast enough and ways to overcome cable losses and increase alternator output voltage. Absolutley nothing to do with insufficiently revving alternators.

 

Gibbo

[Arnot]

But that's a completely different scenario.

 

We are discussing an alternator that isn't being driven fast enough.

 

You, for some reason, are now discussing an alternator that IS being driven fast enough and ways to overcome cable losses and increase alternator output voltage. Absolutley nothing to do with insufficiently revving alternators.

 

Gibbo

Chill man! I was only trying to share a bit of my experience and you are at liberty to take it or leave it. I didn’t really want to get into a convoluted discussion/argument, life is too short and I have an engine to play with. Why do you feel the need to jump down my throat? I bow to your superior knowledge of inverters and one of your posts taught me something interesting and useful about mains generator waveform - thank you!

 

More directly, I used the hypothetical case of an alternator rotating at a reasonable speed specifically to try to answer your specific question, not the original post.

 

However, as an observation on the original post, I would have thought that even a vintage engine with a 40cm pulley would have been able to turn an alternator at 5000 rpm or so at full engine speed and certainly would not expect the battery voltage to fall when the charge light goes out. I still suspect that it is not purely a problem of insufficient speed and that there is something wrong with this alternator, possibly a damaged stator and/or main rectifier. Anyway fin I hope you got it sorted out.

 

Regards

 

Arnot

[Gibbo]

Chill man! I was only trying to share a bit of my experience and you are at liberty to take it or leave it. I didn’t really want to get into a convoluted discussion/argument, life is too short and I have an engine to play with. Why do you feel the need to jump down my throat? I bow to your superior knowledge of inverters and one of your posts taught me something interesting and useful about mains generator waveform - thank you!

 

More directly, I used the hypothetical case of an alternator rotating at a reasonable speed specifically to try to answer your specific question, not the original post.

 

However, as an observation on the original post, I would have thought that even a vintage engine with a 40cm pulley would have been able to turn an alternator at 5000 rpm or so at full engine speed and certainly would not expect the battery voltage to fall when the charge light goes out. I still suspect that it is not purely a problem of insufficient speed and that there is something wrong with this alternator, possibly a damaged stator and/or main rectifier. Anyway fin I hope you got it sorted out.

 

Regards

 

Arnot

 

If I was any more chilled I'd be asleep.

 

Look at the subtitle of the thread..... "Altonator (sic) not spinning fast enough to charge"

 

Your post makes perfect sense. But only if the alternator is being spun fast enough! If it isn't, then an external controller (or battery sensing) will do p*ss all.

 

Gibbo

Edited July 17, 2008 by Gibbo