How to mesure run time with a KW/h rating. - Page 1
Forum section: electronics / beginners

author: electrolux
author_rank: Regular Contributor
timestamp: July 05, 2015, 04:22:16 pm
content: So, a battery is rated at: Nominal voltage: 393V Nominal energy: 23kWh.A motor is rated at: 450Arms 325VDC (Can handle 393V) (I am presuming 'arms' means 'amps')How do I measure the motors run time (Zero load) using the above battery?

author: SuzyC
author_rank: Frequent Contributor
timestamp: July 05, 2015, 04:33:04 pm
content: I donno what from watt, but what is a goceries man?

author: PSR B1257
author_rank: Frequent Contributor
timestamp: July 05, 2015, 04:38:35 pm
content: QuoteNo, it's ARMS(https://en.wikipedia.org/wiki/Root_mean_square)QuoteTry a stopwatchOr an amperemeter and a bit mathHowever, a 150kW motor and a battery with only 23kWh do not really match.

author: electrolux
author_rank: Regular Contributor
timestamp: July 05, 2015, 04:41:55 pm
content: Quote from: PSR B1257 on July 05, 2015, 04:38:35 pmHow did you know that the motor is 15kW?

author: electrolux
author_rank: Regular Contributor
timestamp: July 05, 2015, 04:43:31 pm
content: Quote from: SuzyC on July 05, 2015, 04:33:04 pmIs that a joke?

author: PSR B1257
author_rank: Frequent Contributor
timestamp: July 05, 2015, 04:56:08 pm
content: QuoteNot 15kW but 450A*325V=146250W close enough to 150kW (roughly estimated).

author: Lightages
author_rank: Unknown
timestamp: July 05, 2015, 05:10:22 pm
content: Quote from: electrolux on July 05, 2015, 04:22:16 pmThat would be 450 Amps RMS. The only way to measure the run time with no load is to measure the actual current being drawn with no load and then do the math, or let it run until it stops or reaches the low voltage limit for the batteries and time it. The motor rating is at full load so the numbers given are useless to determine run time with no load.

author: LukeW
author_rank: Frequent Contributor
timestamp: July 05, 2015, 05:13:56 pm
content: Quote from: electrolux on July 05, 2015, 04:22:16 pmIf you know how much energy a battery stores and you know how much power a load device draws then you can calculate how long you can flow energy out of the battery at that rate (power is the flow rate of energy, the time derivative) until all the stored energy is depleted.Note that one unit of energy measurement is watt-hours... that makes it pretty easy. If energy flows into (or from) a battery at a rate of 1 watt for 1 hour then the total amount of energy transferred is 1 watt-hour.

author: sunnyhighway
author_rank: Frequent Contributor
timestamp: July 05, 2015, 05:36:33 pm
content: Quote from: SuzyC on July 05, 2015, 04:33:04 pmI would categorize it as type-O.

author: electrolux
author_rank: Regular Contributor
timestamp: July 05, 2015, 05:58:33 pm
content: Quote from: PSR B1257 on July 05, 2015, 04:56:08 pmYes I meant 150kW, type-O.

author: suicidaleggroll
author_rank: Super Contributor
timestamp: July 05, 2015, 10:06:25 pm
content: 450Arms * 325V = 146.25kWrms23kWh / 146.25kW = 0.157h = 9.4 minutes, assuming zero loss in your voltage conversion and wiring and zero ESR on the battery. In reality it will be less than that, how much less depends on how significant those three sources of loss are. That is assuming the battery doesn't overheat and explode with that much current draw.

author: electrolux
author_rank: Regular Contributor
timestamp: July 06, 2015, 10:35:10 am
content: Quote from: suicidaleggroll on July 05, 2015, 10:06:25 pmYeah I guessed it would be something like that. But I've found some cells rated at 400A 3.2V and the motor should run for around 35-40 Mins on that.

author: Jeroen3
author_rank: Super Contributor
timestamp: July 06, 2015, 12:34:47 pm
content: Use the measurements on the motor drive display to determine run time.Or are you just hooking up the battery to the motor?

author: suicidaleggroll
author_rank: Super Contributor
timestamp: July 06, 2015, 01:06:38 pm
content: Quote from: electrolux on July 06, 2015, 10:35:10 amA 400A rating is not the same thing as a 400Ah rating. "400A" is a current rating, it means the cell can supply up to 400A without blowing up. "400Ah" is a capacity rating, it means it can supply 1A for 400 hours before it's depleted.If that was a typo and you meant 400Ah, then yes, you could stack 100 of those cells in series to get the voltage up, and then they could power the load for the greater part of an hour before they're depleted, provided they can supply 450A without blowing up.

author: electrolux
author_rank: Regular Contributor
timestamp: July 07, 2015, 01:07:03 pm
content: Quote from: suicidaleggroll on July 06, 2015, 01:06:38 pmIt is a type-o. The cells are rated for up to 4K amp current draw.http://www.ev-power.eu/Winston-40Ah-200Ah/WB-LYP400AHA-LiFeYPO4-3-2V-400Ah.html

author: onlooker
author_rank: Frequent Contributor
timestamp: July 08, 2015, 12:01:54 am
content: The "9.4 minutes" mentioned was a full load estimate; while the OP was asking a zero-load estimate. My guess would be 10 or more times the 9.4 number. Then, to be sure, you need, as already mentioned by others, either measure the zero-load current or just time it .

author: tggzzz
author_rank: Super Contributor
timestamp: July 08, 2015, 08:38:33 am
content: Quote from: electrolux on July 07, 2015, 01:07:03 pmThose are very serious batteries that contain alotof energy, ~4.5MJ. 1 ton of TNT contains 4.1GJ, so this this battery is equivalent to >1kg of TNT. Now you won't be able to get the energy out as fast as you can with TNT, but you will be able to get it out fast enough to do serious damage - particularly if the battery is shorted.Consider that 450A*3.3V=1.5kW, and that domestic electric heating elements (fires, stove/hob rings) get red hot and they are only 1kW.Be very careful that you have understood how your circuit and the battery will act when there are faults in either.

author: electrolux
author_rank: Regular Contributor
timestamp: July 09, 2015, 11:13:21 am
content: Yeah, I'm not planning to do it just yet...