Is this scheme reasonable?

I have an automatic opening  trash can in the kitchen that runs off of
batteries. I wanna run it with a wall wart. When the lid opens it
draws more  power than the 750 mA wall wart I tried using to power it
could deliver. This makes sense. I don't want to use a bigger wall
wart and I don't want to have betteries in it all the time to provide
the current. I'm thinking instead of using a capacitor. If the current
and voltage draw as well as the duration to open the lid is measured
can that not be used to calculate the minimum size capacitor? And if
not excessive maybe a cap that would open the lid three or four times
in a row could be used in place of the 6 AA cells it uses now.
Reasonable?
Thanks,
Eric

On 5/10/2017 12:57 PM, etpm@whidbey.com wrote:
> I have an automatic opening  trash can in the kitchen that runs off of
> batteries. I wanna run it with a wall wart. When the lid opens it
> draws more  power than the 750 mA wall wart I tried using to power it
> could deliver. This makes sense. I don't want to use a bigger wall
> wart and I don't want to have betteries in it all the time to provide
> the current. I'm thinking instead of using a capacitor. If the current
> and voltage draw as well as the duration to open the lid is measured
> can that not be used to calculate the minimum size capacitor? And if
> not excessive maybe a cap that would open the lid three or four times
> in a row could be used in place of the 6 AA cells it uses now.
> Reasonable?

Sure, that's reasonable.  Rechargeable batteries may be a better 
solution.  For a cap to deliver 1 A for 1 second with a 1 volt droop 
requires 1 Farad, not microFarads, 1 FARAD!

If the cap only supplies the current required *above* the 750 mA 
provided by the wall wart, it might be able to be a bit smaller, but 
that depends on the actual current required.

I'm thinking rechargeable batteries with a built in charger.  How long 
do the AAs currently last?  Six Dollar tree AA cells cost $1.50. 
Rechargeables are several times that much.  Since it will be recharged 
often, you might get by with three AA or even AAA lithium ion cells or 
just a single rechargeable 9 volt battery.

-- 

Rick C

On Wed, 10 May 2017 09:57:21 -0700, etpm wrote:

> I have an automatic opening  trash can in the kitchen that runs off of
> batteries. I wanna run it with a wall wart. When the lid opens it draws
> more  power than the 750 mA wall wart I tried using to power it could
> deliver. This makes sense. I don't want to use a bigger wall wart and I
> don't want to have betteries in it all the time to provide the current.
> I'm thinking instead of using a capacitor. If the current and voltage
> draw as well as the duration to open the lid is measured can that not be
> used to calculate the minimum size capacitor? And if not excessive maybe
> a cap that would open the lid three or four times in a row could be used
> in place of the 6 AA cells it uses now. Reasonable?
> Thanks,
> Eric

This is kind of a repeat of what Rick said, from a different point of 
view:

For the amount of energy stored, caps are BIG.  And a capacitor's voltage 
falls as it delivers energy -- by definition.  If it doesn't, it's not a 
capacitor.

Rechargeable batteries are much smaller than caps -- and it's what the 
thing's designed for anyway.  The easiest thing to do, which should be 
reliable, is to populate the battery tray with rechargable NiMH cells, 
then put a charger on it that runs at a trickle rate (i.e., 50mA for 
every 1000mAh of capacity).  That _should_ let the batteries last a good 
long time, but whether it'll stay charged is kind of up in the air (or 
maybe it'll work fin normally but not on Thanksgiving or Christmas).

Make the charger from a wall-wart and a resistor.

The only other way I can think of to make this work "better" is with a 
smart charger -- and then you're messing with some pretty fancy 
electronics to keep the batteries happy.  So -- probably not a good idea.

Finally -- have you considered an old fashioned, works just fine, 
_mechanical_ covered trash can?

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!

On Wed, 10 May 2017 09:57:21 -0700, etpm@whidbey.com wrote:

>I have an automatic opening  trash can in the kitchen that runs off of
>batteries. I wanna run it with a wall wart. When the lid opens it
>draws more  power than the 750 mA wall wart I tried using to power it
>could deliver. This makes sense. I don't want to use a bigger wall
>wart and I don't want to have betteries in it all the time to provide
>the current. I'm thinking instead of using a capacitor. If the current
>and voltage draw as well as the duration to open the lid is measured
>can that not be used to calculate the minimum size capacitor? And if
>not excessive maybe a cap that would open the lid three or four times
>in a row could be used in place of the 6 AA cells it uses now.
>Reasonable?
>Thanks,
>Eric

A conventional cap, no. Maybe a super expensive supercap.

I wouldn't want an electronic trash can. All that cheap, badly
programmed microprocessor/LCD appliance junk will break in a couple of
years, and be annoying meanwhile.

*SIX* AA cells? How long do they last?


-- 

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement 

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

On Wed, 10 May 2017 11:31:40 -0700, John Larkin
<jjlarkin@highland_snip_technology.com> wrote:

>On Wed, 10 May 2017 09:57:21 -0700, etpm@whidbey.com wrote:
>
>>I have an automatic opening  trash can in the kitchen that runs off of
>>batteries. I wanna run it with a wall wart. When the lid opens it
>>draws more  power than the 750 mA wall wart I tried using to power it
>>could deliver. This makes sense. I don't want to use a bigger wall
>>wart and I don't want to have betteries in it all the time to provide
>>the current. I'm thinking instead of using a capacitor. If the current
>>and voltage draw as well as the duration to open the lid is measured
>>can that not be used to calculate the minimum size capacitor? And if
>>not excessive maybe a cap that would open the lid three or four times
>>in a row could be used in place of the 6 AA cells it uses now.
>>Reasonable?
>>Thanks,
>>Eric
>
>A conventional cap, no. Maybe a super expensive supercap.
>
>I wouldn't want an electronic trash can. All that cheap, badly
>programmed microprocessor/LCD appliance junk will break in a couple of
>years, and be annoying meanwhile.
>
>*SIX* AA cells? How long do they last?
Thanks for the quick responses everyone. It looks like rechargeable
cells are really the best way to go. The regular cells last about 3
months. I hate the garbage can. I hate throwing batteries in the
recycle bin. I hate the garbage can. It was advertised as motion
sensitive. It is not. It senses reflected IR, not motion. So if the
damn sensor is covered with IR reflective material the lid stays open.
Did you know that some clear plastic sheet reflects IR? Did I say I
hate the garbage can? Unfortunately for now it is the best solution.
Though a foot operated model is in the future right now it just won't
work.
Thanks Again,
Eric

On 5/10/2017 1:52 PM, Tim Wescott wrote:
> On Wed, 10 May 2017 09:57:21 -0700, etpm wrote:
>
>> I have an automatic opening  trash can in the kitchen that runs off of
>> batteries. I wanna run it with a wall wart. When the lid opens it draws
>> more  power than the 750 mA wall wart I tried using to power it could
>> deliver. This makes sense. I don't want to use a bigger wall wart and I
>> don't want to have betteries in it all the time to provide the current.
>> I'm thinking instead of using a capacitor. If the current and voltage
>> draw as well as the duration to open the lid is measured can that not be
>> used to calculate the minimum size capacitor? And if not excessive maybe
>> a cap that would open the lid three or four times in a row could be used
>> in place of the 6 AA cells it uses now. Reasonable?
>> Thanks,
>> Eric
>
> This is kind of a repeat of what Rick said, from a different point of
> view:
>
> For the amount of energy stored, caps are BIG.  And a capacitor's voltage
> falls as it delivers energy -- by definition.  If it doesn't, it's not a
> capacitor.
>
> Rechargeable batteries are much smaller than caps -- and it's what the
> thing's designed for anyway.  The easiest thing to do, which should be
> reliable, is to populate the battery tray with rechargable NiMH cells,
> then put a charger on it that runs at a trickle rate (i.e., 50mA for
> every 1000mAh of capacity).  That _should_ let the batteries last a good
> long time, but whether it'll stay charged is kind of up in the air (or
> maybe it'll work fin normally but not on Thanksgiving or Christmas).
>
> Make the charger from a wall-wart and a resistor.
>
> The only other way I can think of to make this work "better" is with a
> smart charger -- and then you're messing with some pretty fancy
> electronics to keep the batteries happy.  So -- probably not a good idea.
>
> Finally -- have you considered an old fashioned, works just fine,
> _mechanical_ covered trash can?

I think you have this pretty much backwards.  A "smart" battery charger 
is the only real way to go if you want the batteries to last.  The 
"trickle" charger may keep the batteries up given that most people don't 
use such a trash can for long periods, but once rechargeables are 
charged, they don't want more current unless they are lead acid.  I 
didn't look it up, so do you know that NiMH will take a trickle charge 
without damage?  I don't think I've heard of that.

Proper charging electronics doesn't need to be hard to design or use.

-- 

Rick C

On 05/10/2017 02:31 PM, John Larkin wrote:
> On Wed, 10 May 2017 09:57:21 -0700, etpm@whidbey.com wrote:
>
>> I have an automatic opening  trash can in the kitchen that runs off of
>> batteries. I wanna run it with a wall wart. When the lid opens it
>> draws more  power than the 750 mA wall wart I tried using to power it
>> could deliver. This makes sense. I don't want to use a bigger wall
>> wart and I don't want to have betteries in it all the time to provide
>> the current. I'm thinking instead of using a capacitor. If the current
>> and voltage draw as well as the duration to open the lid is measured
>> can that not be used to calculate the minimum size capacitor? And if
>> not excessive maybe a cap that would open the lid three or four times
>> in a row could be used in place of the 6 AA cells it uses now.
>> Reasonable?
>> Thanks,
>> Eric
>
> A conventional cap, no. Maybe a super expensive supercap.
>
> I wouldn't want an electronic trash can. All that cheap, badly
> programmed microprocessor/LCD appliance junk will break in a couple of
> years, and be annoying meanwhile.
>
> *SIX* AA cells? How long do they last?
>
>

A couple of supercaps in series might work fine.  For instance,
SCMT22C505MRBA0  AVX CAPACITOR 5F 20% 5V 0.065ohms $5.23000 in onesies 
from Digikey.

Two of those in series, with a TL431 across each one (set for 4.8V or 
so) to equalize the voltage, plus a charger with about a 50 mA current 
limit ought to work, I should think.

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

On Wed, 10 May 2017 11:31:40 -0700, John Larkin
<jjlarkin@highland_snip_technology.com> wrote:

>On Wed, 10 May 2017 09:57:21 -0700, etpm@whidbey.com wrote:
>
>>I have an automatic opening  trash can in the kitchen that runs off of
>>batteries. I wanna run it with a wall wart. When the lid opens it
>>draws more  power than the 750 mA wall wart I tried using to power it
>>could deliver. This makes sense. I don't want to use a bigger wall
>>wart and I don't want to have betteries in it all the time to provide
>>the current. I'm thinking instead of using a capacitor. If the current
>>and voltage draw as well as the duration to open the lid is measured
>>can that not be used to calculate the minimum size capacitor? And if
>>not excessive maybe a cap that would open the lid three or four times
>>in a row could be used in place of the 6 AA cells it uses now.
>>Reasonable?
>>Thanks,
>>Eric
>
>A conventional cap, no. Maybe a super expensive supercap.
>
>I wouldn't want an electronic trash can. All that cheap, badly
>programmed microprocessor/LCD appliance junk will break in a couple of
>years, and be annoying meanwhile.
>
>*SIX* AA cells? How long do they last?


I have some 2.7 volt 50 farad caps that cost $1.29/ea.  4 in series is
12.5 farads and might do the trick.  Add some solar cells...

I've been tinkering with them intending to run a strobe light I attach
to a buoy so I can find it with my kayak in the dark.  I've used
alkaline (3) AA cells to power it for 6 months (flashes 12 LEDs, 6
hours after dark until sun-up, that's when I kayak), I also tried a
store bought solar garden light with one 50 farad cap that works
pretty well but not as bright as the strobe which is visible from 2
miles on a good night, and 1/2 mile most nights.

On Wed, 10 May 2017 18:13:26 -0400, rickman wrote:

> On 5/10/2017 1:52 PM, Tim Wescott wrote:
>> On Wed, 10 May 2017 09:57:21 -0700, etpm wrote:
>>
>>> I have an automatic opening  trash can in the kitchen that runs off of
>>> batteries. I wanna run it with a wall wart. When the lid opens it
>>> draws more  power than the 750 mA wall wart I tried using to power it
>>> could deliver. This makes sense. I don't want to use a bigger wall
>>> wart and I don't want to have betteries in it all the time to provide
>>> the current. I'm thinking instead of using a capacitor. If the current
>>> and voltage draw as well as the duration to open the lid is measured
>>> can that not be used to calculate the minimum size capacitor? And if
>>> not excessive maybe a cap that would open the lid three or four times
>>> in a row could be used in place of the 6 AA cells it uses now.
>>> Reasonable?
>>> Thanks,
>>> Eric
>>
>> This is kind of a repeat of what Rick said, from a different point of
>> view:
>>
>> For the amount of energy stored, caps are BIG.  And a capacitor's
>> voltage falls as it delivers energy -- by definition.  If it doesn't,
>> it's not a capacitor.
>>
>> Rechargeable batteries are much smaller than caps -- and it's what the
>> thing's designed for anyway.  The easiest thing to do, which should be
>> reliable, is to populate the battery tray with rechargable NiMH cells,
>> then put a charger on it that runs at a trickle rate (i.e., 50mA for
>> every 1000mAh of capacity).  That _should_ let the batteries last a
>> good long time, but whether it'll stay charged is kind of up in the air
>> (or maybe it'll work fin normally but not on Thanksgiving or
>> Christmas).
>>
>> Make the charger from a wall-wart and a resistor.
>>
>> The only other way I can think of to make this work "better" is with a
>> smart charger -- and then you're messing with some pretty fancy
>> electronics to keep the batteries happy.  So -- probably not a good
>> idea.
>>
>> Finally -- have you considered an old fashioned, works just fine,
>> _mechanical_ covered trash can?
> 
> I think you have this pretty much backwards.  A "smart" battery charger
> is the only real way to go if you want the batteries to last.  The
> "trickle" charger may keep the batteries up given that most people don't
> use such a trash can for long periods, but once rechargeables are
> charged, they don't want more current unless they are lead acid.  I
> didn't look it up, so do you know that NiMH will take a trickle charge
> without damage?  I don't think I've heard of that.
> 
> Proper charging electronics doesn't need to be hard to design or use.

I know Eric from these groups, and I'm assuming that he doesn't want to 
run out and design a PCB just for a trash can.

Eric!!  "Accidentally" start a greasy paper towel on fire and toss it in 
the trash.  Then instead of putting the lid down, freak out and put the 
can on the porch where it won't burn down your house.

Then get a decent freaking garbage can!!!

-- 
www.wescottdesign.com

On 5/11/2017 11:32 AM, Tim Wescott wrote:
> On Wed, 10 May 2017 18:13:26 -0400, rickman wrote:
>
>> On 5/10/2017 1:52 PM, Tim Wescott wrote:
>>> On Wed, 10 May 2017 09:57:21 -0700, etpm wrote:
>>>
>>>> I have an automatic opening  trash can in the kitchen that runs off of
>>>> batteries. I wanna run it with a wall wart. When the lid opens it
>>>> draws more  power than the 750 mA wall wart I tried using to power it
>>>> could deliver. This makes sense. I don't want to use a bigger wall
>>>> wart and I don't want to have betteries in it all the time to provide
>>>> the current. I'm thinking instead of using a capacitor. If the current
>>>> and voltage draw as well as the duration to open the lid is measured
>>>> can that not be used to calculate the minimum size capacitor? And if
>>>> not excessive maybe a cap that would open the lid three or four times
>>>> in a row could be used in place of the 6 AA cells it uses now.
>>>> Reasonable?
>>>> Thanks,
>>>> Eric
>>>
>>> This is kind of a repeat of what Rick said, from a different point of
>>> view:
>>>
>>> For the amount of energy stored, caps are BIG.  And a capacitor's
>>> voltage falls as it delivers energy -- by definition.  If it doesn't,
>>> it's not a capacitor.
>>>
>>> Rechargeable batteries are much smaller than caps -- and it's what the
>>> thing's designed for anyway.  The easiest thing to do, which should be
>>> reliable, is to populate the battery tray with rechargable NiMH cells,
>>> then put a charger on it that runs at a trickle rate (i.e., 50mA for
>>> every 1000mAh of capacity).  That _should_ let the batteries last a
>>> good long time, but whether it'll stay charged is kind of up in the air
>>> (or maybe it'll work fin normally but not on Thanksgiving or
>>> Christmas).
>>>
>>> Make the charger from a wall-wart and a resistor.
>>>
>>> The only other way I can think of to make this work "better" is with a
>>> smart charger -- and then you're messing with some pretty fancy
>>> electronics to keep the batteries happy.  So -- probably not a good
>>> idea.
>>>
>>> Finally -- have you considered an old fashioned, works just fine,
>>> _mechanical_ covered trash can?
>>
>> I think you have this pretty much backwards.  A "smart" battery charger
>> is the only real way to go if you want the batteries to last.  The
>> "trickle" charger may keep the batteries up given that most people don't
>> use such a trash can for long periods, but once rechargeables are
>> charged, they don't want more current unless they are lead acid.  I
>> didn't look it up, so do you know that NiMH will take a trickle charge
>> without damage?  I don't think I've heard of that.
>>
>> Proper charging electronics doesn't need to be hard to design or use.
>
> I know Eric from these groups, and I'm assuming that he doesn't want to
> run out and design a PCB just for a trash can.

You seem to be unable to think outside the box many times.  I can't 
imagine building a PCB for a project like this.  I'd use an expression 
involving cats, but it is prohibited in this house.

-- 

Rick C