Power (Electrical issues)

[Theo]

I think that you meant "Do get one " rather than "Do not get out one".

 

N

[Theo]

Some years ago I bought an ammeter. I got around to fitting it a few weeks ago. It has made a world of difference to battery charging. I have wired it up to measure only the alternator output.

 

It enables me to run the engine at the right speed to get maximum alternator output. From 60% I find that I am running the engine at 1200rpm for an hour or so. After that I can progressively reduce speed to tickover by the time the batteries have reached 75%.

 

I imagine that it is saving me no end of fuel.

 

N

[mango]

Some years ago I bought an ammeter. I got around to fitting it a few weeks ago. It has made a world of difference to battery charging. I have wired it up to measure only the alternator output.

 

It enables me to run the engine at the right speed to get maximum alternator output. From 60% I find that I am running the engine at 1200rpm for an hour or so. After that I can progressively reduce speed to tickover by the time the batteries have reached 75%.

 

I imagine that it is saving me no end of fuel.

 

N

Measuring the charging current with an ammeter is more satisfying, but it is easy to set the required engine speed using a voltmeter, preferably one that measures to 0.01V. Even a cheap multimeter will do the job. An ammeter is very useful for faultfinding, but a cheap DC clamp meter is adequate.

[Tony Brooks]

Measuring the charging current with an ammeter is more satisfying, but it is easy to set the required engine speed using a voltmeter, preferably one that measures to 0.01V. Even a cheap multimeter will do the job. An ammeter is very useful for faultfinding, but a cheap DC clamp meter is adequate.

 

I personally doubt that. A short while after the regulator starts to work and once the charging current has dropped a bit the regulators tend to maintain the voltage at a fixed level irrespective of speed.

 

To monitor the charging and battery both an ammeter and voltmeter are require but at different times in the charge-discharge cycle.

[Theo]

I used a voltmeter for ages and found it slow to respond. The ammeter gives instant rate of charging. What I am interested in is running the engine as slowly as possible for the maximum current.

 

N

[jollymoggy]

Not sure if I already said this but we only use a laptop and candles so the power should last longer. Anyway should be able to see the proof of the pudding tomorrow once the (split?) diode arrives. Anyway I did watch the mechanic while he checked the old alternator and I saw it was not enough voltage being given, he was going to replace the alternator with a 70amp but I asked for 100amp. It was a custom job for my engine with new pulley, bracket and belt.

Edited November 26, 2014 by jollymoggy

[bottle]

Just reading back through, your first post said you have 440 amp.hr of batteries and now you say you only have a laptop and candles.

 

In that case the batteries should last days before needing a charge but that charge would need to go on until the batteries were 'fully' charged

 

If you do only use the 240v ac for the laptop then it would make sense to get a 12v dc cable suitable for the laptop, that will save power.

 

Pity you have gone down the split charge diode line, it would have been better to go with a split charge relay

 

Basically diodes reduce the voltage to the batteries so reducing the charging voltage.

 

I think you may well be best advised to get the batteries charged fully via a shoreline or generator, if your batteries have not been charged properly they may be already knackered

 

Finally please be very careful with candles.

[jollymoggy]

Ok so I made a big mistake and connected my solar panels in series, to much voltage for my charge controller. Anyway I've redone it in parallel and all seems good now.

 

Also my new alternator is charging the batteries good now, So Shire Cruisers did a good job

[mango]

 

I personally doubt that. A short while after the regulator starts to work and once the charging current has dropped a bit the regulators tend to maintain the voltage at a fixed level irrespective of speed.

 

To monitor the charging and battery both an ammeter and voltmeter are require but at different times in the charge-discharge cycle.

I agree that an ammeter is useful but many boats don't have one fitted. I've checked about ten boats and in each case the battery voltage gave a good indication of what engine speed was needed to achieve maximum charge rate. If you push more current into a battery then the terminal voltage is bound to rise slightly because of the internal resistance.

[by'eck]

I agree that an ammeter is useful but many boats don't have one fitted. I've checked about ten boats and in each case the battery voltage gave a good indication of what engine speed was needed to achieve maximum charge rate. If you push more current into a battery then the terminal voltage is bound to rise slightly because of the internal resistance.

That last statement is true but only up to a point with alternator derived charging using its normal internal regulator.

 

As Tony said the battery charge voltage cannot and will not rise anymore once the state of charge has reached a point where the alternators voltage regulator comes into play, which I agree may need a certain mimimum revs. A voltmeter will give the indications you describe with batteries at lower states of charge and at low rpm for the simple reason the regulator is not limiting field current. Once the regulator cuts in its only a current indication which will reveal how much charge is going into the batteries.

[mango]

That last statement is true but only up to a point with alternator derived charging using its normal internal regulator.

 

As Tony said the battery charge voltage cannot and will not rise anymore once the state of charge has reached a point where the alternators voltage regulator comes into play, which I agree may need a certain mimimum revs. A voltmeter will give the indications you describe with batteries at lower states of charge and at low rpm for the simple reason the regulator is not limiting field current. Once the regulator cuts in its only a current indication which will reveal how much charge is going into the batteries.

I would always check charging current and battery terminal voltage to see how a system performs, and all I'm doing is to report what I have found so far.

[Alan Saunders]

That last statement is true but only up to a point with alternator derived charging using its normal internal regulator.

 

As Tony said the battery charge voltage cannot and will not rise anymore once the state of charge has reached a point where the alternators voltage regulator comes into play, which I agree may need a certain mimimum revs. A voltmeter will give the indications you describe with batteries at lower states of charge and at low rpm for the simple reason the regulator is not limiting field current. Once the regulator cuts in its only a current indication which will reveal how much charge is going into the batteries.

I may have misunderstood what you and Tony are saying; I agree with mango, maximising voltage at the battery or anywhere, even on a loaded circuit, is sufficient to optimise engine rpm for the best charge rate.

 

Despite complications due to rising battery voltage and surface charge the battery is effectively a resistive load, a higher voltage will result in a higher current.

 

Running the engine faster than the minimum required to keep the alternator regulator at its cut-off voltage cannot increase the charge rate.

 

I use a DVM with two decimal places, it matters little how accurate it is for this purpose. I plug it into a socket where I can see it from the throttle control. Two decimal places because the alternator (charger) voltage even at regulator cut-off of 14.4V or more is only one or two volts above the battery voltage.

 

Alan

[nicknorman]

I may have misunderstood what you and Tony are saying; I agree with mango, maximising voltage at the battery or anywhere, even on a loaded circuit, is sufficient to optimise engine rpm for the best charge rate.

 

Despite complications due to rising battery voltage and surface charge the battery is effectively a resistive load, a higher voltage will result in a higher current.

 

Running the engine faster than the minimum required to keep the alternator regulator at its cut-off voltage cannot increase the charge rate.

 

I use a DVM with two decimal places, it matters little how accurate it is for this purpose. I plug it into a socket where I can see it from the throttle control. Two decimal places because the alternator (charger) voltage even at regulator cut-off of 14.4V or more is only one or two volts above the battery voltage.

 

Alan

I think this is the point. Certainly the charge voltage and current are inextricably linked in the short term, however during much of the charge regime you get a large change in the latter for a small change in the former. This is why you need a DVM with 2 decimal places. That is fine, but many boats just have an analogue mechanical voltmeter, and it is pretty hard to detect the very small differences in voltage as the rpm is adjusted around the max output rpm. By contrast it is much easier to see the relatively large changes in current using a mechanical ammeter.

[Nightwatch]

I now have a duff alternator on our Barras shire. I have a couple of things I can do.

 

We are presently in Braunston, we can take the boat nearer to Dave Reynolds, some may know of him, he did a lot of electrical work for us in the summer.

 

Excuse the pun,not intended, we have an alternative, Ed at FC marine. He's along way from us but for £250 plus milage he will supply and fit a 90 amp replacement with all the shims and bolts and smaller pulley. Sounds a reasonable price.

 

Any ideas please. I know there are nearer fitter/engineers but I am not in contact with any of them.

 

Martyn

[Chalky]

If you can get to Coventry there is a place in Spon End (by the railway arches) that rebuilds alternators. Not used them for about 15 years however they did the alternator on my B GT for me. Google Maps puts the walking time from the canal basin at 20 minutes / 1 mile.

 

http://www.sacweb.co.uk/

[Nightwatch]

Thanks Chalky, to be honest we had the alternator rebuilt about four years ago, and since I have learnt that the standard alternator fitted to Barras engines are not as good as they could be. (Mondo or similar name) I feel that maybe they are not worth mucking about with continuously.

 

I have written to Ed at FC Marine to confirm cost but am open to suggestions still.

Martyn

Edited December 29, 2014 by Nightwatch

[Detling]

Ed fitted a 90 amp on our boat 20 months ago did a great job despite the snow. Still running and despite common statements earlier on the thread this 90 A alternator chucks out its amps when the engine is on 600 rpm (tickover) I have an ammeter on the alternator and the current does not increase as the revs do, so it is a decent low rpm alternator, Ed described it as being designed for marine use and not for use in a car.