voltage regulator using a TIP 102?

Thread Starter

kano

Joined May 6, 2009
8
hi, i have a busted voltage reg. unfortunately, no replacement can be found here in Yemen so i decided to take a look inside. I found it to be a transistor TIP 102. I tried to figure out how it was built but i destroyed the pcb and other parts in the process of removing the plastic covering that is so thick. Can anyone help me how to build this regulator? It's for an alternator supplying 27v for charging 2 pcs of 12v acid lead batteries. I'm sure my boss will give me a raise if I can accomplish this. thanks.
 

MikeML

Joined Oct 2, 2009
5,444
How much field current does it take to excite the alternator?

Are both ends of the rotor (field winding) accessible (i.e. two field terminals, or only one)?

If only one, where is the other end of the rotor winding tied? Gnd or the alternator output?
 

MikeML

Joined Oct 2, 2009
5,444
What power transistors (NPN, PNP, NFET, PFET) do you have to work with?
What voltage references (Zener, LM431) do you have to work with?
What opamps do you have to work with?


TIP102
 
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Thread Starter

kano

Joined May 6, 2009
8
regarding your first question, i have no idea, but when i flash it (excite it with just a touch), i get 26.something volts, just about the same voltage for 2 12v connected in series. Yes, the 2 terminals are accessible, one is connected to the body and one to the starting switch. It's an NPN darlington chip.
Realizing that the alternator produces just about the same voltage as the voltage of 2 fully charged batteries should have, the transistor must be acting only as a switch, and not really regulating, well, being a newbie, all i can do for now is guess until someone passes his lighted candle to me...:confused:
 

MikeML

Joined Oct 2, 2009
5,444
I am very familiar with 14V and 28V 60 to 100A alternators used in aircraft. These typically have an external voltage regulator (VR), unlike modern car alternators where the VR is built inside the alternator.

VRs work by sensing the battery voltage, comparing it to the a reference voltage (zener or band-gap reference chip like a TL431), using a comparator which drives a switching transistor (Like your TP102) to pulse the field (rotor) current on/off. It is in effect a Pulse Width Modulator. The field has so much inductance that the PWMed current through the field is "smoothed".

The output current of an alternator is proportional to the rotor RPM and the field current. The DC resistance of the field is ~15Ω, so with full-on 28V excitation, the field current is less than 2A. The PWM reduces the average field current to under 1A under normal load at normal RPM.

I can supply you with a schematic of a VR, but without knowing what parts you have on hand or can get easily, this might be a futile exercise. Another possible solution is to get a 14V VR from a late sixties to early eighties Ford. These can easily be opened up and modified to work with a 28V alternator. Please advise...
 

Thread Starter

kano

Joined May 6, 2009
8
sorry, just came back from work. I would love to have an schematic for the VR, preferably the 28v. There is a decent electronic store here in mukalla, Yemen, but i didn't find the TIP 102. I did find however, it's equivalent, BDX53c but i blew it when i tested it with a charger, it blew when i switched it off, maybe it's the inductor trying to maintain current? This alternator by the way is used on a northern lights lugger engine powering the generator for a fishing boat. And thanks for sparing me some of your time...:)
 

t06afre

Joined May 11, 2009
5,936
try BD 649, BD 901, BDW 73C...D, BDX 53C...F But I guess the error is somplace else, and that fault caused the TIP 102 to blow. So the TIP 102 is a secondary fault.
 

Thread Starter

kano

Joined May 6, 2009
8
these fishermen usually take out the batteries to start another while the engine is still running, could that be the cause? I really need an schematic so i can make the regulator myself.
 

MikeML

Joined Oct 2, 2009
5,444
these fishermen usually take out the batteries to start another while the engine is still running, could that be the cause? I really need an schematic so i can make the regulator myself.
Yes, disconnecting the battery with the alternator charging can create a what is known in the industry as a Load Dump. Imagine that the battery has a charge deficit, due to using house lights or due to cranking the engine. The engine is started and is running at a fast idle or higher RPM. The VR cranks up the output of the alternator so it is delivering >~30A to the battery.

If at that instant, the battery is disconnected, think of the alternator as a current source with a compliance of ~150V. Just like when a current-carrying inductor is suddenly open-circuited, the 30A will continue to flow, but now the battery is not there to absorb the current.

Even though the VR senses the rising output voltage, and cuts off the field current, because the inductance of the field is several Henrys, it takes >~1/4sec for the field current to decay to zero. During that 1/4s, depending on system load, the output voltage can soar as high as 100V. This can wipe out the diodes inside the alternator, or the transistor in the VR, as well as lamps, marine radios, sonars, fishfinders, etc. Never, Never disconnect a battery from a running engine

I'll dig around for a schematic of a home-built regulator that is on my hard drive, somewhere :confused:
 
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Thread Starter

kano

Joined May 6, 2009
8
thanks mike, for the enlightenment, and i'll be waiting for the schematic.
 

thyristor

Joined Dec 27, 2009
94
This the schematic of the very common Lucas A127 alternator. This a 12v version whose regulator switches at or around 14.2v. The capacitors are to speed up the switching.

Note the diode across the rotor - without this the output Darlington will be singing "Goodnight Vienna". Although the Darlington is represented on the schematic as two discrete transistors, in the actual regulator it is a TIP device.

The rotor on these and most automoble alternators is around 3 to 4ohms so full rotor current is of the order of 4 to 5 amps.
 

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Thread Starter

kano

Joined May 6, 2009
8
thanks thyristor, i'll try to build it right away. I can also use this on 28v right? I mean afterall, the chip can hold up to 100v max. if so, are the resistor values still valid? And what volts will i choose for the zener?
 
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MikeML

Joined Oct 2, 2009
5,444
thanks thyristor, i'll try to build it right away. I can also use this on 28v right? I mean afterall, the chip can hold up to 100v max. if so, are the resistor values still valid? And what volts will i choose for the zener?
The Alternator Control Unit (ACU) below is for 28V. The S input connects to the ignition switch. The A input comes from the alternator/battery. The F output sinks current to ground to excite the alternator's Rotor (Field). The other end of the Rotor must be tied to battery.

The parts are not too exotic. 15V Zener (can be 100mW), a couple of non-critical small-signal NPNs, and a 2N3055 power transistor on a heatsink. Note the 3A snubber diode which is effectively wired across the Rotor as Thyristor mentioned. The trimpot lets you set it to ~28.5V, the correct charging voltage for a 24V lead-acid battery.

I have simulated it. The second circuit is the test-set-up and shows how you would interface the ACU with the other bits. Note the waveforms, including the PWMing of the Rotor current.
 

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Thread Starter

kano

Joined May 6, 2009
8
thanks again mike, i'll build this instead and make thyristors schematic later, since my target is a 28v reg. I don't think i will have any problem finding the parts needed. I'll let you know when I've succeeded. Looking at results of sim, i shouldn't have any problem at all as long as i follow your schematic.
 

thyristor

Joined Dec 27, 2009
94
thanks thyristor, i'll try to build it right away. I can also use this on 28v right? I mean afterall, the chip can hold up to 100v max. if so, are the resistor values still valid? And what volts will i choose for the zener?
You can use this on 28v but the resistor values and the Zener value will need changing. Try to analyse the circuit as shown in order to understand why the values need changing and to what value they need changing.
 

MikeML

Joined Oct 2, 2009
5,444
Here is a set up for Bench testing the 28V ACU or any similar unit. The goal is to get it to switch OFF as the voltage is swept upwards through 28.5V.
 

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