I recently came by a 1500 watt UPS that run on 48VDC. I would like to install this in a School bus gone RV. Plan is to convert a alternator to 48 VDC and drive it from this if I can find some good info on how to convert the alternator.. Any help would be appreciated.
Most alternators are capable of producing 55-65 amps. Some more modern vehicles have alternators rated up to about 120 amps. Some pre-1985 cars, on the other hand, have alternators only rated for 35 amps. None of these will generate enough to power a 1500 W UPS on full load. Modifying an alternator is certainly possible but usually takes it away from optimal conditions and reduces its power output. It is a pretty skilled job though and an engine compartment is a pretty hostile place for modified electrics. How to do it would depend on the type and model of alternator.
Have you considered selling the UPS and buying invertor(s) that run off 12V? They are now very cheap - I have just bought some 300W ones for under 20GBP each. Rather than wire a friend's boat with "mains", I wired it with 12V and put an invertor in each cabin - it worked out a lot cheaper and means that there isn't one big invertor to start up and run inefficiently when one tiny load is switched on.
If you really want to progress the alternator mads, can you supply some more details of the one you wish to modify?
It probably isn't worth the effort. A 1500W UPS that runs on 12 V will be far less expensive and far less trouble.
However... Use two 24 VDC truck batteries. Have your vehicle rigged up with two (30 Amp) 24 volt alternators and wire them in series.
That said, you still have some adjustment problems. A 48V UPS is almost certainly meant to be used in a telephone office. It will expect a normal DC voltage of 52 volts and should operate down to as low as 42 V (at which point you should have a "low voltage cutout" to protect the battery). On the high end it would expect to see as much as 56 volts, but never over 58 V.
That differs from an automobile/truck arrangement where the typical voltage on a 12 volt system runs from 13.8 to 14.5V, so a 48V system would see 55 volts normally, and frequently up to
58V. So it would operating right at the upper end of the "normal" range it was designed for. That is not a real problem, but you do want to be aware of it and be positive that it doesn't ever get too far out of specs towards the high end.Note that the alternators, in series, would provide 55 volts and if the UPS pulls 30 amps that would be 1650 watts.
Doesn't some military and construction equipment run on 48 VDC? If so, maybe a salvage yard would be a good place to look if you want to save some work.
Dean
In the 1970's there were adapters that converted alternators that used external voltage regulators into 120 VDC sources for running power tools that would operate from DC. That indicates the basic field in the older alternators could be overdriven enough to produce much higher voltages. Should be possible with newer alternators by removing the voltage regulator assembly and providing the necessary field voltage control to produce the desired output voltage. May overheat if used for long periods at the higher output. I have never tried it.
Bill Kaszeta Photovoltaic Resources Int'l Tempe Arizona USA snipped-for-privacy@pvri-removethis.biz
first let me make a guess and tell me if i got it wrong. you acquired a smallish inverter, perhaps a rack mount unit that was intended to back up a computer server(s) for perhaps 10 to 15 min depending on load. it uses four
12 volt gel cells that are wired in series.perhaps you intend to outboard some bigger batteries like maybe eight 6 volt golf cart batteries to run the inverter for a few hours. maybe you are just looking for a way to keep it running while the bus engine is running.
one possible problem it that the backup UPS units generally don't handle continuous duty very well. after about an hour they have a tendency to go into thermal shut down. (of course i don't speak for all models... just an observation of the ones i have encountered)
you got some excellent advice from the other posters but i think some additional input is required.
what is the make and model of the UPS? what specifications are listed for it? what is your expected load in watts? in what manner will this be used? while driving down the road? while parked camping? both?
one word of caution. i have a 200 W inverter by Tripp Lite. i sometimes use it to power test equipment in mobile applications. on occasions i step out of the car with the inverter running. if it is raining or the ground is wet it "bites" me. i am not sure why this is maybe capacitance to ground?
i would suggest if you proceed with the project to install GFI breakers or outlets for protection.
dean from great barr??
Nope.
On my daughters computer but this is Jimmie, UPS puts out about 3 times as much power as I will draw from it. It has sine wave output which i need. I know of it running on battery for at least 4 hours with no problems. Pretty sure this is the type where a charger converts the mains input to dc and the batteries float on the DC. Basically it is running all the time. Will get the brand name next time I go by the shop as I cant remember it now. Also have other needs for a 48VDC power supply on my bus. This thing uses 8 100amp hr 12 v batteries in series paralell. When the equipment was removed from sevice I got 4 of them
NO. 8 100 amp hr deep cycle batteries in series paralell
While the bus is running mostly.,
No this should run from now to hell freezes over as long as it has 48 volts. Runs continuosly from charger batteries float.
a search for "alternator 48 volt" turns up a number of sites relating to wind power generators. here's an 800 W one
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.