Alternators....

[Dave Payne]

Trying to understand things a little more and my next topic is alternator and what mine does, can't get to it at the minute to check the type I have but hopefully someone can explain how it works a little to me, I know it charges the batteries but at what level, also I recall reading at higher revs it only supply's maximum do a am certain period?

 

If I wanted to upgrade, add another, what is the best way to go about it in terms of choosing type and placement on my nanni engine?

 

Thanks

[WotEver]

Gee... this could be a book.

 

Q What level does it charge?

A. When operating correctly it will fully charge your batteries.

 

Q. At what revs?

A. It depends on the engine/alternator setup and the state of charge of the batteries. Batteries with a low SoC might need the engine to be revved up to say 1500 rpm to get the alternator to output its maximum. As the batteries become more charged the revs can be dropped accordingly towards tickover because the alternator no longer needs to spin as fast to achieve the required output.

 

Q. What would I upgrade to and how?

A. Let's firstly know what alternator you have (make, size), what size battery bank you have (type, size), what your power audit is, how long you generally cruise for daily, whether you have access to a shore line, whether or not you have solar.

 

Tony

[nicknorman]

Trying to understand things a little more and my next topic is alternator and what mine does, can't get to it at the minute to check the type I have but hopefully someone can explain how it works a little to me, I know it charges the batteries but at what level, also I recall reading at higher revs it only supply's maximum do a am certain period?

 

If I wanted to upgrade, add another, what is the best way to go about it in terms of choosing type and placement on my nanni engine?

 

Thanks

 

How it works: When you move a wire through a magnetic field, a current is induced. The reverse also applies - when you hold a wire in a changing magnetic field, a current is induced.

 

Alternators are normally the latter ie there is a fixed set of windings (stator) into which current is induced by means of a rotating magnetic field. The magnetic field is produced by some windings on the rotating bit (rotor) that are fed with current via slip rings. The amount of current produced depends on the rpm of the rotor which of course depends on the engine rpm and the ratio of the engine and alternator pulley diameters, and also depends on the strength of the magnetic field which in turn is determined by the rotor current, also known as the field current.

 

So to produce a certain output current you need the right combination of rpm and magnetic field strength. If the rpm is lower you need more magnetic field strength ie more field current to get the same output. But there is a limit to this - magnetism in a rotor's iron core has a limited maximum value. Increasing the current beyond this point doesn't increase the magnetic field. Thus there is a minimum rpm at which the alternator's maximum output can be produced. If the desired current output is lower then of course this can be provided at a lower rpm.

 

Of course the current output from the stator windings in the rotating magnetic field is AC. Rectifier diodes are built in to the alternator to convert this to DC (rippling DC, to be precise).

 

Typically a battery or boat's services will determine how much current they will take. If more current is supplied than they can take, the voltage rises. If less current is supplied than they can take, the voltage falls. So there is a regulator circuit within the alternator that tries to maintain an optimum voltage, say 14.4v. The regulator controls the field current in response to any difference between the actual voltage and the desired voltage. If the voltage starts to rise, the regulator reduces the field current and if the voltage starts to fall, the regulator increases the field current. In fact it controls the field current by switching the system voltage on and off rapidly, varying the ratio of on time to off time. The inductive property (propensity to resist changes of current) of the rotor/field winding means that in fact the current just rises and falls (ripples) a bit, it doesn't stop and start.

 

The power for the regulator and field current typically (although there are variations) comes from the alternator's own generated current. There are small field diodes within the alternator that rectify some of the alternator's output and this is used to operate the regulator and provide the field current.

 

Of course before the alternator starts to run, there is no output and so the alternator typically needs to be fed with current from the engine battery in order to generate the magnetic field. This is normally via the ignition warning light. The modest current flowing through the warning light is directed to the field winding and provides just enough magnetism to start the process off - at which point the alternator starts producing current that is used to operate the field windings. The voltage on the warning light's alternator connection then rises to system voltage and the light goes out. So if the bulb is blown, the alternator may never start to charge or only at very high rpm (as a result of residual magnetic field in the rotor).

 

Note that there are some variations in the detail about how the regulation works, how the alternator starts to produce current and so when fault finding, it is important to know what type of alternator it is.

 

In terms of upgrading the alternator, the limiting factor is normally the ability to drive it. A conventional belt has limited ability to transfer power and of course the actual load on the belt increases at lower rpm for a given amount of power (power being force x speed). So for a 12v system, conventional belt the limit might be 90A or so, although it will depend on the amount of "belt wrap", pulley size and engine rpm. For more power one really needs a polyvee belt that has much greater contact area than a conventional belt, is stronger and thus able to transfer much more force. For that of course you need polyvee pulleys on the engine and alternator.

Edited December 14, 2016 by nicknorman

[Tony Brooks]

The first thing to grasp is that it is the BATTERIES that "control" how much charging current they will accept EXCEPT if they will accept/want more current than the alternator can give it will or a time be the alternator that is controlling the current.

 

Now please read the above again to be sure you grasp it.

 

It is the alternator's design rather than any control systems that define the maximum current they can supply.

 

With well discharged batteries let us say they will accept 100 amps but you only have a 70 amp alternator. For a while the alternator will supply its 70 amps or close to. As the batteries charge they will accept less current so when they want 70 amps that is all that will flow, up to that time however much they will accept the alternator will only supply 70 amps. Throughout this time the charging voltage will be less that the alternator's data sheet says.

 

As the batteries charge they will accept less than 70 amps so the charging current gradually drops as the batteries charge while at the same time the design of the alternator causes the charging voltage to rise.

 

I have illuminated mains light bulbs from Lucas ACR alternators as a demonstration so left to do their own thing you could get well over 100 volts from an alternator but this will destroy your batteries so the alternator is fitted with a voltage regulator to prevent battery damage. On a modern alternator this will be set to between 14.2 and 14.5 Volts but it can vary while higher or lower set regulators may be available.

 

From the point the regulator starts working the charging current will be wholly dependant on what the batteries will accept PROVIDING the alternator is spinning fast enough OR other loads are not drawing current from the alternator and thus trying to make it exceed its maximum output.

 

In summary - at first its the alternator that "controls" the maximum charging current and after an unknown period of time it is the batteries that "control" the charging current.

 

That is how it works. I do not think that you need to go into how the current is actually generated or how the voltage is regulated.

 

 

Now to try and help with the upgrade.

 

Unless you have an unusually large battery bank or an unusually small alternator (hence some of Tony's questions) it is likely that the batteries will be limiting the charging current within an hour or so of start up and running at reasonable revs. Fitting a larger alternator will shorten this period of charging but we are probably, in most cases. only talking about by fractions of an hour and even if you invest to speed up this period of charging you will be left with MANY hours of charging to get the batteries all but fully charged - say about another seven give or take.

 

Once the regulator starts regulating the voltage the charging current will keep dropping so for much of those seven hours less than 20 amps will be flowing and this will gradually reduce to a much lower figure. This is where Solar comes into its own. After the initial alternator charging has been done for (say) three hours or so you can turn the engine off and for much of the year leave the solar to complete the charge for free. In the winter this is unlikely to work all the time so maybe charge for four hours per day at more than tickover and once a week charge for 8 hours.

 

Before spending too much money on charging I would suggest that you invest in a decent ammeter and voltmeter so you can monitor what is going on Be wary of any meter that claims to how percentage of charge with your present level of knowledge, all apart from the Smartguage are likely to tell you lies and ruin your batteries. Even the Smartguage has inaccuracies but it is head and shoulders more accurate than the others in the hands of ordinary boaters.

 

An ammeter will tell you when the batteries are more or less fully charged.

 

A Smartguage or a voltmeter plus experience/knowledge will tell you when to start charging.

 

I doubt a larger alternator will make a cost effective difference to charging times unless your boat is very unusual.

 

Note that I have not mentioned RPM. That is because as long a sits high enough it has little effect on charging current or voltage.

 

 

Nick and myself typing at the same time.

Edited December 14, 2016 by Tony Brooks

[nicknorman]

I'll just mention that having a big alternator isn't just about charging the batteries quicker. It is also about the ability to run a big load such as a washing machine, electric kettle from an inverter, without depleting the batteries.

 

It is certainly true that a big alternator doesn't substantially reduce the time it takes to fully charge a battery. However it does substantially reduce the time it takes to put some charge into the batteries, eg to go from 50% to 80%. So it can be good for an interim charge.

[Tony Brooks]

Agreed, but until the OP gives more details about his boat and his electrical use we can not help much more. Both our posts complement each other.

[OldGoat]

I'm quite a fan of the Adverc (and others) battery management devices because-

• they can keep the alternator charging for longer
• they have an element of battery conditioning built in (that you would get from a multistage mains charger)

I'm also keen on a 'commercial' style alternator as they are designed to run for long periods at high output. IMO they are better value than car types in the long run.

Both these are often available on eBay from time to time - if you're patient...

[BruceinSanity]

Agreed, but until the OP gives more details about his boat and his electrical use we can not help much more. Both our posts complement each other.

And compliments to the two of you for taking so much time and trouble!

 

I thought I knew quite a bit about this stuff, but Nick's post in particular helped straighten out my ideas.

 

Thanks, guys.

[Dave Payne]

Good posts,thanks.

 

Just had fun trying to bend myself everyway possible to find a label on the alternator, nothing, can only find some stuff on the plastic bit at the back which led me to discover it's he regulator, pr7736 made for the vale alternator which comes in three models,

 

A13N234

A13N259

A13N285

 

But no idea which one really

[reg]

Nick and Tony ty, double greenies

[Dave Payne]

 

Q. What would I upgrade to and how?

A. Let's firstly know what alternator you have (make, size), what size battery bank you have (type, size), what your power audit is, how long you generally cruise for daily, whether you have access to a shore line, whether or not you have solar.

 

Tony

Battery bank is 3 x 110ah open top batteries.

Power audit, no idea, never really done one, I run water pumps, led lights, 240v fridge off the invertor in standby mode.

Only really cruise once a fortnight maybe once a week for around five hours but run the engine for about three or four hours a day.

No access to hook up

Solar is 250watt panel.through mppt.

[Tony Brooks]

OK, so very similar to me except my panel is about 60 watts through a PWM regulator and I have a 12V fridge. Although I would prefer some battery monitoring instruments so I could see when front. That is providing you do all running for charging at a few hundred RPM above tickover AND you increase the once a week charge time to at least 8 hours OR accept suboptimal battery life.

 

I doubt anyone can say much more without voltage and current readings at various points throughout each 24 hours.

[bizzard]

A huge gas ring encircling the boat all alight and powerful with huge leaping flames will cause mist, fog and clouds to disperse locally above the boat allowing the suns wonderful rays to get through to play upon your solar panels.

Years ago this device but much huger were used to encircle the landing area at airports to disperse fog long enough for aeroplanes to land. Another method was to encircle the landing area with 40 gallon drums, burning petrol soaked rags. And to help pilots flare out and touch down the planes had a long stick ''called a Fog stick'' attached underneath the fusalage, hinged at the front with a caster wheel on the trailing end. The pilot would lower the trailing end of the stick with a string when on final approach. As the caster wheel touched the ground the Fog stick which was connected to the control column and engine throttles would automatically pull the control column back and close the throttles for flare out and touch down, without any input from the pilot who couldn't see the ground anyway.

I'm sure I saw one of these Fog sticks dangling from beneath an Airbus A340 the other day comin in to land in the fog at Stansted. The caster wheel looked decidedly Wilco or Pound shop.

[Dave Payne]

A huge gas ring encircling the boat all alight and powerful with huge leaping flames will cause mist, fog and clouds to disperse locally above the boat allowing the suns wonderful rays to get through to play upon your solar panels.

Years ago this device but much huger were used to encircle the landing area at airports to disperse fog long enough for aeroplanes to land. Another method was to encircle the landing area with 40 gallon drums, burning petrol soaked rags. And to help pilots flare out and touch down the planes had a long stick ''called a Fog stick'' attached underneath the fusalage, hinged at the front with a caster wheel on the trailing end. The pilot would lower the trailing end of the stick with a string when on final approach. As the caster wheel touched the ground the Fog stick which was connected to the control column and engine throttles would automatically pull the control column back and close the throttles for flare out and touch down, without any input from the pilot who couldn't see the ground anyway.

I'm sure I saw one of these Fog sticks dangling from beneath an Airbus A340 the other day comin in to land in the fog at Stansted. The caster wheel looked decidedly Wilco or Pound shop.

 

I want what you are drinking!

[Dave Payne]

 

OK, so very similar to me except my panel is about 60 watts through a PWM regulator and I have a 12V fridge. Although I would prefer some battery monitoring instruments so I could see when front. That is providing you do all running for charging at a few hundred RPM above tickover AND you increase the once a week charge time to at least 8 hours OR accept suboptimal battery life.

 

I doubt anyone can say much more without voltage and current readings at various points throughout each 24 hours.

 

 

 

Only just started running at over tickover the last couple of weeks, thought for some reason running above was bad for the engine.

 

I do have to admit that i fitted the new batteries, el cheapo from ebay, back in june, before i had the solar fitted, i think i may have done damage early on, to be fair though i went for the el cheapo route so i could understand how to kill a set of batteries, crazy i know but at £150 its not a big deal.

 

Going forward i do need to fit some better things to see exactly what is going on with my batteries through the day and when charging.

 

Looking at what i think is my alternator online, i can see i either have the 60 amp or 70 amp, so if we say 60 amp to be safe, i usually see my batteries touching 50% in the morning (using a cheap voltmeter wired into the circuit) thats with lights pumps and fridge running for the last 12 hours, if i run my engine for hours then i should be seing the batteries rise to at least 90%, is this fair to say?

[bizzard]

 

I want what you are drinking!

It was all occurring before ww2 at aerodromes. The trouble with the huge gas ring of leaping flames was that when the gas was turned on for fog dispersal the gas works couldn't cope with the sudden demand and complaints came flooding in from residents for miles around that their gas stoves had gone out right in the middle of cooking dinner.

Another problem was the security of the caster wheel on the Fog stick, as one happened to fall off a plane and strike an elderly lady on the napper concussing her, whilst on its approach to Croydon airport, the main airport for London before London airport at Heathrow came about.

Edited December 14, 2016 by bizzard

[ditchcrawler]

A chap I worked with worked for the National Grid or what ever it was called in the 60. He said the most important documents in the control room was the Radio and TV times. The load increase due to the end of TV programs when kettles went on made a big difference when one of the soaps was showing a cliff hanger.

[WotEver]

... i usually see my batteries touching 50% in the morning <snip> if i run my engine for hours then i should be seing the batteries rise to at least 90%, is this fair to say?

Maybe. 80% is likely, 90% maybe. The only easy way to tell is with an ammeter.

 

As for the 50%, you need either an accurate Voltmeter or (better) a SmartGauge. An inaccurate Voltmeter is neither use nor ornament.

[BruceinSanity]

A chap I worked with worked for the National Grid or what ever it was called in the 60. He said the most important documents in the control room was the Radio and TV times. The load increase due to the end of TV programs when kettles went on made a big difference when one of the soaps was showing a cliff hanger.

This getting well off topic, but I saw a piece just the other day saying that the guys in the NG control room have to have Strictly on so as to predict when folk will drift away from the telly and turn the kettle on.

[David Mack]

This getting well off topic, but I saw a piece just the other day saying that the guys in the NG control room have to have Strictly on so as to predict when folk will drift away from the telly and turn the kettle on.

Surely much less of a problem these days when everyone is watching a multitude of channels and catch-up TV, compared with the time when everyone was watching Morecambe and Wise or whatever on BBC1 at the same time.

[ditchcrawler]

This getting well off topic, but I saw a piece just the other day saying that the guys in the NG control room have to have Strictly on so as to predict when folk will drift away from the telly and turn the kettle on.

Same thing, a big hit on the grid

[Señor Chris]

If I have understood this correctly... if you charge batteries with an alternator only and no battery charger, the voltage steadily climbs to around 14.4v as the batteries become fully charged. I have read elsewhere that continuing at this voltage damages the batteries so what do you do on a long cruise? Without a charger, the voltage won't reduce to a safe float level. Would car batteries get damaged on a long drive for similar reasons?

[nicknorman]

If I have understood this correctly... if you charge batteries with an alternator only and no battery charger, the voltage steadily climbs to around 14.4v as the batteries become fully charged. I have read elsewhere that continuing at this voltage damages the batteries so what do you do on a long cruise? Without a charger, the voltage won't reduce to a safe float level. Would car batteries get damaged on a long drive for similar reasons?

14.4v doesn't significantly damage the batteries unless it is kept on 24/7. Even on a long cruise it's likely that the batteries will only just about be fully charged. So cruising for 12 hrs and then using the batteries for 12 hrs, repeat next day, isn't bad for the batteries. Having them on 14.4v 24/7/365 will shorten their life due to plate erosion, but it will take a while. Also it will cause them to gas and lose water.

 

Modern cars do tend to reduce the alternator voltage once the batteries are charged, but even without that it's pretty difficult to drive more than say 12 hours per day on a repeating basis.

[dmr]

If I have understood this correctly... if you charge batteries with an alternator only and no battery charger, the voltage steadily climbs to around 14.4v as the batteries become fully charged. I have read elsewhere that continuing at this voltage damages the batteries so what do you do on a long cruise? Without a charger, the voltage won't reduce to a safe float level. Would car batteries get damaged on a long drive for similar reasons?

 

Its not really a significant problem and the batteries don't get damaged. If they are "open" then they might loose just a little water which will need topping up from time to time. Obviously if you don't top them up then they will get very damaged.

Sealed batteries are a bit more of a risk but these most likely have calcium in their plates which reduces water loss. Car batteries will also be calcium so don't loose water. So boats and cars don't really need a float mode on the alternator. Float mode is only needed on a mains battery charger that is left on indefinitely, and most chargers go into float to soon anyway which does more harm than good on a "cruising" boat (rather than one that lives in a marina).

 

I guess that trucks that are in use for very very long hours might be a bit different, dunno if anybody builds a float capability into those.

 

.................Dave

[Tony Brooks]

 

 

Only just started running at over tickover the last couple of weeks, thought for some reason running above was bad for the engine.

 

I do have to admit that i fitted the new batteries, el cheapo from ebay, back in june, before i had the solar fitted, i think i may have done damage early on, to be fair though i went for the el cheapo route so i could understand how to kill a set of batteries, crazy i know but at £150 its not a big deal.

 

Going forward i do need to fit some better things to see exactly what is going on with my batteries through the day and when charging.

 

Looking at what i think is my alternator online, i can see i either have the 60 amp or 70 amp, so if we say 60 amp to be safe, i usually see my batteries touching 50% in the morning (using a cheap voltmeter wired into the circuit) thats with lights pumps and fridge running for the last 12 hours, if i run my engine for hours then i should be seing the batteries rise to at least 90%, is this fair to say?

 

 

It is running a diesel engine lightly loaded that might or might not be bad for the engine. Much depends on design details, oil in use and so on. In the early stages of charging you may have to run a 1500 rpm or more to reach maximum charging current but as the charge progresses and the batteries start to limit the charge the speed that gives maximum charge will reduce. On my boat it drops to around 1000 rpm within half an hour.

 

It is better to load the engine so by keeping the engine revs at the speed that gives maximum charging current when tied up will also give you all but maximum load.

 

You will not be able to run at maximum charging current without excessive revs until you can monitor the charging current so you will probably waste a bit of fuel by revving faster than needed but you will maximise the charge and minimise the time required to charge the batteries.

 

I do not think fitting cheap batteries while you learn how to maximise their life is in any way crazy. far better ruin a £150 set than a £400 or more set.