Help With Math, Calculating Total Amps

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Unimatic1140

Unimatic1140

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Hello Applianceville, I have a question for you math experts.

Does anyone know the formula for calculating total AMPS? If I have three different units operating in parallel on the same circuit:

#1 6.5 Amps
#2 10.1 Amps
#3 2.1 Amps

What is the total AMP draw? I though you just add 6.5+10.1+2.1 = 18.7 AMPS but apparently it doesn't work that way, the number is something lower than 18.7. I know there is a formula to calculate this, does anyone know what it is?
 
25Hz power was used by railways to "combine" the advantages of DC and AC power.the 25Hz power could be transmitted and transformed by transformers like regular AC power.The frequency was low enough so electric locomotive DC motors could operate off it WITHOUT rectification.Modern AC loco motors weren/t available then-most electric locomotive designed involved DC motors.To control the speed on the electric 25Hz locomotive transformer tap changers were used-IN GG-1 locomotive the transformer had 25 taps-25 speeds.The top 9 speeds were locked out to prevent blowing the 25Hz feeders and overhead lines if two or more GG-1 were coupled together.They were rated at about 4700 HP each.
On Universal and Induction motors-universal(brush type) could produce high torque-but due to their small frame and armature windings-for only a short period of time.For the applications favoring universal motors-they pack a lot of power in a small and light size.Thats a good reason why "contractors table" saws have geared down universal motors-essentially a "skilsaw" gear motor mounted to the saw trunnions.If you put a 1.5Hp induction motor on the stand type contractors saw-it would be too heavy to lift-and too difficult to run from a generator or temporary power feed.That geared down universal motor in the saw could generate up to 3Hp.You just wouldn't want to rip Oak planks on it all day-that motor would overheat-the induction one would not.To put it another way-a 1.5Hp universal motor is lighter and smaller than the induction one and draws about half the amps.And since the universal motor has no start windings or caps,less start power.
A "rotary converter" could be considered a mechanical rectifier-a device to convert AC to DC-yes was most commonly used before the invention of mercury,seleenium,and silicone rectifiers.It could be considered an induction motor turning a DC generator.Pipe organs used them until present for the 12V relay and switching systems in the organs-the DC generator was often turned by the organ blower motor.Now most pipe organs have solid state rectifier systems.These are more compatible with the solid state logic and switching (digital) installed in organs today.Some very early broadcast transmitters had MANY Motor-gen converters in them-for tube filaments,Bias,Low voltage DC plate,and high voltage DC plate.Haven't worked on any of those-but read manuals on them just in case.Those transmitters had interlock systems in them so you couldn't activate the LV and HV plate supplies unless the filament and bias motor gens were on and generating voltage.Oh-Oh-got to sign off a transmitter--
 
You've got it right, just add them up.

If an appliance is rated for 10.1 amps that is the maximum current. If these units have motors, that is what they draw when they start. If they all start of once, you should blow a 15A breaker.

Ken D
 
Well the Unimatic is rated at 8AMPS on the model # plate, but on spin start up its amperage peaks for 15 seconds or so at 24 AMPS according to my AMP meter. I think most appliance ratings are peak operating AMPS, not the momentary start-up surge.

are the things which have a formula to evaluate them, and are less than the sum of the individual resistances.

I've heard this now from a few different sources and I'm wondering if anyone knows the formula?
 
unimatic1140 wrote:
"Well the Unimatic is rated at 8AMPS on the model # plate, but on spin start up its amperage peaks for 15 seconds or so at 24 AMPS according to my AMP meter. I think most appliance ratings are peak operating AMPS, not the momentary start-up surge."

**********************

Your mention of peak operating amps makes sense, but 15 seconds is too long to be called a start-up surge, and 24 amps can't be right, it would take out a 15 amp breaker for sure.

Test your amp meter, a 60W light bulb should read about half an amp.

Ken D.
 
Excuse My 'P'

Thanks Jon, I need to do some calculations for the Super Unimatic.

Ken, its 24 AMPS for sure; my 1955 Unimatic is 25 AMPS. I have multiple meters all are within five years old and they all read the same, even my old Frigidaire Wattmeter reads 24 AMPS when it’s converted to AMPS. The early Frigidaire Tech-Talk manuals have a discussion about this 24 AMP draw and tell the installers to make absolutely sure the washer is on a 15AMP time-delay fuse. It won’t take out a 15AMP circuit unless it’s left in the start winding for too long, but 15 seconds is well within its tolerance.
 
I did not know a time delay fuse would hold that much current for 15 seconds. Interesting. I bet the lights dim when it goes into spin!

I see this is for the Super Unimatic. Make sure the relay you use for the motor can handle the that current.

Ken D.
 
Yes the lights do dim a bit when it first goes into spin. I have each Unimatic on its own circuit so they can all go into spin at once. I have 200amp service in the house so its not an issue.

We have some great electronic surplus stores here that sell all kinds of electric and electronic parts real cheap. I bought several 16 amp (operating rating) relays to use for the motor, heater and pumps. The relays on the Computer Interface kit are only rated to 3 amps but I figure any component that draws over 1 amp I will use a 16 amp operating relay in between the board and the washer component to keep any electrical pressure off of the computer interface.
 
most circuit breakers are what's known as "time delay" Induction motors frequently draw several times the amount of power during starting as they do when running. For instance, the refrigerator I have pulls 2200 watts instantaiously when starting, but only 280 during running (using a "watts up" meter) Watts can be converted to amperes by taking wattage X voltage = amperes. The time delay fuse keeps the circuit from tripping during these surges. Start-up Surges however are rarely noted on the spec plate however. What you may be seeing as the max amperege draw is how much the machine would take with all it's features on. For instance, when the heater AND the motor in a dishwasher are both running at the same time.

Many times, the amerage draw is done from "lock up" power. In other words, if you were to get something in a blender that keeps the motor from turning, it will pull much more power than when the motor is freewheeling. This will be the maximum rating.

Maximum current ratings also take into account the motor type. There are two motors used typically in appliances. Induction motors are big, quiet, torquey and slow. These are usually found in most large appliances like washers, fans and other appliances that have continuous duty. Brushed motors are the exact opposite they are small, fast, noisey, and not very torquey. They are commonly found in power tools, blenders, vacuums, and other small locations. Frequently, they are geared down to the applicaion they are being used in. These motors do not require starting devices like induction motors do either. They will however pull much more power, and sometimes even burn out if locked up!
 
With speakers for example, two sets fo 8 ohm speaker will be a total resistance of only 4 ohms.

8Ohms over two paths = 4 Ohms. (8/4 =2 ) meaning the receiver will be passing more currnet than it wants to and the electronics can blow.

On a regular line-voltage circuit, more amps will flow with parallel loads becasue certainly the resistance to curren flow drops with each additional load. However the voltage in parallel cicruits stays the same (110v) to wach load; and the aperage IS the sum of the amps.

In series circuits the VOLTAGE is divided by the number of reistances/loads. For example to use a 600V DC subway 3rd rail for task lighting on the tracks they simply put five 120 volt light bulbs in series; each one gets 120 volts.

OHM's Law (resistance) is
E= I*R
Where E is electomotive force (volts)
I is Ampreage (why I dont remeber) and
R is resistance, defined in ohms.

Once you know two the other can be figured out algebraically.
A 5,200 watt heating elemment on 220v is 23.63 amps

220v/23.63a =9.31 ohms, therefore

E/R = 120/9.31 the samee element on 120 volts is 12.88 amps *120 volts= 1,547 watts!

(remember the GE dryers in the 60's that had an element that could be used on either voltage?).

ALso think of a regualar house circuit. The more items plugged into ONE circuit the greater the amps. They are after all in parallel!
 
Subway lighting

I've seen those 5-lamp arrays inside the older lower Manhattain tunnels in NYC. I never thought about about them powering them off the third rail, but that makes perfect sense! The New York subway is pretty fascinating. One of the most fascinating things was how they used rotary converters to change the 25hz AC current into DC to power the trains in the days before solid-state rectifiers.
 
Electrifying subject matter....

ok, do tell...

What 25hz AC?

I guess that is why old incandescent subway bulbs/lamps would "strobe" noticably.

So what is a rotary converter?

Thought to ponder:
Can't I have ONE post/thread that doesn't turn to AC/DC?
LOL

Come to think of it I beleive the AMPS are the AMPS just add em up. But the OHMS (resistance) would be by formula for parallel loads. Does this make ANY sense?

In the speaker example, I meant to say:
2 sets of 8 Ohm speakers connected in parallel.
 
Not to derail this thread, but wasn't there a topic a while back about a Watts-Up meter? I tried a search last night but came up empty handed... I've been thinking it'd be handy to perform some real-world tests. Anyone out there have one??

Cory
 
Rotary converters

"A "rotary converter" could be considered a mechanical rectifier-a device to convert AC to DC-yes was most commonly used before the invention of mercury,seleenium,and silicone rectifiers.It could be considered an induction motor turning a DC generator."

Actually, that was a later development, whereas the AC motor and DC generator were combined electrically into one unit. Older machines were actually "M-G" (motor generator) sets and consisted of an AC motor turning a DC generator via a shaft and were totaly separate electrically.

And yes, simply totalling up the amps is the way to get total amp draw. The plate rating doesn't take into account the starting surge.
 
Motor Gen sets

Yes the older models would be like combined-have some older electrical books that discuss them.I was thinking of the later models that had an induction(or synchronous motor for really large ones)Has anyone seen an elevator machine room?-You will find a M-G set there-they work really well in this application.most larger elevators have DC motors to drive the host mechanism for the car.Its said when the elevator car is descending-the elevator host motor is acting like a generator.The motor gen sets don't mind the voltage fed back into them and "cushions" the descent by acting as a active load for the host motor.Besides boiler rooms-elevator rooms are fascinating to me.Have enjoyed watching the quipment-on mid shifts you had to have work collegues take rides so you could watch the equipment.And vice versa.The elevator motors come as two types-direct drive traction-the motor is connected directly to the host capstan.Gear drive-the motor drives the elevator cable capstan thru a geared down gearbox-for even greater torque.Used on freight elevators.Passenger elevators use the direct drive traction system-for greater speed.the elevator motors are compound wound DC.New motors are permenent magnet DC with solid state control and recification systems.Would like to see one of those-but would miss the hum of the MG set and the clacking of the relays.If you can tour an elevator machine room-do so-you may be fascinated!!Sorry I drifted-another place where MG units are used.
Some of those are used as a UPS of sorts-years ago saw some Kato sets at Western Union relay site in Wash DC.Was in the coolest "art Deco" building.The units have 4 devices coupled together.--An induction motor running off the power line-A 300lb flywheel,and a DC Gen or motor-lastly a Deisel engine coupled by an overrunning clutch.the big advantage of this setup is TOTAL powerline isolation.Great for electroncs gear.No surges from the lines will get into it like with transformer-rectifier systems.Under normal use the AC induction motor powers the DC device and it charges a battery bank.the AC gen powers the equipment.If the line fails-the DC device can act as a motor and run from the batteries-again turning the AC generator and powering the equipment.As the batteries run down and if power hasn't been restored-the spinning flywheel helps start the Deisel motor and it will turn the AC gen-the DC device so it can recharge the batteries and run the equipment until the power goes back on.they said the Deisel engine could run for several days from the fuel they have.Was a very interesting setup-hadn't seen another like it.and it explains why they didn't have too many failures in their equipment.Even in this modern age MG's DO have some advantages.They could run loads that could be detrimental to SS supplies-and won't pass powerline surges.
 
I've got a Watts-Up meter. That's how I arrived at the numbers in my post on my fridge. Smarthome.com has them for $99.95. I have found them to be quite useful for measuring power consumption in appliances and for my job when troubleshooting!
 
Hi Robert

You just add the amperages.

The formula you are probably thinking of is for resistors in parallel:

total resistance is the reciprocal of the sum of the reciprocals of the individual resistors (in amps).
The reciprocal of a number is one over the number, eg reciprocal of 4 is 1/4.
the reciprocal of a fraction is to turn the fraction upside down, ie the reciprocal of 2/3 is 3/2.

Sorry but I'm not too good at typing this up, but I'll give it a go.

For example:

what is the total resistance of a 2 ohm resistor and a 4 ohm resistor in parallel?

reciprocals of 2 and 4 are 1/2 and 1/4.

add the reciprocals:
1/2 + 1/4 = 2/4 + 1/4 = 3/4

reciprocal of that is the answer:

reciprocal of 3/4 is 4/3 = 1 1/3.

So the answer is 1 1/3 ohms, or 1.33 ohms.

Chris.
 
Cool subway page!

This page is filled with THOUSANDS of pictures of the New York subway system, trains, and other lore. There's all sorts of technical information here too, including how the rail system was powered. Back in 1903 when the subway system was installed, there were a multitude of competing electrical companies (Remember Edison's DC, and Westinghouse's AC?) not to mention the fact that some neighborhoods didn't even have electricity yet. The New York subway system had to produce it's own power because of this. They chose 25hz AC just like larger electric trains were using to transmit it around the city, and converted it to DC in rotary converters to power the motors to in the trains. DC was much easier for speed control in multitude of stops of the urban system.

In the days before solid state recitifiers, AC was converted to DC using a device that looked similar to a giant generator, but what it used was a series of brushes that would "turn over" at the same frequency as the AC current, effectively converting it to DC. Take a look at the sub station pictures in the NYC subway.org site!

http://nycsubway.org
 
another thought

Maybe you are thinking of power factor??

I'm not at all clear on power factor, but it plays around with the amps, meaning that amps in an AC circuit can be less than or more than you would expect.

MY very vague understanding: say a motor is 240 volt 480 watt. You would expect it to draw 2 amps.

(volts x amps = watts)

But the power factor of the motor can influence the amps draw.

I can explain it roughly if anyone would like but it can get a bit drawn out... basically it's to do with the AC volts and AC amps being out of phase, so that the simple equation doesn't work.

It becomes relevant when operating machinery on an inverter or a generator, you need to have a generator capable of more watts than the appliance to be used on it states on the name plate.

Anyway I'm getting out of my depth here...
chris.
 
Yes Robert Gizmo is correct

you just add the amperages together linearly. I was thinking of the resistances in parallel.

( Robert wanted me to post my correction so that everybody would know his hunch was correct ---OY! ThaT Boy!)

I was looking into cycloconverters last year for converting our 60 HZ into 50 HZ, they are big, expensive and ugly! I wanted to ship over a new induction cooktop from Europe BUT NOW I can just go to Sears and slap down my Sears card and BOOM BOOM DONE I've got new Induction.
 
AC to DC

"In the days before solid state recitifiers, AC was converted to DC using a device that looked similar to a giant generator, but what it used was a series of brushes that would "turn over" at the same frequency as the AC current, effectively converting it to DC."

That's the device that superseded the MG sets. They were what were refered to as rotary or "synchronus" convertors. These and MG sets were in use in San Francisco to power their streetcar and electric trolleybus system up into the 80's
 
Thanks Jon and everyone! OK now I know that when I'm running the Super Hot Cycle (or what ever I call it) I'll be using:

Unimatic Mechanism Pulsating = 6.5 Amps
Heater = 10.0 Amps
Recirculation Pump = 2.1 Amps

Total Max Amp Draw = 18.6.

Since the washer will be plugged into a 20 amp breaker that should be just fine for the 12 min wash period with occasional recirculating heated-soaks thrown in for another 8 or so minutes at 12.1 amps. The rest of the time will be a much lower AMP draw, as well as when I run warm and cool water cycles.

While the computer to run the washer will be plugged into a different outlet, I'm going to assume that computers probably draw very little amperage.
 
My Frigemore has a nameplate rating of 12A. I have run it through full cycles with a recording ammeter, and the max run amps would be about 6A with brief 9A surges.

Manufacturers are free to put whatever value they want on a nameplate. According to the National Electrical Code, 12A is the maximum load on a 15A circuit, and any appliance with a nameplate current exceeding 50% of the circuit rating needs a dedicated circuit.

Nameplate current of 12A is manufacturer warranty CYA.

Use a clamp-on ammeter with each machine. Take the highest running amperage of each, add them up, and then add 25% of the highest rating.
 

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