Electronic load idle up - 20v 4age

[oldcorollas]

basically an alternator, when spinning fast enough, will produce it's regulated voltage between the sense pin on the back of it, and the B+ post on the back of it...
that is all it does.
where you get the sense wire, and where you put the B+ wire, and how well the alternator case is grounded all determine how much of that gets to the battery and your stuff

[wilbo666]

I did this up to try and make it clear


And this post previously.
http://www.toymods.org.au/forums/sho...1&postcount=27



Cheers
Wiblo

[thechuckster]

thanks wilbo! pictures = much betterer

pauljones1976: the regulator doesn't just turn charging on/off - instead it regulates the voltage output depending on the battery condition. Amperage output is directly-related to that voltage (e.g. if the battery is flat, it will pump out a lot of amps) but amperage also varies according to shaft rpm of the alternator.

[pauljones1976]

Thanks guys, it all makes sense. I haven't checked the voltage at the B+ terminal yet purely due to being slack. I know, there's really no excuse!

I'm pretty sure I get the whole concept here. P=IV right? So V=P/I.

Am I right to assume that once the alternator is ON it produces P (power) relative to the spin speed. Then this power (P) which is made up of = I (current or amps) multiplied by V (voltage) is regulated in relation to the V (voltage) with respect to the voltage in the cell/battery/circuit depending upon where it's measured from (S - voltage sense).

So, if the alternator was spinning fast enough to produce 14W of power and (S) voltage sense was measuring say 14V then the alternator would put out 14V @ 1A which would provide 1A of current through the circuit (or 14W of power) but not charge the battery due to the potential difference between the battery voltage (S) and the alternator voltage (B+) not being enough to charge.

In the same scenario (alt producing 14W - P=14W) but the (S) voltage sense was measuring 12V then what you guys are saying is that the alternator regulates the voltage > (Greater than) 14V - say for instance 16V @ 0.875A (14W = 16V * 0.875A) - thereby charging the battery.

All this being said, would an alternator *ever* charge at a voltage below 14V, regardless of what the voltage was at (S)?

ie: What circumstance would cause an alternator to regulate it's voltage below 14V?

I'm pretty sure my problem is related to the alternator not producing enough power (P) so I'm not too sure how the (S) voltage sense would affect this.

I'm not trying to be a pain, just trying to understand a little more how the alternator actually works sorry if I've offended anyone, I really did not intend to.

[wilbo666]

Am I right to assume that once the alternator is ON it produces P (power) relative to the spin speed.

Not really.

The Alternator produces power relative to the spin speed (rpm) AND the Field Coil Current.

And the field coil current is set by the regulator based on the battery voltage!!!

I.e. If the battery voltage is low, the regulator increases the Field Current, which makes the alternator harder to 'turn' (More magnetic field) and hence the alternator produces more current which is used to charge the battery - if you can turn it at the same speed...

http://www.alternatorparts.com/under...lternators.htm

Cheers
Wilbo

[thechuckster]

not quite - it regulates the voltage output to around 14V (open to corrections here). If the battery is at 12V it pumps out more amps (not volts).

(looks at the nearest haynes manual) ... For a Denso/Bosch 40/50A unit from a 22RE, it produces at least 10A at 2k engine rpm at 13.5-15 volts at the B terminal (the large terminal providing the charge output).

If the voltage is under 13.5-13.8 (depending on model) the alternator has issues (diode pack or windings or brushes). If it's over 15V, its the regulator.

When loaded up (e.g. lights on High, fan on, wipers on) the same alt produces well over 30A at the same revs (2k).

With a larger unit (e.g. the generic ford/bosch 80 A unit), you would up the current output at the same speeds and at idle it would be able to deliver a substantial amperage.


Why the voltage sense (S) is so important? That's the signal that the alternator uses to judge battery condition (in voltage). And the alternator cant shove higher voltages into the system as a) things may loose their stored electrical smoke, b) it's not going to charge the battery.

It's able to vary the current output to the B terminal based on the S terminal. Power output is not a direct linear relationship to shaft rpm.


edit: damnit - beaten by wilbo again.

[oldcorollas]

All this being said, would an alternator *ever* charge at a voltage below 14V, regardless of what the voltage was at (S)?

ie: What circumstance would cause an alternator to regulate it's voltage below 14V?

YES, IF THE ALTERNATOR IS NOT SPINNING FAST ENOUGH


an alternator only "regulates" below 14V if it's design voltage is lower (like 13.8) or if it is fucked.


get multimeter, do the rpm test i described and report back.

[thechuckster]

I'd also like to apologize to GEMTA22 for this thread hijack ;-)

[oldcorollas]

i got confused as to which thread was which

rough alt power curves.. at low rpm, a small cahnge in rpm makes a BIG difference between having any output.. and not..

[pauljones1976]

Thanks guys, I now understand this 'field current' concept somewhat - you've all been very helpful. I think I'll have to have a look through my old electrical textbooks and look it up but it certainly makes sense. We learned a lot about the rectification of alternators but not anything that I can recall about field current.

I asked a mate who is an auto electrician about the (S) connection, he said just hook it to the B+. After learning all this stuff, I'm now stumped as to why he suggested that and am wondering how someone manages to become an auto-electrician and not understand such a basic principal.... I'll definitely hook that (S) connection directly to my battery now. I'll also strap the alt housing to the chassis to ensure my ground is up to scratch.

So I guess the real question now is what can be expected of this alternator at idle speed (approx 900rpm) and whether it's enough to drive the load I am requiring.

I'll get onto that test tomorrow as soon as I get back from work and see what's going on. I will report back with more info tomorrow! Thanks again guys, and thanks for setting me straight on my electrical knowledge!

[pauljones1976]

Well today's the day to get these tests done on my alt. Finally I have a little 'daylight' hours to start the little red thing up!

Of course, I've been doing some resarch and have found some interesting information regarding the (S) voltage sense connection.


Here is an article where a couple of guys have hooked an alternator up to a bicycle to investigate how they operate

In it, it states:
"we determined that there are four connections that must be made to an alternator: 1) ground (the case), 2) positive (a post coming out of the top of the alternator), 3) the alternator's field, and 4) the alternator's regulator.

During operation, charge flows from the alternator to the battery through the positive post. The field is connected to an indicator light or resistor and then to the battery's positive terminal. This supplies the initial charge that the rotor needs to produce electricity. It should only be connected during operation (to avoid running the battery down) and, in a car, is connected through the ignition switch."

"At first, we just shorted the field connection directly to the battery's positive terminal. There are two reasons this should not, in practice, be done. The first is that this results in a very large current flow. We measured 3A flowing through the field connection with the car battery connected. Although the current flows only for a brief period of time, it can be too great for a lesser quality alternator to handle, and can blow the field coil apart."


So these guys are referring to the (S) Voltage Sense connection as the "Field Current Supply". What they're saying is that the non-switched connection of the (S) connection on the alt directly to the battery will cause current to flow constantly through coils in the alt regardless of if the car is on or not. They are also saying it may damage the alt although i find that unlikely if the wire is small - but then again, I guess the wire could burn out and arc on the chassis if it were too small....

What I'm mostly concerned about is that if I connect my (S) Volltage Sense directly to the battery it will drain my battery when not in use. My car sits in the garage for up to 2 months at a time without use AND the boot has NO EXTERNAL RELEASE MECHANISM - it's battery operated and has no key. If my battery goes flat, i'm in a little bit of trouble getting to it

Can anyone conrfirm/deny this problem(s)?

[toymaz]

The alt they play with is and external reg, your an internal reg
if you connect the batt sense wire to perm batt- ie the alt post next to it, yes it will drain the battery
I only do this when testing alts on the bench...
connect it to a switchable sourse like ign
while we are here my 4ag20v runs a microleb also, 2 x efi pumps, 16 inch thermo and headlights
does not have a problem with stalling. I think its possibly in the tune, im sure there is a fucntion for extra fuel at voltage.
cheers
Brad

[pauljones1976]

Ok, results of tests today!

Voltage at B+
Ground at Chassis front of car

No Load
at 2000+RPM = 14.4-14.6V
at 1050+RPM = 14.4-14.6V
at 950RPM = 14.0-V
at 850RPM = 13.5V

Lights on
at 2000+RPM = 14.4-14.6V
at 1050+RPM = 14.4-14.6V
at 950RPM = 14.0V
Once the voltage drops below 14.0V the revs drop away down to about 500rpm and lower and HUNT and the voltage drops down below 12V. Car stalls if voltage drops below 11V.

Lights and Brake Lights on
at 2000+RPM = 14.8-15V
at 1100+RPM = 14.5V
at 1050+RPM = 14.4V
at 1000+RPM = 13.9V
about now is when it starts to hunt.

Interestingly at 1250+RPM when I turn on the blower fan, on speed 1 I get 15.1V, speed 2 I get 15.8V, speed 3 I get 14.4V. (where 1 is the slowest, 3 is the fastest)
Any ideas what could be causing this fluctuation? Could it be a short in the blower fan motor or worn out windings or something?

And why is my REG not sitting the voltage at 14.4V??? (it's increasing slightly when under load)

[toymaz]

Are these voltages same @ battery? you may find them to be more stable at the battery.
no problem with volt going up or down slightly, if your vehicle startes to run crap when volts get down to below 14v, sounds like your ecu needs some fine tuning.

[oldcorollas]

perhaps your chassis is not a very good ground?