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by'eck

Member Since 04 Apr 2011
Offline Last Active Yesterday, 10:23 PM
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Posts I've Made

In Topic: Sterling pro-charge ultra - settings?

Yesterday, 10:08 PM

I don't have this particular model but would just set to the max 14.8 volt absorb voltage (Preset 1 range) with attendant 13.6 float voltage. Stay away from custom settings though. Note that any of the outputs that are not used should be strapped to the one with the largest bank connected.

 

My 50 amp three output charger is set the same with all three batteries/banks sealed VRLA - no issues. 


In Topic: Engine / alternator speed to charge batteries

Yesterday, 09:51 PM

 

 

 

 

See what SirN says and what I tried to describe. 

 

Yes I agree with his analogy

 

Alternators are rotating machines and battery chargers are not. I suspect that modern battery chargers do note even use AC in their final stages unlike an alternator. I accept they may "chop up" an AC waveform to produce the voltage they require but the resultant current will only flow as pulsed DC. The electronics in a charger could monitor current flow and then later the voltage it produces to suit, an alternator can not do they, such active (as opposed to passive) control an alternator has is done by pure voltage regulation once a sufficiently high voltage has been reached.

 

Only referred to mains chargers to highlight its the battery that controls charge current acceptance.

 

I agree that the current flowing into a battery will be the product of the charging voltage v the battery voltage so at any given charging voltage the charging current will be proportional to the charging voltage and inversely proportional to the battery's state of charge  and this will be true for any source of charge.

 

If we take an old transformer/rectifier battery charger it will start charging at a lower voltage and this will gradually rise as the battery becomes more fully charged and the charging current drops. Eventually it may well be high enough to wreck the battery if left on for long enough. IN essence this is caused by the same principles that MtB and myself described. Modern multi-stage chargers must be regulating the voltage at a number of different values each commensurate with the battery's state of charge but if this regulation during the bulk phase is by active electronics or by a passive effect such as I described I have no idea. The old chargers are very like an alternator in that their output is rectified as the current leaves the   device.

 

I think you will find adaptive charging aside, multi-stage mains chargers and external alternator regulators are simpler than you suggest. In the bulk phase they squeeze in as much current as they can as dictated by batteries, often but not always their max rated current, until the absorb voltage is reached. The time before this voltage is reached may vary enormously dependant mainly on battery capacity, max charge current available and DoD. It could be a matter of seconds if batteries are already fully charged.. When this, often user selected absorb voltage is reached a timed or otherwise limited absorb phase is triggered usually reflected by LED indications. It can be seen throughout the bulk and absorb phases the charge device is working in the same way but voltage limited in the latter phase before dropping to the lower voltage regulated float mode. So in essence they have two voltage regulators and a timer.

 

Nick, I would suggest that the resistance of the rotor is a design feature and bears little if any relationship to the reduction of charging voltage when the alternator approaches its designed maximum output. You will see I ignored the rotor and concentrated on the stator where there is an AC flow. Until the voltage regulator starts working the rotor is saturated with a current flow "turned fully on" so it is rotor resistance and whatever output there is form the field diodes that control the strength of the field but it will be fully or almost saturated. Any control of voltage at that time has to be caused by something else as I described. Of course once the regulator starts turning itself on and off the pulsing rotor field will have some effect on its degree of saturation but that is not what I was talking about. This effect would be allowed for at the design stage.

 

It is important to differentiate between what is going on re the rotor and what re the stator.

 

I agree but considering the latter alone, as its stationary back emf cannot exist, much like it can't with a stalled motor.


In Topic: Engine / alternator speed to charge batteries

Yesterday, 08:00 PM

Rather than consider back EMF in a motor sense and tangling your fingers round Fleming's rules, think of the stator as being more analogous to a transformer secondary and subject to heavy amounts of self induction, which I think is what Tony is describing. By the nature of inductance a magnetic field burgeoning as voltage rises will by its movement relative to the conductor induce an EMF in the conductor polarised to oppose the current in the conductor causing the current. Thus the current lags the voltage and is itself limited by the strength of the opposing EMF of self induction. This effect becomes greater as current rises and, here's the rub, with rising frequency. So both higher output currents and higher rotational speeds make it harder for the alternator to make headway and it runs into a law of diminishing returns where more field strength (even if not saturated) or more speed becomes more and more self defeating until a limit is arrived at.

 

Yes that makes more sense - thanks


In Topic: Engine / alternator speed to charge batteries

Yesterday, 04:46 PM

 

In the light of your wish I think Nicknorman was trying to keep it simple. I think that the term resistance in the second paragraph should read reluctance or inductance as we are dealing with AC current and pulsing magnetic fields.  As the current in the stator rises so does the strength of the magnetic fields it produces. As these pulse in and out they induce a back EMF in the stator that depresses the stator voltage. The degree to which it is depressed is proportional to the strength of the current and thus the magnetic field in the stator. Hence as the charging current rises towards the design maximum the charging voltage starts to fall until the lower voltage can just push the design current into the batteries.

 

As the batteries charge the charging current falls as does the bcak EMF so the voltage  increases until it is sufficient for the regulator to start to work.

 

This is why in theory it should be impossible to burn out an alternator. It will never produce more current than it was  designed to do. However other things like incorrect handed cooling fans, excessively low speed, or high ambient temperature tend to cock this nice theory up.

 

Not sure I agree with that Tony as I've said before. If your explanation of charge current and voltage from an alternator were true why does a mains battery charger work with the same charge current/voltage characteristics? Answer I believe is that its the batteries being the common denominator, that control the charge current acceptance and hence charge voltage, not caring where the charge current comes from. 

 

Its well documented that back emf doesn't exist per se in a generator since the back emf as seen in a motor is in fact the output emf in a generator so not referred to as such. Lenz's law is upheld by the need for torque applied to the rotor to resist the effect of the magnetic flux caused by the induced emf.

 

Surely alternator stator core dimensions dictate the nominal output power by way of flux saturation with the windings dictating the nominal voltage limited by the regulator, hence the current is also controlled.


In Topic: Immersion Heat up time

Yesterday, 03:38 PM

Two hours to comfortably warm.