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
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
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.
On 10/31/04 1:03 PM, in article
bGahd.12995$ email@example.com, "Jimmie"
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
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.
Photovoltaic Resources Int'l
Tempe Arizona USA
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
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.
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.