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Something that has always bugged me about UPSes

Demon-Xanth

Demon-Xanth

Lifer
...they don't list Ah ratings. Why not? That will tell you how long they'll actually run. I don't care if it can drive eleventy billion watts if the battery will only power it for five seconds. Give me the Ah rating, I know it's not hard, it's on the battery inside of it. Just put it on the box on the outside where people can see it.
 
Originally posted by: TuxDave
Originally posted by: aigomorla
Originally posted by: Gibson486
b/c it is dependant on the load.
Click to expand...

^ this..

thats why they give you capacity.. VA.
Click to expand...

Volt * Amp = Watt?
Click to expand...

Because of power factors, reactance, and peak currents, volt amps and watts aren't the same. But neither VA nor watts tells you what the hold capacity is. I've seen some UPS with ridiculously small batteries. Think of watts like torque, VA like HP, and Ah like gas tank size.
 
Originally posted by: Gibson486
b/c it is dependant on the load.
Click to expand...

Why is that? Amp*Hours = Coulumbs of charge that the UPS holds and assuming its rated at a fixed output voltage, you can imply that it's that amount of charge at that voltage so you can get total energy stored in the UPS, all of which is independent of the load (at least in the theoretical sense).

Duration can then be derived given the load and the above number.
 
Originally posted by: TuxDave
Originally posted by: Gibson486
b/c it is dependant on the load.
Click to expand...

Why is that? Amp*Hours = Coulumbs of charge that the UPS holds and assuming its rated at a fixed output voltage, you can imply that it's that amount of charge at that voltage so you can get total energy stored in the UPS, all of which is independent of the load (at least in the theoretical sense).

Duration can then be derived given the load and the above number.
Click to expand...

The loses involved in the power conversion and the internal resistance of the battery will vary with load. But I still think that stating the Ah rating would be useful when comparing UPSes.
 
Originally posted by: Demon-Xanth
Originally posted by: TuxDave
Originally posted by: aigomorla
Originally posted by: Gibson486
b/c it is dependant on the load.
Click to expand...

^ this..

thats why they give you capacity.. VA.
Click to expand...

Volt * Amp = Watt?
Click to expand...

Because of power factors, reactance, and peak currents, volt amps and watts aren't the same. But neither VA nor watts tells you what the hold capacity is. I've seen some UPS with ridiculously small batteries. Think of watts like torque, VA like HP, and Ah like gas tank size.
Click to expand...

Unfortunately my EE knowledge far exceeds my car knowledge so I'll keep with the traditional definitions of electricity. 🙂 But yeah I forgot that UPS doesn't drive a DC power so I ignored the factors you addressed above.
 
Originally posted by: Demon-Xanth
Originally posted by: TuxDave
Originally posted by: aigomorla
Originally posted by: Gibson486
b/c it is dependant on the load.
Click to expand...

^ this..

thats why they give you capacity.. VA.
Click to expand...

Volt * Amp = Watt?
Click to expand...

Because of power factors, reactance, and peak currents, volt amps and watts aren't the same. But neither VA nor watts tells you what the hold capacity is. I've seen some UPS with ridiculously small batteries. Think of watts like torque, VA like HP, and Ah like gas tank size.
Click to expand...

they are both power quantities, but watts is true power while VA is apparent power (and deals with the rms value of voltage).

VA and watts tell you what the UPS is able to produce. If the the load is purely resistive, then all you care about it wattage. If the load has some reactance, you care about VA.

Also, your analogy is kind of off.
 
Originally posted by: Gibson486
they are both power quantities, but watts is true power while VA is apparent power (and deals with the rms value of voltage).

VA and watts tell you what the UPS is able to produce. If the the load is purely resistive, then all you care about it wattage. If the load has some reactance, you care about VA.

Also, your analogy is kind of off.
Click to expand...

My point is that neither tell you how LONG it will deliver that power. You just go on faith that higher VA=more AH.
 
Originally posted by: TuxDave
Originally posted by: Gibson486
b/c it is dependant on the load.
Click to expand...

Why is that? Amp*Hours = Coulumbs of charge that the UPS holds and assuming its rated at a fixed output voltage, you can imply that it's that amount of charge at that voltage so you can get total energy stored in the UPS, all of which is independent of the load (at least in the theoretical sense).

Duration can then be derived given the load and the above number.
Click to expand...

it tells you watt the charge is, yeah....but some loads are more reactive than others. Your thinking works for purely resistive loads with a fixed voltage, but UPS manufcatures have no idea if that is always going to be the case.

If you hook the UPS to to a computer, you cannot go by Ah b/c the computers switching power supply is almost purely inductive (reactive). Once you get a reactive load, things are not so linear anymore, which is why Ah will not work.
 
As Gibson486 is saying, Ah is basically useless for your needs. And anyways, you can find runtime at places like this.

A better car analogy is that you are wanting to know how many miles you can drive on the undersized temporary spare tire. Sure, more miles is better. But the main reason for that spare is to let you get a few miles to get the original tire fixed or buy a new tire. The difference between 50 miles and 100 miles isn't much since you really should try to only drive on it for a few miles. The small spare isn't meant to be used a long time. Same with UPS - it gives you time to close everything down properly and it isn't intended to be used for a long time.
 
Originally posted by: dullard
As Gibson486 is saying, Ah is basically useless for your needs. And anyways, you can find runtime at places like this.

A better car analogy is that you are wanting to know how many miles you can drive on the undersized temporary spare tire. Sure, more miles is better. But the main reason for that spare is to let you get a few miles to get the original tire fixed or buy a new tire. The difference between 50 miles and 100 miles isn't much since you really should try to only drive on it for a few miles. The small spare isn't meant to be used a long time. Same with UPS - it gives you time to close everything down properly and it isn't intended to be used for a long time.
Click to expand...

No offense, but I trust those numbers like I trust run times from laptop manufacturers.
 
Originally posted by: Demon-Xanth
No offense, but I trust those numbers like I trust run times from laptop manufacturers.
Click to expand...
So, what you are saying is that you don't trust the manufacturer's website to tell you the information you want, but instead you want the manufacturer to print that same information on the UPS? No offense, but why on earth would you trust one and not the other? Either both are accurate or both are false. There is no reason for the manufacturer to print correct information on the UPS but lie on the website.
 
If your PC is the only thing connected and it has a PSU with active PFC, the VA will = W. Then I think there's a time rating for the UPS...
 
Originally posted by: dullard
Originally posted by: Demon-Xanth
No offense, but I trust those numbers like I trust run times from laptop manufacturers.
Click to expand...
So, what you are saying is that you don't trust the manufacturer's website to tell you the information you want, but instead you want the manufacturer to print that same information on the UPS? No offense, but why on earth would you trust one and not the other? Either both are accurate or both are false. There is no reason for the manufacturer to print correct information on the UPS but lie on the website.
Click to expand...

Ah is something that can be quantitatively measured and verified. "About 3 minutes for a typical system" isn't.
 
I measure UPSes with my arm.. If I can't lift it up by myself, it's got enough juice to run my pc for at least an hour.
 
Originally posted by: Demon-Xanth
Originally posted by: dullard
Originally posted by: Demon-Xanth
No offense, but I trust those numbers like I trust run times from laptop manufacturers.
Click to expand...
So, what you are saying is that you don't trust the manufacturer's website to tell you the information you want, but instead you want the manufacturer to print that same information on the UPS? No offense, but why on earth would you trust one and not the other? Either both are accurate or both are false. There is no reason for the manufacturer to print correct information on the UPS but lie on the website.
Click to expand...

Ah is something that can be quantitatively measured and verified. "About 3 minutes for a typical system" isn't.
Click to expand...

lol....they give you half load and full load conditions. They even give you a chart. It's more than enough for a ball park estimate. What more do you need? Again, you can't use Ah unless you want to know the uptime for one specific product.

Also, I actually size these for SCADA panels. APC's estimates are usually in the ballpark. I mean, it's not accurate to +/- 1% (it would be impossible for them to do that, so they have to use a "typical system"). I have also done actual calculations to figure out what my actual uptime will be and the numbers usually in the same area I am.
 
Their stupid. They should just tell you how long the battery will last instead of giving us all these bs numbers.
 
Originally posted by: blahblah99
I measure UPSes with my arm.. If I can't lift it up by myself, it's got enough juice to run my pc for at least an hour.
Click to expand...

that is so....unorthadox....but I can actually seeing it working.
 
Originally posted by: blahblah99
I measure UPSes with my arm.. If I can't lift it up by myself, it's got enough juice to run my pc for at least an hour.
Click to expand...

u r weak

i used to have a smartups (1500???). it weighed 70lbs.
it powered my computer, and dual 20" LCD for 6hrs
 
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