Magneti Marelli alternator 3 phase rectifier ROD1B 0206 maximum voltage ratings? - Page 1
Forum section: electronics / projects

author: eneuro
author_rank: Super Contributor
timestamp: June 19, 2014, 01:04:07 pm
content: Hello,I've Magneti Marelli alternator made in Italy not ChinaI've removed internal voltage regulator while I need to switch it on at lower RPM speeds, but I left oryginal 3 phase rectifier while it has nice design and is quite well cooled when alternator is running.However, I do not can find any specs about this alternator and its 3 phase rectifier maximum voltage ratings-it is not 1000Vmax I guess?Rectifier has such code:ROD1B(orROD18it is not clear to see, but for sure notROD16)Magneti Marelli 0206.Maybe someone know what its maximum voltage ratings are, and hopefully maybe it is possible to find any datasheet of this alternator?Regards.

author: Neverther
author_rank: Regular Contributor
timestamp: June 19, 2014, 03:51:01 pm
content: RDD16? You got that from a Fiat Uno?I've replaced diodes on Marelli A127IR rectifier and I remember them either being 100V or 300V, so realistically safe up to 60V output?This rectifier is a lot smaller so I cannot say for sure. Depends what they threw in there, different manufactures might have diodes with different rating (whatever was cheapest/in stock and within minimum spec).Just burn one, rectifier bridges arent that expensiveThe stator insulation isn't designed to take on too much voltage and that alternator is rather weak anyway (35/25A).Vreg tries to keep the voltage regardless of the RPM, it not working means the alternator doesnt have enough output to drive the stator coil (usually the current comes from separate diode trough the stator to the pass transistor in Vreg, this way it wont drain battery or fry sliprings if the alternator doesnt spin, the exciter wire usually goes trough the lamp on dash so it is current limited).

author: SeanB
author_rank: Super Contributor
timestamp: June 19, 2014, 04:47:41 pm
content: A lot of those diode bridges have transient supression by having diodes with a breakdown voltage of around 30V or so for a 12V unit, so that they limit voltage if the battery is disconnected or goes open circuit to a level that will not cause arcing in the windings. Typically they will deliver 28V for a 12V unit being grossly overdriven with a low load, but can be anything between 30-50V open circuit. If you want it to run at full output at lower engine RPM you need to turn the input shaft faster, either by having a smaller diameter pulley on the alternator or a bigger diameter pulley driving it. It then will give useful charging at low RPM, but you then are limiting the max RPM allowable on the engine, which can blow the alternator apart. Regulator makes no difference, it only controls maximum voltage allowed on the battery feed, not the actual charge current, which depends on battery float voltage ( difference on SOC from flat to the expected cut off at 14.4 volts on the regulator) and input shaft RPM only.

author: eneuro
author_rank: Super Contributor
timestamp: June 19, 2014, 06:53:38 pm
content: Quote from: Neverther on June 19, 2014, 03:51:01 pmIt looks like RDD16 on other photo before it got his second lifeI have 2A fuse on rotor coil which is powered by high frequency PWM from external battery 12V.What could be safe maximum current for this rotor which creates magnetic field inside? As I remember its resistance was about 4 Ohm, so when powered from 12V battery 3Amax could flow without any additional resistor or I missed something?Quote from: SeanB on June 19, 2014, 04:47:41 pmThere is no oryginal voltage regulator no more while hacked and disabled built inAlso removed this useless one diode from rectifier, so no I have rotor coil wires, 3 phase windings and 3 phase rectifier with external regulatorUpdate: There is also this oryginal capacitor 2.2uF from rectified B+ to B-.I've made custom alternator controller with analog Hall sensor SS495A based current sensing circuit and microcontroler (ATTiny85) with output voltage measurement and by adjusting PWM I can drive rotor coil regardless of its RPM and the limit is its maximum current.It is diffcult to see gauge of this rotor coil, so decided put there 2A fuse for the moment.Of course this alternator is not used in car no moreI can limit its output current and output power, so I can keep desired RPM regarless how low resistance is connected to its output, but it would be nice to have its datascheet like this another oneA93/90A -13.5V 90A:http://www.magnetimarelli.com/sites/default/files/SF_A93_90A_rev9.0_p.pdfwhere at typical performance graph we can see how much power we can get from it based on its RPM speed eg. 30A @ 3000 RPM.I do not need more than 500 W (0.5kW) rush power but it would be nice to push to the limits its rotor current and maybe even add another custom cooler to be able to feed it with higher currentWhen bigger current is aplied more power is needed to turn rotor or keep his RPM, there is stronger magnetic field inside, so I should get higher current at voltage maybe too low for direct battery charging, but good for step-up boost switching regulator ICs and boost switching controller ICs

author: Neverther
author_rank: Regular Contributor
timestamp: June 20, 2014, 07:21:48 pm
content: Quote from: eneuro on June 19, 2014, 06:53:38 pmThat is propably the diode driving the coil, or vreg, depends on the alternator design.I do think that is 25/35A MAX unit so your 500W might be a bit out of range, you'd need about 20v out of ot to reach the wattage.And you need the alternator spinning fast enough just to cool it.The rotor coil is usually rated for 14.7V (minus pass transistor loss) so it can take a bit more, say 20%?Monitor the temperature, if you run it on full load, it will heat up and die. There is reason cars have alternator placed behind front bumper or have air ducts into them.The original vregs are just simple comparators with voltage reference, output is connected to the pass transistor. The coils are large enough to act slow so it basic system like that is enough.Alternators just produce current, the load connected to it determines how much output current is needed for the desired voltage be across the load.Vreg monitors this voltage and controls the rotor current, which in turn controls the output current.

author: eneuro
author_rank: Super Contributor
timestamp: June 20, 2014, 09:52:57 pm
content: Quote from: Neverther on June 20, 2014, 07:21:48 pmIf I had circuit diagram of this alternator voltage regulator it could be easier, but I've found another one:I've removed those isolation diodes (they were close to rectifier diodes), but it looks like realy this rotor coil could be driven directly between 14V-15V as you rated itI'm unsure if I removed this DF diode while I did not noticed it inside this voltage regulator and I have another one fast Shotky in my controller while it is needed to avoid spikes when this high inductance rotor coil is switched off by regulator transistor on the bottom.I have mosfets 2xIRFZ44N with RDSON 0.017 Ohm each, so this oryginal transistor is bypassed too I guess, while It worked so far without problems.However, I think I have to open voltage regulator case again and ensure that I have no connections to this builtin transistor.It looks like I have similar voltage regulator circuit, while now alternator nice builds up output voltage even at low RPM speed while this rotor coil is powered from another small 12V battery, so there is no problem that alternator output voltage will be even higher than 20V while rotor coil is not powered directly from its output like in oryginal voltage regulator circuit and maximum rectifier voltage, its isolation, maximum alternator RPM is now a limit for higher voltages at low load.I think, I will set maximum output voltage limit in my controller to 48V and 30A current, connect its rectifier output with >100V diode to ensure if rectifier fails external load will be safe powered by positive voltage and I will try to reach those 48V under load up to 5A at highest RPM possible and see what happends

author: eneuro
author_rank: Super Contributor
timestamp: July 15, 2014, 03:55:49 pm
content: Finally limited alternator rotor curent to 2A which @ 6V and about 3.6 Ohm total impedance @ 10kHz PWM limits power loses in rotor to about 10W-15W, but it is easy to set this maximum rotor current higher while it is step down buck converter from 10.5V+ battery connected directly to alternator output.Output power Hall current sensor based on SS495A calibrated and when loaded with 10A it give nice 200mV difference from 2.03V to 2.230V, so it is about +/-20mV per +/-1A (when current flows to alternator this current sensor output goes down)Implemented optical encoder into this alternatror controll MCU software (AVR ATTINY85) DIP8 and it performs quite well @ 8MHz internal oscilatorIt is easy spin it up, while rotor current is a function of its RPM speed designed to limit maximum current @ given rotor speed-it does not require a huge input power when low resistance load is connectedI think, it will be good idea limit output alternator current to 20A-25A and it looks like another improved alternator controller for HPV vehicle is ready for test runwith other subsystems