Re: Bally Mata Hari Question- Is bigger, better?


"AL" <AL@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

.

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