WTB: 36 volt alternator

Go to your nearest auto junkyard. They have many, and cheap!

-Dennis

thanks but i need a 36 volt unit. sam

I'm not positive, but aren't most alternaters

48vdc? Putting several diodes in series would drop the voltage down to 36v. Again, I'm not sure about the 48v thing. Disregard, if I'm all wet!

-Dennis

Assuming that you are attempting to charge three 12V batteries connected in series, you could, during charging, connect them in parallel (there two are different school of thoughs about this, some advise the use of isolation diodes to prevent circulating currents, but if the batteries have the same capacity and are of the same age, you could avoid the diodes), then after charging, reconnect them back to series using a common selector properly wired. If this is not possible you could explore the possibility to rewind the 12V alternator or ...... buy a 36V alternator. Rudy

Correct description seems to be 42 volt alternator (since to top off

36 volt batteries, you need to charge them at 42 volts just as 14 volt alternators charge 12 volt batteries). I have not found any commercially available alternator on the web - but maybe I did not search enough. Does anyone make such alternator yet (other than at car makers' future concept car design & test labs where a prototype 42 volt alternators might be under test by now).

There is a professor at MIT who has been working on 42 volt alternator for a few years now. Check out the article below.

It WOULD be interesting to know if 42V alternator can be purchased more or less "off the shelf".

isn't the 36 volt alternator what i was searching for? i use the charging as a hybrid over batteries. i can't parallel them while riding. thanks any way sammm

no, they really aren't . in fact some are wound wye connected stators and some are delta (all are 3 phase) but thanks for the thoughts. sammmm

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Here is one idea. You might be able to design & build a voltage tripler using 6 FET's (say 100V, 100A types) and connect them to 3 batteries connected in series. Each battery gets a pair of FET's and driver which turns on both FET's at once. Then 3 such driver/FET can be turned on sequentially every 20 ms. Thus each battery will be charged for 20 ms every 60 ms (pulse charged with 33.3% duty cycle). Battery life may be sacrificed a little bit, but for quick 42 VDC battery charger using "off the shelf" 14V, 60 amp alternator, this should do the trick. Of course, the effective charging rate will be 42V, 20 amps, so it will take 3 times longer to charge 3 series connected batteries fully as it would one battery, but that's another little sacrifice you will have to make.

I read in one of the articles that one 42V alternator being developed was going to produce something like 5000 watts (42V, 120A). With that much power from an alternator, 42V cars could be packed with tons of creature comfort features (heated seats for all passenagers with AC outlets for each passenger -if are in a hurry, you could dry your hair with 1800 watt hair dryer in your car while toasting on a 300 watt heated seat while outside is -30 degrees)!

Some railway equipment (locomotives, rail cranes, switchers, even those little Trackmobile shunters) run on 32 or 36 volt electrical systems - perhaps contacting your local railway maintenance shop might give you a lead on 36-volt electrical items.

Bill

You may be able to get 36 (42) volts out of a junkyard alternator by simply overdriving the field, and possibly replacing the rectifiers with higher voltage units. Derate the alternator's current to 1/3 its previous value so as not to saturate magnetics (or maybe break something mechanical!)

A second option is to bypass the alternator's rectifiers completely, so it produces AC, and either supply a transformer (3 transformers, 3 phases) or feed a voltage tripler system (3 of them, again because of

3 phases). Any transformers will have to handle whatever frequency swings whatever is driving the alternator is capable of producing.

A voltage tripler (half wave) can be made from 3 rectifiers and 3 capacitors (total 9 each). This is what I would do.

Subaru uses a combo 2 Kwatt starter & 3 Kwatt alternator in its new concept car. Since it was shown in 2001 auto show, maybe it is in production in Japan and parts are availble more or less "off the shelf" in Japan?

Not having tried this, my objection to this route is mostly theoretical. I suspect, though, that a practical automotive alternator is designed so that the flux is already pretty close to saturation anyway - you're unlikely to get enough field current through the rotor to increase flux by nearly 3-fold.

Of course since the output voltage is a function of both flux and

*speed*, perhaps just running a regular 12 V alternator at higher speed is enough to get 36 volts out of it. Its not like you care what frequency is coming out, since it's just going to be rectified anyway. Since the auto alternator has to stay in one piece for a wide range of engine speeds, mechanically it should stay together. Brush life might be a problem.

Bill

The standard car alternator puts out ~14V with the engine at idle and nearly full field. But car engines can go from 600 RPM at idle to over 3600 RPM (factor of 6 easily). The alternator of course runs somewhat faster based on the pully ratios. At these higher speeds, the voltage would be excessive if it were not for the alternator.

So, perhaps upgrade the rectifiers for the higher voltage, run at higher speeds, and control the field with an external regulator. Be sure to limit the field current to the same as the original value to avoid overheating/saturation.

But you may not be able to get full current out of the alternator. The internal impedance is a function of the internal frequency and will act to increase the internal voltage drop with load.

daestrom

interesting theory but i'm getting easily 44 volts out of the 24 volt truck unit with 14 volts on the rotor. the speed is governed by the briggs and stratton engine governor. the saturation is no problem but i find that the stator (with the windings disconnected) has a lot of heating from eddy current losses when the rotor is excited at high levels. the rotor is normally run as high as 28.2 volts with the normal 24 volt regulator in place. this is for the low speed charging capabilities. there's obvilously a lot of iron and copper in the rotor to allow this speed range to work in normal use. my main reason for asking about a 36 volt alternator was to not need to screw around with developing a unit if one was really available off-the-shelf. i i've done the research on both 12 volt and 24 volt basic alternators and both are working well. thanks, fellas. sam

Searching in the wrong camp....

The normal car alternator doesn't have 14 volts on the rotor very often. That is the function of the regulator. It regulates the current through the rotor circuit to maintain the desired voltage at the output. Connect directly to a battery and you have a fixed field current.

Then the only way to regulate the voltage would be to vary the *other* parameter, speed of the alternator.

Well, for a truck unit, that would be normal. 12V car alternators put out about 14V when running on the regulator, so I would expect a 24V system to put out about 28V when on the regulator.

daestrom

thanks for the tip. sam