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From: wmartin <wwm@wwmartin.net>
Newsgroups: sci.electronics.design
Subject: Re: energy in UK
Date: Thu, 17 Apr 2025 21:44:31 -0700
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On 4/17/25 16:57, KevinJ93 wrote:
> On 4/17/25 1:50 PM, Carlos E.R. wrote:
>> On 2025-04-17 21:05, KevinJ93 wrote:
>>> On 4/17/25 2:28 AM, Don Y wrote:
>>>> On 4/16/2025 6:55 PM, KevinJ93 wrote:
>>>>> On 4/16/25 3:49 PM, Don Y wrote:
>>>>>  > On 4/16/2025 3:11 AM, Martin Brown wrote:
>>>>> <...>
>>>>>  > Here, the issue is the high PEAK demands that the ACbrrs place on
>>>>>  > individual
>>>>>  > subscribers.  We could probably get by on a 3-5KW plant -- but, 
>>>>> only if
>>>>>  > we could store and deliver for large loads (I think the ACbrr is 
>>>>> ~14KW).
>>>>>
>>>>> That's a very large residential A/C. Our 4-Ton unit (48kBTU/Hr) 
>>>>> takes about 5kW and suffices a 2,900 sq ft house in northern 
>>>>> California. (Don't you like all these antiquated units!)
>>>>
>>>> That's the startup load.  An inverter for a (pure) solar solution would
>>>> have to tolerate that for some large fraction of a second/seconds. 
>>>> I.e.,
>>>> you would NEED to be grid-tied in order to support such large loads,
>>>> even temporarily.
>>>>
>>>
>>> 14kW startup is about 60A LRA (locked Rotor Amperage). A single Tesla 
>>> Powerwall 3 battery is rated for 185A LRA and it is very common to 
>>> have two or more Powerwalls in a system which increases the available 
>>> short term power. Our A/C has a 104A LRA spec.
>>
>> What would happen if the inverter on the battery pack doesn't have 
>> that peak capacity?
> 
> The inverter would trip and power would be cutoff until reset.
> 
>> I mean, an inverter might simply limit the maximum peak current 
>> without destroying itself, keeping itself all the time within safe 
>> limits. Would the motor still start, albeit slowly? Or would it stall 
>> and overheat? Perhaps motors could be designed co cope. I know my AC 
>> unit has an inverter inside to control the motor, so does my fridge.
>>
>> ...
> 
> 
> 
The inverter can be smart enough to start up in "speed ramp" mode. I had 
the tripping issue on my 3hp lathe motor in high speed gear, until I 
programmed the inverter to ramp up to speed over several seconds. It's 
all about inertia in this case, maybe not so simple with a compressor 
load attached.