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On Tue, 16 Oct 2007 04:07:28 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:
>> Fair enough, but I assume it would provide extra smoothing which may
>> or may not be of advantage here. I still can't find out what the
>> smoothness requirements are for these Chinese scooter motor
>> controllers.
>
>Very little I expect. It's just a motor.
And a PWM speed controller.
>> An guy on another group with experience with these things
>> thinks it needs a pretty smooth supply, as there is little power
>> conditioning in them as they are designed for batteries.
>
>Not actually relevant as far as I can see.
Well don't most electronic machines designed to plug into the mains
have considerable power conditioning in them? I know my computer PS
certainly does.
>> But he says the only way to find out is to try.
>
>That's right of course.
Yes, but surely a prudent experimenter will do at least a bit of
background research first to avoid duplicating many of the mistakes of
others. I would rather start from an over-engineered setup and work
backwards, if there is an advantage in doing so
>> BTW, he has given me
>> alternative ways to smooth the PS output as his calculations for the
>> required smoothness come out with a 3F capacitor which will be
>> expensive. jack
>
>He's a grade one IDIOT if he's talking about 3F capacitors. I'd take any advice
>of his with more than a pinch of salt.
He worked it out from first principles using slightly different input
data. Would you like to see his workings?
So who is the grade one idiot between you and the Evox Rifa folk whose
formula tells me I need only 10,800 uF - less than half your
calculation? :)
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On Tue, 16 Oct 2007 04:10:54 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:
>
>
>spamfree@spam.heaven wrote:
>
>> Eeyore wrote:
>> >spamfree@spam.heaven wrote:
>> >> Eeyore wrote:
>> >> >spamfree@spam.heaven wrote:
>> >> >> Eeyore wrote:
>> >>
>> >> >> >Your load is ~ 15A.
>> >> >>
>> >> >> More like 20, isn't it?
>> >> >
>> >> >20A x 36V = 720 W !
>> >>
>> >> That's about right. The motor is not perfect and its 500W output will
>> >> require something like that flat out.
>> >
>> >Hang on. Who said 500W *output* equals 720W input ? Where did you get such
an idea ? Why
>> >do you think the motor's rated in that way ?
>> >
>> >If it says '500W' I'd expect it to mean 500W input power.
>>
>> Well you would disagree with NEMA. jack
>
>Can you explain what you mean by that ? NEMA has no real relevance in this matter.
NEMA are in charge of electric motor labelling standards, I thought.
Surely that's entirely relevant. jack
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On Tue, 16 Oct 2007 04:14:58 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:
>
>
>spamfree@spam.heaven wrote:
>
>> Eeyore wrote:
>> >BobG wrote:
>> >
>> >> maybe just the secondary of a transformer would work?
>> >
>> >That would probably be a poor choice actually.
>> >
>> >Transformers are designed for AC not DC. The core will probably just
saturate
>> >and you'll merely add some DC resistance.
>>
>> I'm not even off the starting blocks wrt smoothing inductors.
>> Is a coil a useful addition?
>
>Not IMHO. In any event, at low voltage and high currents, the sizes required to do
>anything useful become absurd.
Thanks for that. Probably why they are not often used :)
jack
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On Tue, 16 Oct 2007 04:16:31 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:
>
>
>spamfree@spam.heaven wrote:
>
>> Eeyore wrote:
>> >spamfree@spam.heaven wrote:
>> >
>> >Eh ? They have a 50V rating. Why not use it ?
>>
>> Yes, and I've seen quoted a 63V surge capability, but what I wanted
>> assurance of is the need or not of some multiple of a safety factor.
>> Thanks for that, jack
>
>The 50V (63V surge) rating will be more than adequate, despite what some weirdos
>seem to think. Ignore the voodoo.
I wonder why the Evox Rifa folk worry about transients and spikes.
jack
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On Tue, 16 Oct 2007 04:21:04 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:
>
>
>spamfree@spam.heaven wrote:
>
>> On Mon, 15 Oct 2007 15:22:26 -0700, Tim Wescott <tim@seemywebsite.com>
>> wrote:
>>
>> >Yes, you can use the itty bitty caps. Verify their current ratings if
>> >you can -- some of what makes the spendy caps spendy is the AC ripple
>> >current they can deliver without overheating.
>>
>> I'm confused. This ripple current is surely what I want the caps to
>> absorb, not to deliver, or am I on the wrong tack as usual? :)
>
>The caps do both. They 'absorb' the current as the cap is recharged at the peak
>of the input voltage from the transformer/rectifier and then deliver it to the
>load when that input is providing no more charge. You see the
>transformer/rectifier deleivers the input power in 'blips' every 10ms and the
>caps job ios to smooth it out.
Yes, I understand the buffering effect, but had not thought of the
caps as producing their own ripple.
>> Anyways, it seems that the increased surface area of many small caps
>> over one big one would favour heat dissipation.
>
>They won't run so hot they need forced cooling as you suggested elsewhere.
>
>
>> Just depends on what
>> you can get your hands on for reasonable moolah. Seventy-five cents
>> for 4700uF seems pretty good value?
>
>It's OK
>
>
>> >You can parallel as many caps as you want, for more capacity and
>> >current. 50V isn't enough for a 36V supply.
>>
>> Someone jumped on me for suspecting this :)
>
>His advice above is utter nonsense based on nothing more than 'old wives tales'.
Thanks, jack
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Author: EeyoreDate: 23:01 15-10-07
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Roger Dewhurst wrote:
> "Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote
> >
> > I'd look further. Can't Dick Smith ? Electronics offer these ?
>
> Regrettably Dick Smith Electronics, now owned by Woolworths, is getting out
> of electronic components and into televisions etc.
Isn't that always how it goes in the end ?
Graham
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Author: ehsjrDate: 23:02 15-10-07
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spamfree@spam.heaven wrote:
> On Mon, 15 Oct 2007 17:43:58 +0100, Eeyore
> <rabbitsfriendsandrelations@hotmail.com> wrote:
>
>
>>
>>spamfree@spam.heaven wrote:
>>
>>
>>>Eeyore wrote:
>>>
>>>>spamfree@spam.heaven wrote:
>>>>
>>>>>from:
>>>>>C:\Documents and Settings\Administrator\Desktop\Power Supplies.mht
>>>>
>>>>A curious 'cookbook' equation. Mine is from electronics first
principles.
>>>
>>>Well, yes, I assumed that. but is it not useful? It's within an order
>>>of magnitude. What would be the downside of using twice the
>>>capacitance here?
>>
>>Unnecessary cost for one !
>
>
> Fair enough, but I assume it would provide extra smoothing which may
> or may not be of advantage here. I still can't find out what the
> smoothness requirements are for these Chinese scooter motor
> controllers. An guy on another group with experience with these things
> thinks it needs a pretty smooth supply, as there is little power
> conditioning in them as they are designed for batteries.
> But he says the only way to find out is to try. BTW, he has given me
> alternative ways to smooth the PS output as his calculations for the
> required smoothness come out with a 3F capacitor which will be
> expensive. jack
Using more capacitance increases the surge current when you
first turn the thing on. You might be able to "split out"
the supply to provide the controller logic with extremely
smooth power even if there is a lot of ripple.
Conceptually, it's like this:
+ 36 -----+-----------------------+
| a |
[D1] [Motor]
| |
+-----------+ |
| | |
[4700 uF] [Logic]---[MotorDriver]
| | |
Gnd ------+-----------+-----------+
The control logic draws *much* lower current than the
motor. The cap keeps the supply to the logic smooth -
the diode keeps the motor from discharging the cap.
Whether you can get inside the controller to add
a diode and cap is an unknown.
Actually, I suspect the existing circuit uses something
like that already, but that is a guess - I'm not familiar
with these scooters or their controllers.
Ed
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Author: EeyoreDate: 23:02 15-10-07
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BobG wrote:
> Eeyore wrote:
> > BobG wrote:
> > > maybe just the secondary of a transformer would work?
> >
> > That would probably be a poor choice actually.
> >
> > Transformers are designed for AC not DC. The core will probably just saturate
> > and you'll merely add some DC resistance.
> >
> > Graham
> =============================
> If he needs 15A and 'as much L as he can get', seems like any trans
> with a 15A secondary satisfies the amperage req, and you just live
> with whatever L is avail. I think I recall guitar amps having a 5H
> filter choke, but thats at 500VDC and ma instead of Amps. Whats the L
> of a power trans secondary if the primary is floating?
I don't know but if the core's saturated (as it will be) it's not going to be much
use to you.
Graham
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Author: EeyoreDate: 23:04 15-10-07
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Tim Wescott wrote:
> You can parallel as many caps as you want, for more capacity and
> current. 50V isn't enough for a 36V supply.
Utter nonsense.
Why do you think they make caps with a voltage rating ?
Graham
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Author: EeyoreDate: 23:07 15-10-07
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spamfree@spam.heaven wrote:
> Eeyore wrote:
> >spamfree@spam.heaven wrote:
> >> Eeyore wrote:
> >> >spamfree@spam.heaven wrote:
> >> >>
> >> >> from:
> >> >> C:\Documents and Settings\Administrator\Desktop\Power
Supplies.mht
> >> >
> >> >A curious 'cookbook' equation. Mine is from electronics first
principles.
> >>
> >> Well, yes, I assumed that. but is it not useful? It's within an order
> >> of magnitude. What would be the downside of using twice the
> >> capacitance here?
> >
> >Unnecessary cost for one !
>
> Fair enough, but I assume it would provide extra smoothing which may
> or may not be of advantage here. I still can't find out what the
> smoothness requirements are for these Chinese scooter motor
> controllers.
Very little I expect. It's just a motor.
> An guy on another group with experience with these things
> thinks it needs a pretty smooth supply, as there is little power
> conditioning in them as they are designed for batteries.
Not actually relevant as far as I can see.
> But he says the only way to find out is to try.
That's right of course.
> BTW, he has given me
> alternative ways to smooth the PS output as his calculations for the
> required smoothness come out with a 3F capacitor which will be
> expensive. jack
He's a grade one IDIOT if he's talking about 3F capacitors. I'd take any advice
of his with more than a pinch of salt.
Graham
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Author: EeyoreDate: 23:10 15-10-07
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spamfree@spam.heaven wrote:
> Eeyore wrote:
> >spamfree@spam.heaven wrote:
> >> Eeyore wrote:
> >> >spamfree@spam.heaven wrote:
> >> >> Eeyore wrote:
> >>
> >> >> >Your load is ~ 15A.
> >> >>
> >> >> More like 20, isn't it?
> >> >
> >> >20A x 36V = 720 W !
> >>
> >> That's about right. The motor is not perfect and its 500W output will
> >> require something like that flat out.
> >
> >Hang on. Who said 500W *output* equals 720W input ? Where did you get such an
idea ? Why
> >do you think the motor's rated in that way ?
> >
> >If it says '500W' I'd expect it to mean 500W input power.
>
> Well you would disagree with NEMA. jack
Can you explain what you mean by that ? NEMA has no real relevance in this matter.
Graham
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Author: EeyoreDate: 23:14 15-10-07
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spamfree@spam.heaven wrote:
> Eeyore wrote:
> >BobG wrote:
> >
> >> maybe just the secondary of a transformer would work?
> >
> >That would probably be a poor choice actually.
> >
> >Transformers are designed for AC not DC. The core will probably just saturate
> >and you'll merely add some DC resistance.
>
> I'm not even off the starting blocks wrt smoothing inductors.
> Is a coil a useful addition?
Not IMHO. In any event, at low voltage and high currents, the sizes required to do
anything useful become absurd.
Graham
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Author: EeyoreDate: 23:16 15-10-07
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spamfree@spam.heaven wrote:
> Eeyore wrote:
> >spamfree@spam.heaven wrote:
> >
> >Eh ? They have a 50V rating. Why not use it ?
>
> Yes, and I've seen quoted a 63V surge capability, but what I wanted
> assurance of is the need or not of some multiple of a safety factor.
> Thanks for that, jack
The 50V (63V surge) rating will be more than adequate, despite what some weirdos
seem to think. Ignore the voodoo.
Graham
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Author: EeyoreDate: 23:21 15-10-07
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spamfree@spam.heaven wrote:
> On Mon, 15 Oct 2007 15:22:26 -0700, Tim Wescott <tim@seemywebsite.com>
> wrote:
>
> >Yes, you can use the itty bitty caps. Verify their current ratings if
> >you can -- some of what makes the spendy caps spendy is the AC ripple
> >current they can deliver without overheating.
>
> I'm confused. This ripple current is surely what I want the caps to
> absorb, not to deliver, or am I on the wrong tack as usual? :)
The caps do both. They 'absorb' the current as the cap is recharged at the peak
of the input voltage from the transformer/rectifier and then deliver it to the
load when that input is providing no more charge. You see the
transformer/rectifier deleivers the input power in 'blips' every 10ms and the
caps job ios to smooth it out.
> Anyways, it seems that the increased surface area of many small caps
> over one big one would favour heat dissipation.
They won't run so hot they need forced cooling as you suggested elsewhere.
> Just depends on what
> you can get your hands on for reasonable moolah. Seventy-five cents
> for 4700uF seems pretty good value?
It's OK
> >You can parallel as many caps as you want, for more capacity and
> >current. 50V isn't enough for a 36V supply.
>
> Someone jumped on me for suspecting this :)
His advice above is utter nonsense based on nothing more than 'old wives tales'.
Graham
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Author: Roger DewhurstDate: 00:16 16-10-07
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"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:4714298B.1725C802@hotmail.com...
>
>
> Roger Dewhurst wrote:
>
>> "Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote
>> >
>> > I'd look further. Can't Dick Smith ? Electronics offer these ?
>>
>> Regrettably Dick Smith Electronics, now owned by Woolworths, is getting
>> out
>> of electronic components and into televisions etc.
>
> Isn't that always how it goes in the end ?
Yes. The fucking beancounters grab it and hold it until they cock it up
terminally. In the meantime someone else fills the gap.
R
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Author: EeyoreDate: 01:01 16-10-07
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spamfree@spam.heaven wrote:
> Eeyore wrote:
> >Tim Wescott wrote:
> >
> >> You can parallel as many caps as you want, for more capacity and
> >> current. 50V isn't enough for a 36V supply.
> >
> >Utter nonsense.
> >
> >Why do you think they make caps with a voltage rating ?
>
> I was worried about spikes and transients, like the Evox Rifa article
> warns about.
You won't see any spikes on a PSU reservoir cap. It would require a transient
with a huge energy to do that.
I suspect you've misread or misunderstood the app note. What page are you
referring to ?
Graham
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Author: EeyoreDate: 01:04 16-10-07
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spamfree@spam.heaven wrote:
> Eeyore wrote:
>
> >> Fair enough, but I assume it would provide extra smoothing which may
> >> or may not be of advantage here. I still can't find out what the
> >> smoothness requirements are for these Chinese scooter motor
> >> controllers.
> >
> >Very little I expect. It's just a motor.
>
> And a PWM speed controller.
So ? They'll work just fine with a bit of ripple too. You're fretting over things of
no consequence.
> >> An guy on another group with experience with these things
> >> thinks it needs a pretty smooth supply, as there is little power
> >> conditioning in them as they are designed for batteries.
> >
> >Not actually relevant as far as I can see.
>
> Well don't most electronic machines designed to plug into the mains
> have considerable power conditioning in them? I know my computer PS
> certainly does.
Completely different. Those circuits require a stable voltage for reason way outside
a simple discussion here. It's chalk and cheese. You're drawing false inferences.
Graham
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Author: EeyoreDate: 01:07 16-10-07
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spamfree@spam.heaven wrote:
> Eeyore wrote:
>
> >> BTW, he has given me
> >> alternative ways to smooth the PS output as his calculations for the
> >> required smoothness come out with a 3F capacitor which will be
> >> expensive. jack
> >
> >He's a grade one IDIOT if he's talking about 3F capacitors. I'd take any advice
> >of his with more than a pinch of salt.
>
> He worked it out from first principles using slightly different input
> data. Would you like to see his workings?
Why not. I'd like to see how he got something wrong by a factor of about 100:1 !
> So who is the grade one idiot between you and the Evox Rifa folk whose
> formula tells me I need only 10,800 uF - less than half your
> calculation? :)
Where do you get 10,800 uF from ?
If you actually paid atention to the equation I used you can determine what you
need for yourself. Let me tell you, 'cookbook' equations don't substitute for
calculating from first priciples which is what I did.
Graham
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Author: EeyoreDate: 01:11 16-10-07
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spamfree@spam.heaven wrote:
> Eeyore wrote:
> >spamfree@spam.heaven wrote:
> >> Eeyore wrote:
> >>
> >> >If it says '500W' I'd expect it to mean 500W input power.
> >>
> >> Well you would disagree with NEMA. jack
> >
> >Can you explain what you mean by that ? NEMA has no real relevance in this
matter.
>
> NEMA are in charge of electric motor labelling standards, I thought.
You thought WRONG.
NEMA is merely a US trade assocation and it's 'standards' or recomendations have no
authority
worldwide. Look for *** IEC ** standards instead.
IEC = International Electrotechnical Commission and all your Oz electrical standards are
based
on IEC ones, not some stupid US trade association like NEMA.
> Surely that's entirely relevant. jack
No it's not.
Graham
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Author: EeyoreDate: 01:11 16-10-07
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spamfree@spam.heaven wrote:
> Eeyore wrote:
> >spamfree@spam.heaven wrote:
>
> >>
> >> I'm not even off the starting blocks wrt smoothing inductors.
> >> Is a coil a useful addition?
> >
> >Not IMHO. In any event, at low voltage and high currents, the sizes required to
do
> >anything useful become absurd.
>
> Thanks for that. Probably why they are not often used :)
Precisely.
Graham
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