13.7v Regulators
#1 _Yella SLuR_
Posted 24 June 2006 - 06:34 PM
Just thought I'd share the info.
#2 _devilsadvocate_
Posted 24 June 2006 - 07:01 PM
#3 _Yella SLuR_
Posted 24 June 2006 - 07:35 PM
I wasn't at my brightest this morning....damn soccerroos.
Edited by Yella SLuR, 24 June 2006 - 07:37 PM.
#4 _devilsadvocate_
Posted 24 June 2006 - 07:49 PM
#5 _TORANASS_
Posted 27 June 2006 - 12:08 PM
John
#6 _devilsadvocate_
Posted 27 June 2006 - 10:07 PM
Im not sure however, what constitutes a modern battery. The typical lead acid battery is still the same as its ever been? and one would assume that they worked out what voltage would be best to charge it with years ago too. A modern battery may be a zero maintenance battery that has slightly different charging requirements, I believe current model cars have the higher volt reg.
Certainly the 14.7V reg would end up overcharging a reg battery, unless there was a very high resistance between the batt and alt. If the car is not seeing much use and short trips, then the 14.7 reg would possible keep the standard battery better charged then the 14.1V reg and prevent those winter flats but overcharge in the heat of summer.
Im sure Dangerous and Hotrodder can fill in the gaps on this matter
#7
Posted 28 June 2006 - 01:44 AM
Edited by rodomo, 28 June 2006 - 01:52 AM.
#8 _devilsadvocate_
Posted 28 June 2006 - 08:37 AM
It is difficult to understand how an alternator could maintain 15V across a shorted battery, basically connecting the +ve of the alternator to ground.
How does the regulator know that the extra current load is due to a undercharged battery or simply that the headlights have been switched on? Perhaps this can happen in modern cars? where the computer can also monitor the battery but have no experience poking around looking at regulator outputs on modern cars.
Certainly some regulators change behaviour when they are cold/warm
My observations: regulator output will stay at rated output and only drop as the current load on the alternator increases(which is perhaps more due to alternator performance), consequently a fully charged battery will see maximum regulator voltage when current load on the alternator is small.
Edited by devilsadvocate, 28 June 2006 - 08:40 AM.
#9 _Yella SLuR_
Posted 28 June 2006 - 10:55 AM
Yes, I believed that regulators are an on/off thing, the only thing they regulate is the additional current generated from a reving engine. Never really understood where the excess energy went though.
Edited by Yella SLuR, 28 June 2006 - 10:55 AM.
#10 _devilsadvocate_
Posted 28 June 2006 - 11:11 AM
This is from the idea that an alternator creates a constant load on the engine, the load actually varies with current.Never really understood where the excess energy went though.
If a alternator rated at 80A has a load of only 10A on it where does the other 70A go? into heat, the alternator would have to go red hot to release that amount of energy.
Simply, if the load is only 10A, the alternator only requires that much energy from the motor to turn it(a little bit more since the conversion of mechanical energy to electrical is never 100%), there is no 70A of current to get rid of.
#11 _Yella SLuR_
Posted 28 June 2006 - 11:18 AM
#12 _TORANASS_
Posted 28 June 2006 - 11:30 AM
Sure on longer trips or night driving you need more from your battery so the alternator has to compensate for that, thus drawing more energy from the motor and generating a higher current to keep the battery charged.. Thats why i dont see that an extra .3v would do anything substantual in the charge of a battery..If this was the case why do they make alternators with higher AMPS.. Surely a 70A alternator would charge a battery better then a 40A unit.
John
#13 _devilsadvocate_
Posted 28 June 2006 - 11:46 AM
a 0.3V difference over (13.8-12.6) will create a theoretical 100*(0.3/1.2) % = 25% difference in the current applied to the charged battery, less if the battery is undercharged.
The numbers ^ are simplistic but should give a basic idea, and dont take into account the particular threshold/critical voltages needed for charging to effectively take place with different electrode combinations.
No, a 70A alternator wont charge a battery better than a 40A one. There is a limit to how much current the battery will draw on charge, if its a large battery thats very flat it will initally accept most of what the alternator can throw at it. Typcially your normal battery wont accept more than 25-30A of charge for any appreciable length of time while recharging. High alternator capacities are really there for high accessory loads.
Edited by devilsadvocate, 28 June 2006 - 11:47 AM.
#14 _TORANASS_
Posted 28 June 2006 - 02:19 PM
Cheers
John
#15
Posted 28 June 2006 - 02:29 PM
My understanding of the alternator/battery relationship is very similar to yours.
The part I always have trouble undestanding is, if the voltage regulator, 'regulates' or 'limits' the peak output of the alternator, why does the voltage go skyward (up to & over 20V) if the battery is disconnected whilst the motor is running.
Dr Terry.
#16 _devilsadvocate_
Posted 28 June 2006 - 02:46 PM
I dont know the answer to your quest, im guessing that the load presented by just running the ignition on a running motor isnt enough to make the reg function properly, this could easily be verified by seeing what happens if you make sure there is an additional load of about 10A present, maybe dont use the headlights if its going to go 20V! Let us know what happens!
Edited by devilsadvocate, 28 June 2006 - 02:58 PM.
#17
Posted 28 June 2006 - 04:17 PM
This is a common problem I've seen over many years on many cars.
The usual scenario is when a guy doesn't have a battery fitted to the car, for whatever reason, then jump starts the car using another car, disconnects the jumper leads & then attempts to drive the car home. By the time he gets home he has blown several globes & maybe even damaged some other hardware (car radio, engine ECU etc). Upon inspection the charge rate has gone ballistic (20V & over). Fit a good battery & all is OK.
The 2nd scenario is even more common, where the guy jumps starts the car because he thinks the battery has just 'gone flat', but in fact it has gone open circuit, so when the jumper leads are removed, the previously described disaster occurrs. This is the basis for many of the myths regarding the 'spiking' of engine ECUs.
Dr Terry.
#18 _devilsadvocate_
Posted 28 June 2006 - 06:17 PM
Edited by devilsadvocate, 28 June 2006 - 06:27 PM.
#19 _TORANASS_
Posted 28 June 2006 - 06:59 PM
Ever tried to run a car stero on a battery charger, ZZZMMMMMZZZMM ZZMMMMMMM XXXRRRR ZZZZMMMMM you get plenty of AC Hum..
John
#20 _devilsadvocate_
Posted 28 June 2006 - 11:53 PM
#21
Posted 29 June 2006 - 10:01 AM
To my knowledge all automotive alternators are 3 phase with full wave rectification, so their output is quite smooth for something that's not filtered. In a fashion, the battery acts as a large capacitor to filter out the remaining 'spikes'.
I know when you drive a car with the battery disconnected, as described above, the 12v noise on the car radio is really bad.
Dr Terry.
#22 _TORANR AMORE_
#23
Posted 18 July 2006 - 02:59 PM
DA, I pretty much agree with your thoughts on higher battery charging voltages. 14.7 volts with no loss works out at about 2.45 vpc, which is at the upper limit, but not deadly to batteries.
Rodomo, if an alternator is continually pumping out 15 volts, it's more likely that the battery is open circuit or high resistance on a cell. 15 volts constantly into an otherwise healthy battery which would have an extremely low internal resistance equates to a bloody lot of power and heat. It would probably boil the battery pretty quickly, unless the alternator or regulator fried itself beforehand. Higher charge voltages when the engine is first started can be a good way to initiate charging for the battery though, but I am not aware of any alternators that are specifically designed to do this - it can happen by default though straight after the engine fires, as the battery voltage is down due to cranking load, and the alternator gets spun up, sees a very low battery voltage (which equates to a low resistance load for the alternator), and then pumps out max output until the battery voltage comes back up to a reasonable level. I wouldn't have thought it would be as long as 15 to 20 seconds though.
Yella, think of the alternator as just another engine - your engine might be capable of 300 hp, but how much it actually puts out depends on the throttle setting - the regulator is the throttle setting for the alternator (engine).
Dr Terry, the battery acts as both a smoothing load (capacitor) as well as a reference voltage to the alternator. If the alternator loses the load (battery), it can't reference its output voltage, and it tends to head to the maximum voltage it can make. This is limited and lessened by the electrical load on the alternator. In my (unfortunate) experience, this is around 18 to 20 volts with a car driving when a battery lead came off, but I think it can get as high as 30 volts with no load, which is probably enough to pop all the diodes in the alternator. DA, you're right, once started by battery voltage on the stator, the alternator can feed itself, which is why a car engine will still run if you just isolate the battery +ve cable.
ToranaSS, I think maybe you're wrong on the alternators, and right on the cheap chargers. All recent alternators (including those of the Torana era) are multi phase and full rectified. Some cheap chargers are only half wave rectified though, in a really cheap and nasty way to regulate charge current. The peak voltage of the half wave rectification is above what it should be to charge the battery (eg the peak voltage may be 16 volts, but the battery only wants to see ~14 volts), so for a flat battery, the cheap and nasty charger still puts out 4ish amps to charge the battery - it still charges OK. As the battery becomes charged, the peak voltage from the charger still exceeds what the battery likes to see, but it's only on for a short time on the peaks of the half wave regulated waveform, where the voltage exceeds the battery voltage. As the battery voltage comes up, there is less power (area under the half wave peaks down to the DC voltage of the battery), so it sort of self regulates ..... sort of. Definitely a good idea not to leave a cheapo non charge state monitoring charger on charge for longer than you have to.
Toranr amore, can't get to that link, but I'll check back later - might be some good reading.
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