Time taken to charge batteries VS alt size.

There are alternators that do produce at low rpm like ones used on earth moving equipment.
Direct connected ones on Detroits only run at engine rpm for example.
( Althought these days they use internal step upgears to get to 6000rpm)

But I agree with Pistnbroke many many installations never work correctly as the alternator is running too slow ( automotive ones)closely followed by ones that never fully charge the battery due to low max voltage settings.

Std internally sensed and or with diode bridges are a classic for low battery life as they never get charged
( Smart regs have fixed this issue)

Followed by missmatch of belt section and pulleys so they slip before they get to max voltage ( not current, so people with ammeters think they are charging their batteries)
You need a strobe or a diesel timing light to check this one.
Serpentine/poly vee belts fixed this

Another problem I see is in large parallel banks the pos and neg feed/supply are on the same battery and all the others paralleled off this.
Not good, they need to be at opposite ends of the bank.

I wouldnt look at a problem until I had the output/rpm curve in my hand. Prior to the internet all the big brands Delco/Hitatchi/Leece Neville etc would fax them to you. I'm always surprised its rarely done?
To finish a job I would make a time/rpm curve so the owner knows how long it will actually take to charge his batterys from flat , i.e. 12v ish reading
( and that will change over the life of the women..I mean battery as mentioned above)

 

well I'm an elctronics engineer with a background in bettery charging systems.

Firstly the Charge Acceptance Rate is a value set by the battery manufacturer and its the maximum value that the battery can be charged at. Note desite some posts, its NOT the maximum the battery can be given, thats the problem with lead acids, they dont know when to stop.

Typical CAR's for average batteries are betwwen C/10 to C/5. Hence your alternators should be sized to this ( plus about 20%) 25 A per 100ah is C/4 and is on the high side.

The Best charging profile for lead acids, is IUI, thats is constant current , followed by constant voltage follwoed by a float trickle charge, ( constant current). These are technical terms

In practice, standard car alternators , and by that I mean their regulators are not good charging systems, they are primarily designed to run the cars electrical needs not charge batteries ( much to most peoples suprise) hence the voltage tends to be lower at around 13.8 to 14V. This doesnt propoerly charge batteries.

The sequence for best charging is

(a)Initial Bulk phase, constant current, battery resistanance is low and the battery should be supplied with current to CAR ratings. Most alternators can do this.

(b) As the batteyr terminal voltaage rises, a proper charger will raise the charge voltage , ensuring that max current is delivered to the battery, at a certain point around 14.4-14.7 , the charger will cease to raise its voltage and enter a constant voltage phase, This is the absorbsion phase.

(C) This phase continues in order to top te battery up , typically at the start of absorbsion phase the battery is at about 80-85% charged. This where standard auto regulators fail , they cannot handle absorsion voltages.


usually termination of the absorbsion phase is based on the current accepted by the batteries falling below a certion value. or a timer expiring ( as a safeguard). One of the problems with IUI charging is if the cell is faulty the charger can stay in absorsion mode for too long and boil the batteries as some gassing does occur in absorbsion mode.

After absorsion mode is terminated the regulator lower the output current to a trickle charge .

Most alternators are designed to output full power with the enggine at about 1200-1300 revs, after that the regulator does not produce any more current. Theres no need to run flat out.

Standard automotive regulators and alternators will not cope with high current demands over long periods, the alternators run too hot. Anyway alternator output falls with increasing temp, so derating is needed ( hence the 20%).

Anyway its time to dump lead acid technology LiFePO4 is the way to go.

Dave

 

No argument with the abc's smart regs do that job very well.

Assuming the pulley ratio is 3:1 I'd like to see an output curve of an automotive alternator showing max output at 3600-3900rpm? Most I can find need alternator rpm of 6000+

The regulaltor doesnt make current it only limits output by cutting power to the rotor which lowers the voltage yes?

How does the charging profile of a LiFePO4 battery look like, do you still need smart charger type charging profiles?

Cheers

 

quite right power about regulator regulates the max voltage and 25 A per 100ah is c/5 + 20 %.......

alt should be geared to 12000 rpm at engine max rpm ....so that at more normal revs its going fast enough.....

 

Thanks for the very informative posts.

Can I disable the regulator in a standard alternator and use a more advanced regulator?

 

Yes but sometimes its not so easy as the regulator is built into the brush holder.
Usually the companies that make the smart regulators have instructions to install them to all the common alternators.
Dont forget to get your output/rpm graph for your alternator and then do the pulley ratio calculation on what rpm you need so that you actually get what you expect.
Cheers

 

Can anyone recommend some smart reg brands that might suit my application?

 

dennis this final float stage is great for chargers connected 24/7 but in a boat situation that does not happen and you are always pulling the batteries down with loads or leaving them idle ...forget it just ensure your regulator gets them up to 14.4 -14.7v

 

Thank goodness someone else can see through the smart charger scam, float charging is all they really do but it never gets used, it can't do where loads are supplied and running times rarely warrant it and in any event a bit of overcharging is beneficial for equalising and desulphating if that did happened.

Smart chargers cost two or three times the alternator cost, if they were really needed then the alternator manufacturers would surely fit them! The ordinary regulator simply limits the maximum charge voltage to give the minimum or maximum charge rate required within the battery limitations of heat, gassing and charge time.

Smart chargers do not have any extra benefits over the correct voltage regulator for the application. It is also a fallacy that a lower charge voltage prevents batteries from being fully charged, it just takes longer. It is also a fallacy that self limiting alternators and regulators cannot handle a constant full output or that regulators carry load current. Car voltages are typically 14.2 to 14.6, lower voltages are only used for stand alone and little used starter batteries such as on a generator or other plant.

Regulators of any sort do not play any part during the so called bulk charging phase where maximimum alternator output is absorbed until the battery voltage rises and the regulator then starts to limit the alternator voltage and corresponding lower charge current at the same time as supplying any loads at the regulated voltage. It's as simple as that and always has been long before someone thought they could do it better and make a fat living out of it.

 

and so say all of us ....

 

Oh well perhaps I need more than 50 years working electrical experience and need to go back to college yet again! Won't change the facts though.

 

I totally agree with you cpt littlle legs ..if the boat has a mains charger connected when in dock then going to 14.7 and dropping back to 13.8 is ideal but not neccessary in an engine driven cruise /anchor situation. Most boats seem to have a problem running thhe engine long enough to get them fully charged never mid floating ...If you are running the engine to charge the batteries and they need to be floated then its time to turn the engine off. If you keep running you will not do them any harm considering the likley running hours.

 

Exactly, most batteries will be in some state of discharge most of the time with onboard loads unless on an extended motoring trip and due to the time involved, charging in the dock on shore power is where most batteries will economicaly get up to full charge.

 

I just thought a better reg would get the voltage up to 14.5 ish volts. Right now it only sits at 12.5 volts when batteries are low and it will slowly go up to high 13's after hours of charging. I need to do some more measurements to see if there is 14.5 at the alternator in case the wiring is too small. This is all good and well but when I get out there I just drink a lot of beer and couldn't be bothered getting the multimeter out in the engine bay. I really need to get my arse into gear.

 

A good shore power connection and a sufficient sized continuous marine marine battery charger should also be part of the equation.