MK1/Eunos 1989 - 1998 were originally fitted with Mitsubishi units - 60 and 65 amp. All very similar with a 6 diode rectifier and regulator.
The 1.6 has a ‘V’ belt pulley and the bottom bolt goes through the two guides into a nut at the back guide, nearest the back of the engine. The 1.8 has a pulley for a ribbed belt and a thread on the front guide for the bottom bolt to screw directly into. It is easy to interchange pulleys, the 1.6 alternator can be fitted to the 1.8 using the 1.6 nut and bolt. The 1.8 alternator will need work on the bottom bolt to fit to the 1.6 as not room to fit without removing the inlet manifold support or drilling the guide thread out to use the 1.6 longer bolt with nut. The B+ main pole is too big on the 1.8 alternator for the 1.6 but just a case of running a drill bit through the eyed connector, enlarging the hole to fit.
MK2/MK2.5 1999 - 2005 were originally fitted with Hitachi units - 70 and 80 amp. From a fit point of view these are interchangeable with these cars. No issue with using an 80 amp alternator where 70 amp specified but may be a slight shortfall charge problem the other way around.
The LR170-758, 70 amp Hitachi LR180-766, 80 amp Hitachi are very similar units. Again there is a 6 diode rectifier and a regulator. This is the surprise for me - I always believed that the MK2/MK2.5 was regulated by the ECU. My MK2 1.6 bought with a water damaged ecu had a number of problems after the ecu was repaired - one of those was that the battery was not being charged. When I replaced the ecu this fault went away. I thought this was ecu regulator related at the time.
I’ve had a look at the components on the MK2 and MK2.5 ecu and there is nothing obvious that looks like an alternator regulator. After dismantling a MK2.5 LR180-766 alternator today I am confused. The unit has a rectifier and a builtin regulator.
My question is why, wattage ratings and small physical mods ignored, can’t MK1 and MK2/MK2.5 alternators be interchanged? They certainly can physically as the same as the MK1 1.8 unit. The theory in several historic posts is that MK1 cannot be fitted to MK2/MK2.5 and vice versa. Apparently fitting a MK2 alternator to a MK1 will result in unregulated voltage and possible damage. If my theory is right these alternators are all potentially interchangeable between MK1 - MK2.5 - comments please.
Hi Rob,I believe they cant interchange also.I had customer here one time, with mk2 1.8, that had new alternator fitted by Fast Fit type garage/tyre shop and it had intermittent issues with charging light coming on.Obviously it was not charging when light was on as I checked at battery.He paid approx 400 euro incl labour and they would not take it back as it was fitted !! By them.They said the motor supplier says there is only 1 type for mx5!!. But I fitted correct mk2 alternator and never issue after that so I do believe they are different. 4 years on it still working well. Does the small sticker on some alternators not say “built in regulator” or similar wording, on some models only?
I still have the “new” alternator I took off his car if you want to buy it and check internals.It as new ,only fitted approx week, but that was 4 years ago.20pounds plus postage?
I hope it’s nice over there in Ireland. Trying to weld my old Golf up as failed MOT but too windy here to weld outside.
Unfortunately I think you are right with the alternators but the difference has to be more subtle than a builtin regulator as they all have them.
All the original MK1 / Eunos Mitsubishi varieties had a label with builtin regulator specified on it. The Hitachi MK2/MK2.5 ones do not make that claim on their label but take it from me they have a regulator.
I do not think a MK1 alternator will charge a MK2/MK2.5 battery. A friend from Milton Keynes who breaks cars sold me an alternator that allegedly came off a MK2 car. It was a lovely condition part that I sold to a customer after doing the usual multi metre tests. He got in touch as his MK2 battery not charging. I sent a replacement out and the matter was resolved but later retrieved the non functional alternator. Took it apart last night and the rectifier/regulator are typical Mitsubishi, so I suspect this unit came off a MK1 1.8 car. The same is probably true of the recon alternator you have. By all means send it to me. I will test it on my MK1 1.6 along with my troublesome alternator just to prove the point. If it works, will pay you £25 for it to cover the part and hopefully delivery. If it doesn’t work will still cover the cost of delivery as enjoy playing with these parts.
With no further input on this thread, guess I will have to try a MK2 alternator on my MK1 car at the risk that the voltage may do some damage. Had hoped that someone had pioneered this before but as usual with my problems and questions am on my own:-) Would I have it any other way - probably not.
2005 Mk2 Arctic, low mileage lovely condition this was say summer 2011.
Car had the check engine light on and the ODB2 scanner found no faults.
Done the disconnect battery and push down the brake pedal.
Check engine light off but the car would not start on the battery.
Jumper leads and it started fine.
The charging voltage was 19.5 volts and removal of the battery it had a melted case.
Lifted the passenger side carpet and wet and rusty ECU.
New battery and dried out ecu and the charging voltage was back to normal and no further problems.
My guess is that the MK2 ECU controls the Mk2 on board alternator regulator from what you say rather than the ecu physically regulating the alternator internally in the ecu. The Mk1 on board regulator controlling it’s own alternator voltage.
That makes senses and the wiring to the ecu is not that thick and the ecu is in the wrong place to produce heat and get rid of it if it did physically regulate the voltage.
Yes, I agree - no way the ecu can take over the actual task of regulation but in later cars, MK2 and Mk2.5 it has control of the alternator regulator. This may be a complicated procedure where the ecu can basically turn the regulator on and off as well as making adjustments.
It seems that when the MK1 was manufactured this technology stopped at the alternator. Later cars incorporated the ecu as part of this process.
I assume this means that the MK1 Mitsubishi regulator will not talk to a MK2 ecu so will not work.
Not sure how this works with a MK2 alternator on a MK1 though - perhaps a lack of ecu involvement means that the charging voltage is not regulated as alternator regulator relying on instruction from the ECU.
This is a lot more complicated and sophisticated than I thought it was - nice to have some answers though
Not sure this helps of not! Eddie makes an assumption that the MK2.5 main output is regulated by connection directly to the ECU - not so. You regulate main output by altering the field strength, that applies to any regulator, including old school DC regulation. Field regulation does not require heavy conductors or heat dissipation.
Unfortunately I’m stuck between a Mk2 mechanical Manual and a Mk2.5 electrical one, with neither having any description on how regulation is achieved.
However, the Mk2.5 electric manual shows a transistor in series with the field coil mounted ONBOARD, but the transistor base is fed to the ECU and presumably through another transistor that decides how much variation the onboard base transistor is allowed to flow to negative. therefore varying the field strength and final volt/current output.
I would assume therefore that Mk1 alternators have no field output connection, - so regulation is contained onboard the alternator.I only have a Grainger/Shoemark manual, so a bit sparse on electrical circuits. Mk2 and 2.5’s would seem to have an additional two pin/two wire connection to the ECU, which is the remote regulation by the ECU. As the current flow in that circuit is relatively small (6-8 volts according to the Mk2 manual when engine is running) then neither current or heat is a problem.
My logic says a Mk2/2.5 alternator will not work on a Mk1, but whether a Mk1 alternator would work on a Mk2/2.5 is open to question, as it would seem to be self regulating. What we do not (as usual) is what’s inside the empty box shown as the ECU, so if a lack of field coil voltage will make a difference to how the Mk2/2.5 Runs is the unanswered question. Suck it and see seems the only way to check. Rhino’s second post above provides half an answer it would appear - (It doesn’t work )
To understand what I said, you need to understand how transistors work.
The alternators are becoming more powerful and the built-in control systems more sophisticated. Remote sensing of the battery voltage is common (the thin positive lead). On some the heavy positive lead from alternator to battery is a carefully calibrated resistor to allow the control circuit to limit the charging current, easily done when it is measuring the voltages at both ends of the lead. Some systems can apply adjustments to maximum charging voltage according to the ambient air temperature.
If the alternator does not have an additional thin wire, then it will be fully self contained. If it has one or more additional thin wires for remote sensing or control then all bets are off!
My 1977 Mk1 Cavalier boiled the battery at only four years old, because while it had a remote battery voltage sense lead, the relevant spade terminal on the Bosch alternator had rusted and gone open circuit. This meant I got the car very cheap at less than half the bottom book price for a high mileage car. I welded in a new battery tray, and repaired the rusted spade terminal by cleaning it back to metal with emery and then applying a generous tinning of solder, and that alternator still worked fifteen years later when I scrapped the rust-free car with 9 months MOT (nobody wanted to buy it!).
I reckon the regulator process must generate some heat because they are all fitted with decent sized heat sinks. This was the giveaway on the ECU - no sizeable heat sink.
They have managed to incorporate ecu control using the same number of wires as the earlier ecu. All have the standard large guage wire attached to the main pole and a separate insulated connector plugin with 2 wires. I have seen some aftermarket replacement alternators with an extra spade on the back but not used on the MX5.
This indicates to me that the alternator regulator is the ‘grunt’ totally controlled by the ecu.
Bizarre results with diode rectifier test too. The four MK2 alternators I have recorded around 500 whereas the twoMK1 1.8 Mitubishis showed a figure or around 1000.
That is very sad to hear Richard - used to be a very common car back in the day along with the Chevette - how many are on the road now?
Given the mid life crisis rise in prices of these cars at the moment I guess this would be worth good money and likely be sold to someone who would look after it rather than for cheap transport.
Strangle enough one of my customers who is rallying his MX5 as we speak, also races Vauxhall Chevettes. The interest in alternator technology has come about because his MK1 is only charging at 13.2 volts with a serious parasitic drain. This, it turns out, is a classic diode problem where one of the six rectifier bridge diodes has gone down. I supplied him with a beautiful clean alternator but charging at around 15 volts, pointing at a regulator fault. To make sure the replacement I sent out was working properly I fitted it to my MK1 and tested before sending out. Hoping to persuade him to allow me to collect his original alternator as well as my faulty one. It seems the rectifier is a lot more difficult to fit and correct one not available whereas I could repair my one with his regulator. Hopefully he will see the sense in this.
By 500 I assume you mean 500mV as forward drop when one diode is conducting. The 1000 will be two diode junctions in series.
How are you measuring the forward voltage drop? Externally from + to -? Or from the winding through the stack to - or to +?
There are two standard configurations for the high current circuit. And then either might have another set of three to an extra + for the internal control circuit etc, when in theory the regulator is guaranteed not to flatten the battery if the engine is not running.
Star, with centre point grounded and three high power diodes all to +. This single diode forward voltage will give the 500mV reading on an external measurement.
Delta, six high power diodes are needed, with a pair from each apex of the floating delta, three diodes to - and three diodes to +. The forward voltage of the pairs of diodes will give the 1000mV external reading.
Those voltages are for standard high current silicon diodes, proven reliable technology. I don’t know if any of the latest Schottky diodes have a high enough current rating and more importantly a low enough reverse leakage current for this application, certainly not the case twenty years ago.
The brand new Lucas alternator I put on my Kent engine back in the early 1970s had a nine diode stack, with the extra set of three for the second + internally connected to power the regulator and field winding. On that alternator however it did develop a leak after a while, which turned out to be the silicone potting missing a bit on one diode chip and the carbon dust from the brushes was forming a short. After I cleaned it and re-potted the diode with some bath sealer it lasted well until the shoddy (ie normal Lucas) unsealed ball race began to fail. New double sealed (ZZ) ball race and it lasted until the car died from the red disease.
A good book covering general automotive electrics and (most of the time) easy enough to help most people to understand them is the early Haynes one by Tony Tranter, and it gives an excellent explanation of how generic alternators work with some specific examples as well.
My well-worn copy is a bit out of date now (published in 1990) but at least I knew it covered what I needed on the old cars and it was written when Haynes did things properly.
There are several much more modern (and expensive) books if one searches on Az, for example the Denton textbook which is 700 pages of massive comprehensive overkill with everything we ever wanted to know and so much more, but can anyone understand it?
Sorry gerryn I said that there was no active regulation in the ECU as wrongly I suspected it was some sort of chopper used to reduce voltage and I said that would not happen in the ECU as it was not sturdy enough to take the heat and was covered by a carpet therefore in the wrong place to do shed heat.
I supposed the ECU would remote control the regulation in the actual alternator and that would cause no heat of any real amount to be generated in the alternator.
You have just spend a pile of words agreeing with me apart from there being no heavy duty heat generated in the process of voltage regulation.
Eddie - O/K - I wrongly interpreted what you were saying - but one paragraph is a whole pile of words? >
“However, the Mk2.5 electric manual shows a transistor in series with the field coil mounted ONBOARD, but the transistor base is fed to the ECU and presumably through another transistor that decides how much variation the onboard base transistor is allowed to flow to negative. therefore varying the field strength and final volt/current output.”
That was a rough interpretation of what’s inside the empty box shown as the ECU, obviously there’s voltage comparison involved to drive the ECU output back to the Alternator.
Rest of that post was comment, one way or another.
Last comment (unrelated note for Rhino) bear in mind that an NBFL alternator has a different alternator swivel adjustment point mount to either an NA or NB - check MX5 parts - as we found out recently when trying to replace the alternator belt.
I’ve just been having a read about the alternators in my old book, and as well as the pesky remote sensors it reminded me that for ‘Machine control’ there is almost always a wire from the ignition light and switch.
The battery feeds it through the ignition switch and the ignition light, and the wire goes to the top of the field winding and the extra three diodes. It works as a priming circuit to kick start the alternator field if there is not enough remnant magnetism in the core.
If the light stays on with engine running it is because there is no internal high current supply (often up to 3amps needed) to the field winding and therefore no charge. Check rectifier.
If it flickers check the brushes, or the wiring, or rectifier.
If the battery is ever connected the wrong way round, oops, then it is likely all the alternator semiconductors are toast.
The Alternator for the Mk1 cars has B, S, L, for B (Battery via bolt, thick white), S the Sense from battery (white/green), L the ignition warning Light (white/black).
If the alternator has the two small pins (L, S), then both need to be connected. It has internal control but with remote battery sensing.
If it only has one (L) then the ignition light is the one that needs to be connected. It has internal Machine Control.
The Alternator for the Mk2, Mk2.5 cars has B, P, D, where B is White as before, but P (Phase tells PCM how fast the alternator is turning) and D (the control wire, PCM tells Alternator how much current is needed - ie more volts ask for more current) go to the PCM before seeing the Ignition light.
PCM is controlling the alternator’s internal power management unit while monitoring its performance, and so this alternator has a different internal control unit to that on the Mk1.
Thanks for your input. The later post clarifies technically what we had already concluded. MK2 and MK1 alternators are not compatible and I do not need to do any field tests to prove this:-)
My diode test was very simple as picked up of utube - god bless the internet.
Diode tests on a multi metre show Mv output so yes correct.
Black lead to large pole and red to alternator case to get Mv reading. Reverse polarity of metre leads should show 1. Anything other than 1 would indicate diode flowing two ways and parasitic drain and lower charge voltage. As the drain is likely to be 2 amps or more, the battery draining overnight would probably be a clue.
utube expect a reading of around 500Mv. I am wondering if the stator windings on the alternators are causing this difference as there are two standards?
To add to this I have an immaculate MK2 recon alternator that apparently isn’t charging, Strangly the components - rectifier and regulator look MK1 Mitsubishi style.
Diode test - wait for it 304Mv
Nothing written on rectifier but regulator looks like this one…
I have stripped this unit and it is immaculate - windings still paint fresh - any ideas Richard, rectifier diode test looks abnormally low?
Going by the pictures on the ad, that unit on ebay is the later type for BPD operation with ECU, which looks right.
It is important to try and test the individual diodes in the rectifier stack disconnected from the stator and control box. If one diode is different to the others in its triad (ie common anode or common cathode) then the stack is likely to be scrap. The two high current stacks should have the same rated diodes, the field stack might well use a lesser diode.
If the diodes are Schottky the forward voltage at test meter currents will be about 120mV-250mV per diode, or 240mV-500mV for the complete stack. At the full 50Amp (or more) output the forward voltage is likely to be at least double this, but still less than a silicon stack at the same current.
The stator winding resistance should be so low you cannot measure it with a multimeter; the meter’s test leads will be a lot higher in resistance. Remember the alternator is going to be producing more than 50Amps, so a mere tenth of an ohm will drop five volts and dissipate 250watts - meltdown. Any loose bolts or poor soldering in the assembly are also likely to prevent effective working.
Check you have continuity through the field winding and the brushes and that the slip rings are not damaged or shorted by contamination such as swarf. (The last heater fan I repaired had a dry joint where the flexy braid of one commutator brush was soldered to the circuit board.)
The reverse conduction of the rectifier should be so low you should not be able to measure even a milliamp from a 12V battery, and the reverse resistance across B and case as measured with the test-meter (internal 9V battery) should be more than 100 Kilohm with Schottky diodes and more than 10 Megohm with silicon diodes.
I notice that the typical replacement stacks being offered for assorted alternators in Mazdas often double up on the quantity of diodes, so there are two pairs sharing the current for each leg of the three-phase winding making 12 high power diodes, typical diodes being BN50N-P and BN50N-N.
I would expect the various types of modern control box casing from a given manufacturer for the same current to be almost the same apart from the one/two/three pin connector and the contact labelling. Some now use a single-pin bidirectional data bus others a ring-main bus called LIN supporting a whole load of devices in the car as well as canbus. The circuits hidden inside a similar shape box are likely to be essentially the same apart from a couple of small transistors and resistors, and with a modern type I expect it could easily be the same integrated circuit chip and circuit board to control both BSL and BPD but with alternative option pins chosen/populated for the appropriate functions.
I assume you looked at the diagnostic suggestions in the Mk2/2.5 manuals for Charging System? With specific attention to see if the PCM is receiving the 3-8V on P and varying the D signal to meet the load change?
GENERATOR INSPECTION
GENERATOR WARNING LIGHT 1. Verify that the battery is fully charged. …Charge if necessary. 2. Verify that the drive belt deflection/tension is within the specification. (See DRIVE BELT INSPECTION .) …Adjust if necessary. 3. Turn the ignition switch on and verify that the generator warning light comes on. …If the warning light does not illuminate, inspect the harness from ignition switch to generator warning light and from generator warning light to 3U terminal of PCM. If the generator warning light and harnesses are normal, replace the PCM. 4. Confirm that the generator warning light goes off after starting the engine. …If the generator warning light does not go off, inspect the on-board diagnostic system service code. (See ENGINE CONTROL SYSTEM OPERATION INSPECTION [BP, BP WITH TC] .)
GENERATOR
Voltage
1. Verify that the battery is fully charged. … Charge if necessary. 2. Verify that the drive belt deflection/tension is within the specification. (See DRIVE BELT INSPECTION .) …Adjust if necessary. 3. Turn off all electrical loads. 4. Turn the ignition switch to START and verify that the generator turns smoothly without any noise while the engine is running. 5. Measure the voltage at the terminals shown in the table. …If not as specified, disassemble and inspect the generator.
Terminal Ignition switch ON (V) Idle (V) [20 °C {68°F}] B B+ 13-15 P Below 1 Approx.3-8 D Approx.0 (*)
(*) Turn the following electrical loads on and verify that the voltage reading increases.