Jump Starting My Engine

[chris w]

Well that's what I thought after reading Gibbo's post. But how many amphours can they supply? The battery is only about the size of a fag packet. It just doesn't seem to add up to me, but I suppose they work.

Starting an engine will usually take less than ONE Ampere-Hour.

 

Chris

[PaddingtonBear]

If that be the case, and I have no reason to doubt it nor to start WW3, why do all the shiny semi-trads and the like have two alternators fitted? Surely a single good alternator would put back the electrickery used in a trice and then could concentrate on replacing all that used by the five flat screen tellies usually found on such vessels.

Edited December 3, 2008 by PaddingtonBear

[MoominPapa]

If that be the case, and I have no reason to doubt it nor to start WW3, why do all the shiny semi-trads and the like have two alternators fitted? Surely a single good alternator would put back the electrickery used in a trice and then could concentrate on replacing all that used by the five flat screen tellies usually found on such vessels.

Nail. Head.

 

If the wiring can be organised so that both alternators can charge the house batteries, I suppose there's a possibility that two little alternators might be cheaper than one big one. I suspect that they're mainly there because most users/installers can't work out anything more complicated then "connect alt-1 to batt-1, connect alt-2 to batt-2"

 

 

MP.

 

Edited to add: It's also possible that mounting/driving two little alternators is easier than one big one, when using a van engine.

Edited December 3, 2008 by MoominPapa

[chris w]

If that be the case, and I have no reason to doubt it nor to start WW3, why do all the shiny semi-trads and the like have two alternators fitted? Surely a single good alternator would put back the electrickery used in a trice and then could concentrate on replacing all that used by the five flat screen tellies usually found on such vessels.

Most boats only have a single alternator and, in conjunction with a diode-splitter or relay, do an admirable job of charging both banks.

 

With 2 alternators, the wiring is simple, to which MP alluded, and there is also the possibility of combining their output to charge the domestics much faster. My new boat came with 2 x 80A alternators, one on each bank. The start battery alternator is sleeping after the first few minutes.

 

Many engines will have 2 alternators in case someone wants to add bow thruster batteries to the start battery alternator.

 

Chris

[FORTUNATA]

You can measure how many volts the alternator is giving out by use of a multimeter connected to the B+ alternator terminal and the negative alternator terminal and then the actual output at the battery terminals. Many basic alternators are fixed at 14 volts but some of the smart alternators will vary charge current from bulk to float charge and so on.

I've heard of cases where the actual voltage read across the batteries is significantly below alternator output mainly because on board appliances utilise some of the available current.

Back to the original poster, I suspect maybe he just has a slightly knackered starter battery for some reason.

 

If that be the case, and I have no reason to doubt it nor to start WW3, why do all the shiny semi-trads and the like have two alternators fitted? Surely a single good alternator would put back the electrickery used in a trice and then could concentrate on replacing all that used by the five flat screen tellies usually found on such vessels.

[Malarky]

Something worth checking is the connection of the positive feed wire to the starter motor, as I have known that to work loose, and avoid detection by not being easy to see.

[chris w]

I've heard of cases where the actual voltage read across the batteries is significantly below alternator output........

 

I'd like to see one of those!!!! The alternator and the battery will always be at the same voltage because they are connected directly together

 

The only time you will see a difference will be a fraction of a volt for cable volts drop OR if the alternator is connected to a split charge diode unit. If the latter, you MUST use battery sensing to take account of the maybe 2v drop across the diodes or else your batteries will not charge properly.

 

Chris

Edited December 4, 2008 by chris w

[FORTUNATA]

A 30 amp alternator was tested with a voltage of the standard 14 volts. Vessel load was 24 amps. The multimeter reading read 6 amps flowing into the battery terminal while the said terminal voltage registered 13.2 volts. Not really enough to get the job done.

Battery sensing is indeed the better option. The regulator senses voltage directly at battery terminals and would work fine with a simple relay system.

 

I'd like to see one of those!!!! The alternator and the battery will always be at the same voltage because they are connected directly together

 

The only time you will see a difference will be a fraction of a volt for cable volts drop OR if the alternator is connected to a split charge diode unit AND you are not using battery sensing. Since not using battery sensing is WRONG, with a diode splitter, the alternator voltage will always be the same as the battery voltage.

 

Chris

 

 

That's quite true. Bad connections in the wrong place create resistance, especially a poorly soldered connection to a starter motor wire. Likewise, the B+ feed wire from alternator to battery positive could use a visual check.

On my own boat I was surprised to find a bare section of alternator wire (thick guage) and it hadn't been insulated. It's not really such a big deal but a very simple matter for me to insulate it when I get round to it shortly.

 

Something worth checking is the connection of the positive feed wire to the starter motor, as I have known that to work loose, and avoid detection by not being easy to see.

Edited December 3, 2008 by FORTUNATA

[chris w]

A 30 amp alternator was tested with a voltage of the standard 14 volts. Vessel load was 24 amps. The multimeter reading read 6 amps flowing into the battery terminal while the said terminal voltage registered 13.2 amps. Not really enough to get the job done.

Battery sensing is indeed the better option. The regulator senses voltage directly at battery terminals and would work fine with a simple relay system.

You're getting confused, or the author of the book from which you keep quoting is confused...........

 

The alternator's regulator will LIMIT the highest voltage out to the battery to around 14.2v. HOWEVER, if the battery is discharged, ITS terminal voltage will be low, maybe only 12v. So the alternator's output voltage, when connected to a battery, is the BATTERY'S TERMINAL VOLTAGE. As the terminal voltage rises, so will the voltage measured at the output of the alternator because they are the same thing - they're connected together!!!

 

The alternator's current input to the battery will continue to raise the battery's terminal voltage higher and higher as the battery charges. At around 14.2v the alternator's regulator switches in and limits the voltage rise to protect the battery from damage.

 

So, in summary, if an alternator is supposed to give out 14v, that does NOT mean that it always gives out 14v but only as the battery gets to about 75% charge will it reach this figure.

 

It's just Ohm's Law. The alternator can be considered to be a generator with a series resistance (the stator windings). The current produced has to flow through the stator windings, which will therefore drop a small voltage, through 2 diodes in the rectifier, that's another 1.2v lost and into the battery.

 

As an example, at idle, when my batteries are down to 12.2v (50% discharged) I get about 27A charge current. At higher revs, I get about 52A.

 

So, I can calculate exactly the internal voltage that the alternator is producing. The stator windings present an impedance of about 0.1 ohms (delta wound) so 27A through those will drop 2.7v plus 1.2v for the diodes and it also has to overcome the 12.2v of the battery itself.

 

So, from Ohm's law, the internal voltage being generated inside the alternator is 2.7 + 1.2 + 12.2 = 16.1v This is the PEAK voltage generated inside the alternator (remember it's an AC voltage waveform out of the stator windings) and it's the peak voltage that appears at the output of the alternator (due to rectification), so the RMS voltage generated inside the alternator will be 16.6/√2 = 11.4v rms

 

You can measure this internal voltage by putting an AC voltmeter between the "W" (tacho) terminal of the alternator and ground, and indeed mine reads almost exactly 11.4v rms at idle when delivering this current.

 

At higher revs, the internal voltage will rise (due to the rotor's spinning faster) and the same calculation for 52A reveals the internal voltage will be 13.2v rms.

 

Note that, maybe surprisingly to some people, the rms voltage increased by less than 2v rms (about a 16% increase) but the current to the batteries virtually doubled.

 

With no load on the alternator, its open circuit voltage will rise to around 120v, so don't disconnect the alternator's output cable while it's running, or you will almost certainly fry the rectifier diodes.

 

Chris

[Iain_S]

I'd like to see one of those!!!! The alternator and the battery will always be at the same voltage because they are connected directly together

 

The only time you will see a difference will be a fraction of a volt for cable volts drop OR if the alternator is connected to a split charge diode unit AND you are not using battery sensing. Since not using battery sensing is WRONG, with a diode splitter, the alternator voltage will always be the same as the battery voltage.

 

Chris

 

Surely there will still be a voltage drop across the diode splitter, whether or not battery sensing is used. This will lead o the alternator voltage being higher than the battery voltage. (It does on my boat, anway )

Iain

[chris w]

Surely there will still be a voltage drop across the diode splitter, whether or not battery sensing is used. This will lead o the alternator voltage being higher than the battery voltage. (It does on my boat, anway )

Iain

You're quite correct, my fingers were typing quicker than my brain!!! Of course there will be a voltage drop across the diode splitter, that's WHY one must use battery sensing!!!!!!!!

 

The whole idea of battery sensing is that the alternator gets voltage feedback directly from the battery so that the alternator's regulator adjusts itself to take account of the drop across the diodes. The drop will be anything from about 1.2v up to maybe a full 2v.

 

So, a "normal" 14.2v alternator will increase its output voltage to say 16.2v so that after the drop across the diodes, the batteries still see 14.2v

 

I'll edit the post above.

 

Chris

[FORTUNATA]

The readings are taken to illustrate the effects of load on an alternator battery charging system. The more load you have, the less effective is the charge. Therefore, turning off as much load as possible will improve battery charge. A logical deduction as Mr Spock would say.

Taking voltage readings across alternator terminals is a pretty commonplace test and, as you said, it's normally done to test for voltage drop between alternator and battery terminals. Pehaps if cables are excessively long or, again as you stated, diode isolators are being used, there is a drop.

Yes, I know alternator current is three phase A.C. , converted to D.C. via the rectifier which is a bridge of six diodes that rectify A.C.. There is also the D+ alternator output which is also rectified via three diodes. Usually the B+ terminal is the one you can test.

At any rate, the point of the test in question isn't complex. If you're running lots of load at the same time as the battery bank is being charged, charging will be less efficient. That's why many boats improve on this by having a seperate engine destined purely for charging via another alternator while the main engine is relegated to propulsion.

However, I still think the O.P. may well just need a new starter battery or just test the one he has and see if it will charge fully.

 

You're getting confused, or the author of the book from which you keep quoting is confused...........

 

The alternator's regulator will LIMIT the highest voltage out to the battery to around 14.2v. HOWEVER, if the battery is discharged, ITS terminal voltage will be low, maybe only 12v. So the alternator's output voltage, when connected to a battery, is the BATTERY'S TERMINAL VOLTAGE. As the terminal voltage rises, so will the voltage measured at the output of the alternator because they are the same thing - they're connected together!!!

 

The alternator's current input to the battery will continue to raise the battery's terminal voltage higher and higher as the battery charges. At around 14.2v the alternator's regulator switches in and limits the voltage rise to protect the battery from damage.

 

So, in summary, if an alternator is supposed to give out 14v, that does NOT mean that it always gives out 14v but only as the battery gets to about 75% charge will it reach this figure.

 

It's just Ohm's Law. The alternator can be considered to be a generator with a series resistance (the stator windings). The current produced has to flow through the stator windings, which will therefore drop a small voltage, through 2 diodes in the rectifier, that's another 1.2v lost and into the battery.

 

As an example, at idle, when my batteries are down to 12.2v (50% discharged) I get about 27A charge current. At higher revs, I get about 52A.

 

So, I can calculate exactly the internal voltage that the alternator is producing. The stator windings present an impedance of about 0.1 ohms (delta wound) so 27A through those will drop 2.7v plus 1.2v for the diodes and it also has to overcome the 12.2v of the battery itself.

 

So, from Ohm's law, the internal voltage being generated inside the alternator is 2.7 + 1.2 + 12.2 = 16.1v This is the PEAK voltage generated inside the alternator (remember it's an AC voltage waveform out of the stator windings) and it's the peak voltage that appears at the output of the alternator (due to rectification), so the RMS voltage generated inside the alternator will be 16.6/√2 = 11.4v rms

 

You can measure this internal voltage by putting an AC voltmeter between the "W" (tacho) terminal of the alternator and ground, and indeed mine reads almost exactly 11.4v rms at idle when delivering this current.

 

At higher revs, the internal voltage will rise (due to the rotor's spinning faster) and the same calculation for 52A reveals the internal voltage will be 13.2v rms.

 

Note that, maybe surprisingly to some people, the rms voltage increased by less than 2v rms (about a 16% increase) but the current to the batteries virtually doubled.

 

With no load on the alternator, its open circuit voltage will rise to around 120v, so don't disconnect the alternator's output cable while it's running, or you will almost certainly fry the rectifier diodes.

 

Chris

[FORTUNATA]

Although we're straying from the original matter of the jump starter, this matter of charging has been mentioned in Canal Boat mag somewhere by one of the technicians. The disadvantage of the propulsion engine alternator is often batteries only get 70 per cent charge. If load is operating on the electrical system, charging current decreases. One of the technicians even suggested periodic charging via a charging device in order to get beyond just a 70 per cent charge.

[OptedOut]

Some interesting figures for a CAV CA45 starter motor.

Locked torque, Running and Light running.

 

[alan_fincher]

Some interesting figures for a CAV CA45 starter motor.

Locked torque, Running and Light running.

 

Blimey, I knew they can draw a lot, but that's scary.

 

Our boat is wired so the full starter current passes through one of those big black selector switches, which also doubles as the isolator for both sets of batteries. It's quite impressive that the switch will handle these currents without apparently suffering ill effects. I don't believe they are rated at anything more than about 100A.

[Sir Nibble]

Blimey, I knew they can draw a lot, but that's scary.

 

Our boat is wired so the full starter current passes through one of those big black selector switches, which also doubles as the isolator for both sets of batteries. It's quite impressive that the switch will handle these currents without apparently suffering ill effects. I don't believe they are rated at anything more than about 100A.

Don't panic, that's a fairly big starter, big enough to take a hold of most narrowboat engines and heave it over the side. Mosr little boat starters will draw about a third of that current.

[alan_fincher]

Don't panic, that's a fairly big starter, big enough to take a hold of most narrowboat engines and heave it over the side. Most little boat starters will draw about a third of that current.

Ah! - I wrongly saw the "45" in the number and assumed it might be similar to mine, which also has a "45" in the number, if I recall correctly.

 

I suspect I'm still taking liberties with the "big switch", but it came wired up that way, and until it misbehaves, I have better things to do than change the arrangement. I did think it might be playing up a month or two back, but it proved to be the connector not fully seated on the battery - the switch was fine.

[John Orentas]

Don't panic, that's a fairly big starter, big enough to take a hold of most narrowboat engines and heave it over the side. Mosr little boat starters will draw about a third of that current.

 

 

And of course that 4 figure current was "Locked Torque" presumably mechanically fully restrained.. There was a similar thread last winter I think, I made a point of testing my engine, on a very cold morning and cold engine.. I could not get a higher reading that 150 amps.

 

Needless to say I was told that I didn't know what I was talking about.. The "experts" who had probably never done the test were glibly talking about 300 amps for a smaller engine.

[chris w]

Blimey, I knew they can draw a lot, but that's scary.

 

Our boat is wired so the full starter current passes through one of those big black selector switches, which also doubles as the isolator for both sets of batteries. It's quite impressive that the switch will handle these currents without apparently suffering ill effects. I don't believe they are rated at anything more than about 100A.

If the switch is indeed rated at only 100A, then the emphasis will be on the word apparently

 

Chris

 

And of course that 4 figure current was "Locked Torque" presumably mechanically fully restrained.. There was a similar thread last winter I think, I made a point of testing my engine, on a very cold morning and cold engine.. I could not get a higher reading that 150 amps.

 

Needless to say I was told that I didn't know what I was talking about.. The "experts" who had probably never done the test were glibly talking about 300 amps for a smaller engine.

I haven't measured mine (Isuzu 35) on a cold day but on the warm, summer's day on which I tested it, the starter motor drew 140 amps.

[chris w]

Yes, I know alternator current is three phase A.C. , converted to D.C. via the rectifier which is a bridge of six diodes that rectify A.C..

 

There is also the D+ alternator output which is also rectified via three diodes.

 

Actually the D+ output is also rectified by 6 diodes. It has to be to get full-wave rectification. Three of the diodes are the so-called "field diodes" and the other three are the negatively bonded diodes of the main output diode bridge.

 

 

If you're running lots of load at the same time as the battery bank is being charged, charging will be less efficient.

 

You mean charging will be less effective. Charging efficiency won't change.

 

 

That's why many boats improve on this by having a seperate engine destined purely for charging via another alternator while the main engine is relegated to propulsion.

At least that makes the diesel split question a lot easier

 

Chris

[Sir Nibble]

Ah! - I wrongly saw the "45" in the number and assumed it might be similar to mine, which also has a "45" in the number, if I recall correctly.

The 45 in CA45 refers to 4.5 inch diameter, (Co-Axial 4.5).

The 45 on yours is probably a Lucas M45, where 45 still refers to 4.5 inch, it's not such a powerful unit tho' and will probably draw a lot less current.

 

Needless to say I was told that I didn't know what I was talking about.. The "experts" who had probably never done the test were glibly talking about 300 amps for a smaller engine.

 

I've tested thousands. I may well be wrong but as I recall you tested that to answer the hoots of derision when you suggested 50A as a likely figure. If you test again with the started locked you should indeed see about 300A and it is that peak current which can break down a poor connection with an audible crack when the starter is initially engaged. You are always fond of saying (rightly in my opinion) sod the theory, take a measurement and be sure. Like I said, tested thousands, literally thousands.

[John Orentas]

I've tested thousands. I may well be wrong but as I recall you tested that to answer the hoots of derision when you suggested 50A as a likely figure. If you test again with the started locked you should indeed see about 300A and it is that peak current which can break down a poor connection with an audible crack when the starter is initially engaged. You are always fond of saying (rightly in my opinion) sod the theory, take a measurement and be sure. Like I said, tested thousands, literally thousands.

 

 

You are turning into 'one of them'. If I remember 300 amps was one of the more conservative 'guesses'.. I never say anything without knowledge of the theory or practise, I was the only one who 'did the work' and tested my system on a very cold morning.. So you've tested thousands, on a bench in a warm workshop, 'brilliant' what does that tell you.

 

I know you are in the habit of aping your chums more idiotic assertions and you assume me to be some sort of ignorant oaf because I don't constantly blow my own trumpet as is the fashion around here.

[Tim Doran]

Wooooo a run away thread, back to my original post.

 

Last nights starter battery voltage was 12.7V read from my multimeter. I realise that it might be slightly off but I have compared it to the guage on my MasterVolt Controller panel and the readings were the same

 

I got home and clipped the jump starter on to the engine and tried to start her up. Very slow turning over but it did start eventually. Maybe I did not have a good connection. I forgot to mention that it is a barrus shire 35hp engine.

 

I got to dundas last night and filled up with water and slopped out . Before i finished for the night i tried restarting and it was fine. I ran the mikuni first thing this morning to warm the boat & engine. I do not normally do this becuase my fire is normally too warm, but I thought it might help. I started the engine this morning and it was fin started up really quick. It seems fine.

 

What do the experts think?

 

Thanks for all the help so far.

 

Tim

[chris w]

I never say anything without knowledge of the theory or practise...................

 

: You've posted in the wrong section. You should have put that in the "Friday Joke" bit.

 

I can't stop laughing, it's soooo funny

[Timleech]

Don't panic, that's a fairly big starter, big enough to take a hold of most narrowboat engines and heave it over the side. Mosr little boat starters will draw about a third of that current.

 

I've just bought an engine with a BS6, what can that potentially (or even Amperically <groan>) draw? :lol:

 

Tim