Re: Bally Mata Hari Question- Is bigger, better?
- From: "GPE" <GPEnospam@xxxxxxx>
- Date: Wed, 5 Dec 2007 18:44:27 -0600
"AL" <AL@xxxxxxxxxxx> wrote in message news:f302e64f-8299-4717-bb62-8bcc3eb61997@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Dec 5, 3:26 pm, "GPE" <GPEnos...@xxxxxxx> wrote:"AL" <A...@xxxxxxxxxxx> wrote in message
news:8176e1e4-e242-4a9f-b8f1-e9e3650793e2@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> On Dec 4, 11:13 pm, "GPE" <GPEnos...@xxxxxxx> wrote:
>> "AL" <A...@xxxxxxxxxxx> wrote in message
> > On Dec 4, 8:26 pm, "Tim N." <nobl...@xxxxxxxxx> wrote:
>> >> On Dec 4, 10:16 pm, AL <A...@xxxxxxxxxxx> wrote:
>> >> > On Dec 4, 7:04 pm, "Tim N." <nobl...@xxxxxxxxx> wrote:
>> >> > > I am replacing the C23 cap on the driver board. According to
>> >> > > Clay's
>> >> > > site- "Replace C23 with a new 10,000 to 15,000 mfd 20 volt
>> >> > > capacitor.
>> >> > > If your game has more than two flippers, use a 15,000 mfd cap. >> >> > > If
>> >> > > the
>> >> > > game only has two flippers, 10,000 or 12,000 mfd will work >> >> > > fine. "
>> >> > > I don't have any around that are in this size range (I know I >> >> > > can
>> >> > > order one), but I do have one that is 30,000mfd 25vdc... Will >> >> > > this
>> >> > > absolutely destroy this board, or is it something that can be
>> >> > > safely
>> >> > > installed?
>> >> > > Thanks for all input.... Even if it just means ordering a new
>> >> > > one...
>> >> > Tim,
>> >> > The original component is an 11,700ufd, 25V radial terminal
>> >> > Electrolytic Capacitor.
>> >> > IMO, replacing a cap based upon the number of flippers the game >> >> > has,
>> >> > somewhat defeats what Bally engineers strived for, which was >> >> > circuit
>> >> > familarity and board interchangeability.
>> >> > I would not go below the specified value, nor for saftey reasons, >> >> > go
>> >> > below the voltage rating. The 25V spec is fine. I feel the big
>> >> > debate
>> >> > will revolve around the capacity and it's increase of "inrush
>> >> > current". Personally, I don't see it as an issue, adding only a
>> >> > couple of milliseconds to the charge time constants.
>> >> > Does it physically occupy the same space?
>> >> > In this application, as a ripple filter and not related to a
>> >> > frequency
>> >> > determining network or stage coupler, "Bigger isn't all that >> >> > bad."
>> >> > AL CARGPB 33(1/3)www.Team-EM.com
>> >> Thanks Al, I figured for it's function it might be okay, but wanted
>> >> someone to verify this. It is physically larger, but there is >> >> plenty
>> >> of room for it. What is a worst case scenario installing this >> >> larger
>> >> cap?- Hide quoted text -
>> >> - Show quoted text -
>> > Tim,
>> > The concern that some will have, is the rush of current to initially
>> > charge the cap. (Effectively during the first 8 milliseconds.) This >> > is
>> > coming directly from the bridge rectifier of the +5 volt supply
>> > path.
>> > IMO, the time and momentary increase in current will have no impact >> > on
>> > component life or operation. In the long run, (from the 9th
>> > millisecond on) you'll have a cleaner 5 Volt supply.
>> > So there's one opinion.
>> > AL CARGPB 33(1/3)
>> >www.Team-EM.com
>> Unfortunately, I don't agree with Al on this one.
>> Yes, there diefinitely is a huge current inrush at the moment the game >> is
>> turned on. BUT - there is also a huge current inrush every 8.3333 mS >> as
>> well. The cap tends to hold up the voltage longer - providing current
>> during a longer period of time during the rectified AC voltage >> downswing
>> and
>> most the way thru the rectified AC voltage upswing (cap recharges >> during
>> the
>> last part of the rectified AC voltage upswing ONLY).. This gives a
>> flatter
>> DC voltage but, this cuts both ways - better DC voltage but spikey DC
>> current. Due to the fact that the cap stays up higher - the cap has >> less
>> time to recharge resulting in huge current spikes 120 times per >> second.
>> Flatter DC voltage = higher current spikes (which go thru bridge
>> rectifier,
>> caps, etc).
>> More ripple in DC voltage = lower current spikes.
>> Most voltage regulators have a tendency to eliminate some voltage >> ripple
>> during the regulation process so some ripple is ok.
>> I would stay with a value close to the original. 11,700 caps >> originally
>> used were oddities -- closest thing now is 12,000uF. 15,000uF is >> close
>> enough as well.
>> -- Ed- Hide quoted text -
>> - Show quoted text -
> Well Ed, I will repectfully disagree with you. The discharge path is
> through the regulator. Regardless of Cap size, it's only the first
> charge cycle that's the in-rush Demand during the next 90 degrees
> would be the same regardless of the Souce capacitor.
> It's the ten gallon bucket vs. the five gallon one. If all we are
> going to pull out is a quart every 45 and 135 degree and we'll replace
> those quarts on the next cycle at 0 and 180 degrees the either bucket
> will do. The only strain would be the very first charge on power up
> lasting as you said 8.33 mS.
> I don't see any electrical reasons not to, If Tim has the mounting
> real estate and the cap. I would recommend the swap. If he didn't
> have one, I would order the 12000ufd from you.
> AL CARGPB 33(1/3)
>www.Team-EM.com
Ah, a picture is worth a thousand words:http://www.greatplainselectronics.com/downloads/Capcurrent.jpg
Top drawings are voltage, bottom drawings are current.
This drawing represents a half wave rectifier but the current in question is
still represented in this drawing. The half wave circuit in the drawing
would recharge the cap every 16.66mS (based on North American 60Hz power).
A full wave circuit has this current spike every 8.33mS. The full wave
circuit recharges the cap twice as often which results in a current spike
half that of a half wave rectifier -- but this isn't important to the Bally
board unless you have a partially blown bridge rectifier.
The left side of the drawing shows a small capacitor. Voltage has a shorter
hold up time hence longer recharge time on the upswing. This results in a
longer and not as drastic current spike - the positive aspect of a small
cap. But with this smaller cap, you have larger ripple voltage... the
negative aspect of a small cap.
The right side of the drawing shows a somewhat larger capacitor. Voltage
has a longer hold up time hence shorter recharge time on the upswing. This
results in a quick and drastically higher current spike. On the positive
side - with a larger cap, you have smaller ripple voltage.
A large cap whould have a huge current spike during the T1 period.
Depending on the current spike size - this can definitely have a detrimental
affect on the bridge rectifier -- even if the bridge rectifier has a huge 35
amp rating and the averaged load is less than 3 amps.
Some ripple voltage from a rectifier/filter circuit is ok -- as long as the
ripple voltage doesn't cause the overall DC voltage to drop low enough to
start affecting the voltage regulator. As long as the voltage to the
regulator stays high enough - the voltage regulator will eliminate the
effects of ripple voltage on the input.
-- Ed- Hide quoted text -
- Show quoted text -
Ed,
I think this is a very informative thread. It gets into great depth of
one of the electronic principles of linear power supplies. I agree
with all of your statements regarding operation and current surges.
The specified bridge rectifier [VJ248] that supplies this circuit is
rated at 100 amps surge current for a full half wave [8.33mS]. I would
have to think that would be adequate current to supply the discussed
increase in capacitance. [...and probably power most small spot
welders. : ) ]
I've enjoyed our academic banter, yet I feel the real Litmus test will
be whether or not the 4 Amp fuse on the 11.8 V Unreg line blows. If
not, then I think Tim's good to go. If it blows, then it might be
good to have a slew of 12000ufd caps ready to ship. : )
Just thought I'd touch on this for no real reason at all...
A 'fast' 4-amp fuse will take about 10mS to blow at 60 amps, 100mS to blow at about 17 amps and about 300mS to blow at 10 amps....
Now the real question -- what *IS* the real current surge. Seeing as I'm too lazy to calculate this... I guess I'll just let it go. :)
-- Ed
Best Regards,
AL CARGPB 33(1/3)
www.Team-EM.com
.
- References:
- Bally Mata Hari Question- Is bigger, better?
- From: Tim N.
- Re: Bally Mata Hari Question- Is bigger, better?
- From: AL
- Re: Bally Mata Hari Question- Is bigger, better?
- From: Tim N.
- Re: Bally Mata Hari Question- Is bigger, better?
- From: AL
- Re: Bally Mata Hari Question- Is bigger, better?
- From: GPE
- Re: Bally Mata Hari Question- Is bigger, better?
- From: AL
- Re: Bally Mata Hari Question- Is bigger, better?
- From: GPE
- Re: Bally Mata Hari Question- Is bigger, better?
- From: AL
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