A few days ago I started a thread titled "superoversized alternators"
on m.s. and a.h.r. My question was how to use an alternator from my
pickup truck as al alternative source of emergency power. I do have a
diesel generator but it is broken and I need to spend time on it. I
suspect that I am missing something trivial with the generator as it
looks great and is military surplus bought directly from military.
My primary need for power during power outages would be to supply
power to the furnace blower (nat gas), fridges, and some house
lighting and maybe TV/Radi.
My solution is as follows: I have a Ferrups FE series UPS. This is a
1.4 KVA model that has a regular gel cell lead acid 12 volt battery as
the power storage. By the way, I found that Ferrups UPS on a street,
someone simply took it out to the curb. (!)
I would keep that ferrups plugged in and charged. I will also connect
3 gauge stranded wire to the battery posts of the UPS so that the wire
can be connected to an outside 12vdc power source. If power goes out,
I would connect the furnace to the UPS by means of extension cords
(some rewiring of furance would be needed to accommodate it
safely). Then to supply more power than is stored in the 12v battery
inside the UPS, I would start my pickup, run it at idle speed, and
connect the battery posts in the truck to the 3 gauge wires I
connected to the UPS battery (see above) with a jumper cable.
Advantages of this setup:
1) Can accommodate surges of power without putting extra load on the
alternator, because the UPS itself has a reserve of power in the
2) I do not need to buy a separate large capacity inverter, will be
using what I already have
3) For brief outages, all I would need is running extension cords to a
few freestanding lights. and the furnace.
I am aware that devising means to switch the furnace to alternate
source of power, without buying a transfer switch, is tricky. I will
try to do something that is safe and to the code. My current
inclination is to supply the furnace with a 1 foot cord that would
plug into a regular outlet, or the UPS or generator's extension cord.
You can't safely hook together lead acid batteries in different
states of charge.
This can cause very large currents to flow.
This isn't trivial to fix, unfortunately.
Simple resistance of the cables helps, but it's not 100%, unless you'r
dropping a lot of voltage in the cables.
The much safer way is to install a changeover switch.
This would switch between external and internal battery.
This does need a large switch, capable of safely handling 12V at around
http://inquisitor.i.am/ | mailto: firstname.lastname@example.org | Ian Stirling.
What about jump starting cars then?
Anyway, it is not a bad idea to change over from the internal battery
to external, and, I believe, can be done quite easily and safely. I am
not 100% convinced that it is completely necessary because people do
jump start cars after all. However if I get reasonable doubt as to
whether a direct coinnection is safe, I may do a changeover.
Something for you to consider. While I am not familiar with your
particular make and model of UPS I have used several types.
I have seen older ones where the protected equipment continuously runs
off of square wave or modified square wave inverters. These run the
input power (from the grid) to keep the battery charged. This type
does not do any switching, because your equipment that is plugged into
the UPS is always running off the battery.
The later ones I have used run directly off of grid power until they
get either a spike or a dip in power and then switch to the UPS
inverter power. The ones I have used were sine wave inverters. The
difference in quality of this type is the speed in which they can
switch. The good ones are very fast. One thing to note is that (at
least on the ones I have used) if it is not on and running when the
power goes off you can not turn it on after the fact and get any
output power. It has to be plugged in and running when the power goes
off to switch and produce off grid power. The second and most
important thing for your application is these are not continuous duty
inverters like the ones designed for off grid power systems. They are
generally designed to keep sensitive electronic equipment running for
about 15 minutes. This is so if it is only a blip or short outage you
can continue to work uninterrupted or if the power does not come back
in a few minutes you can shut down gracefully and not crash and loose
data. These things get very hot. The battery they come with is
designed to be big enough to run the UPS for as long as the internal
electronics. If you give it more battery power from an external source
you may be exceeding the capabilities of the thing to get rid of the
heat it generates. I know of one guy who used his computer UPS in this
way during a blackout. The fancy phone system in the office went down
and customers could not get through. Not wanting to loose business. He
unplugs computer from UPS and runs extension cord to room with the
phone exchange equipment. Works great for awhile. Then battery runs
low so he takes battery out of his truck and ties it in and it's
working great again. That is for another 15 minutes, until he totally
melted the electronics in the UPS. A puff of smoke and then a bad
burnt electronics smell. He exceeded the design ability of the unit to
Thanks. I will check tonight if my UPS can be powered in absence of AC
power. It does produce sine wave power. It also has a 0ms transfer time.
Ferrups are generally considered to be the best of breed of UPSes,
built like tanks. This is not a "consumer grade" product. They are
also offered with "extended battery modules", which strongly suggests
to me that they are designed to run off battery power continuously.
They also have a 150% surge capacity even when running on the
``The Powerware FERRUPS UPS deliver unmatched reliability in
configurable power protection for computers and telecommunications
equipment. Patented Ferro resonant technology delivers "bulletproof"
power protection and is ideal for banking and security systems,
manufacturing process control, servers, and telecommunications
Thanks, I know what you mean. Hard to build cheap stuff to sell to
uninformed customers and that also works very well. Ferrups are
generally fairly expensive but they have a lof of features. That one
surely has a built in fan, I saw it when I took the UPS apart.
One last concern that I have is that when my truck engine is running,
the voltage reads as 14 volts, not 12.4 or so as it would be from just
a battery. Can it damage the inverter?
For some loads they are equivalent.
Heaters, and lightbulbs, for example.
The problem arises when you try to connect equipment that has a power-factor
of other than one.
With a 110V mains, the voltage varies smoothly between -155V and 155V, back
and forth 120 times per second.
The power factor is a measure of how "in step" voltage is with current.
Some loads like induction motors, some sorts of power supplies, ...
have the current out of step with the voltage, which means that for a
given current (the guts of the UPS tend to be rated by output current) the
wattage is less.
For non sine-wave outputs, these sorts of load are even worse.
The music power is pretty much an intentional lie.
The VA rating of the UPS is an indication of it's true capacity, and can
be sized in exactly the same way as (for example) breakers.
A 110V 20A breaker will run a 2200W or so load with a power factor of one,
but a much smaller load with a power factor of 0.5.
It's the same as the UPS.
http://inquisitor.i.am/ | mailto: email@example.com | Ian Stirling.
They do it this way partly for marketing and partly because when something
is stated at so many VA then the user/installer can figure out what the
operating current will be based on the local input voltage. The input
voltage can vary depending on where you install the unit. So on a 1400 VA
unit if the input voltage is 120 V the AC INPUT current is 11.6 Amp. If the
AC input is 115 V then the current used is 12.2 Amps etc. In the past the
VA was used primarily on motors and compressors and such. If not VA then the
manufacture would have to put on a huge label with several lines of text: If
110 V then x Amps.. if 115 V then y Amps.. if...etc.... If they use a VA
rating then just a few charters will tell all. Now for the UPS it is not
really necessary to use the VA, but it gives you a bigger number to look at
for marketing or advertising . Just like the vacuum cleaners manufactures
that advertise a 12.5 Amp Max... It has nothing to do with the efficiency of
the vacuum cleaner itself. How much power are the head lights cornering
lights, turn signals..... etc use?
For the UPS you must subtract the current used by the electronics, charging
circuit etc. to come up with the usable output current/power rating. A label
on the back should say. (The 1400 VA UPS should give about 900 to 1000
Finally for the OP the charging circuits for the sealed lead acid batteries
are different than for the relatively crude charging circuit used for
automobile batteries. If you didn't have a isolation switch then when the AC
power is restored, the UPS will attempt to charge the auto battery which may
demand more current than the UPS can give. (but I guess you could leave the
UPS unplugged from the AC). If the car engine is running the UPS might not
like the alternator output?
One more very important issue.
What DC voltage does the UPS really use 12V or 24V or more? Pull the
batteries in the UPS and verify how they are wired. Or use a voltmeter. Do
not rely on the voltage label on an individual battery. It is probably using
from 2 to 4 batteries in 24 volt series/parallel arraignment. You would need
to use 2 or more car batteries to provide that voltage.
Sorry I was thinking more resistive loads. But I do believe that they use
that VA term to confuse people into thinking that they are getting more than
An APC brand UPS that I have used is rated at 1400VA and has a prominent
1400 silk-screened on the front of the unit which is also the model number.
However the max output is 950W at 120V. Why not show me 950 on the front as
that is much closer to the real output? I think that they just chose VA
because it looks bigger. One time our SA complained that the servers were
only lasting a few minutes on a power outage. I found that they were using
the VA rating as Watts. They ended up having to get the larger UPS's
You're probably right that some people are buying smaller units than
they need based on the VA rating, but it's hard to fault the
manufacturer for being accurate (I'm not vouching for APC, but it's
_sounds_ like the're rating it accurately). Also, if the shopper knows
he needs a higher VA rating, he'd buy a larger unit, which would be to
Does the ouput rating only say 950W, or 950W at .x power factor? If
it's really a 1400 VA unit, you should get 1400W if your power factor
Those ferro-resonant transformers have rather large core losses. Just
allow it to idle for a couple of hours and note the heat being blown out by
the fan. I would leave the unit UNplugged except when you need it and keep
the battery up with a good smart trickle charger.
thanks Vaughn, it is not a bad idea. I will have the isolation switch
anyway, thanks to gunner's and others' tips, so I can easily
accommodate a trickle charger which I already own.
Quick question... Will that ferrups UPS charge any capacity battery,
or only the specific one that comes with it?
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