Capacitor question

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reelshows

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Today i received the replacements for my start and run capacitors in my akai 1700. They are 1/2 the physical size as the originals. The originals were metal, the new ones are plastic. The sizes and volt ratings are the same, except one should be a .5uf and the replacement is a .68uf. The 2uf is so small that it won't fit in the bracket, but i can strap it with a nylon tie.

I believe they will work, just wanted some other opinions before i solder and can't return.
 
We're talking electrolytic caps? They have gotten better and smaller over the years so don't worry about the physical differences.
 
Yup, that's the deal. I agree with Sweetbeats. Due to the advances in diaelectrics (the non-conducting material between the plates of the cap), caps have gotten smaller with better drift characteristics as well.
 
The 0.68uF instead of 0.5uF might be an issue. Best to have the same capacitance or you might have weaker motor torque.

If you cant get exactly the right figure , you could always use two or more capacitors in a parallel or series arrangement.
 
I'm glad you chimed in, Tim...those are things I NEVER can remember though I know it is pretty important to keep motor caps to stock values...so for the good of the order, if you wire two caps in series it sums the capacitance values (i.e. two 1uF caps in series will net a 2uF circuit), and wiring in parallel halves the capacitance seen by the system? :confused:
 
Good info, these have no polarity, would that make a difference in series? It's been along time for me since ATR-A school, USN. I never was good theory man anyway.

These were sent by allied electronics as equal replacements. I had to go thru an electric motor repair place and they ordered them for
me. Do you think they will work. Both checked bad, actually the 2uf checked 5 or 6uf. The.5 was actually totally bad.

The motor in the 1700 would not turn. You could start it by hand, but if there was a load on it it would stop.
 
reelshows said:
Good info, these have no polarity, would that make a difference in series?
Click to expand...
If they're electrolytics, they will have a polarity. It's crucial that this is right. Worst case, they may explode if it's not (seriously).
 
sweetbeats said:
I'm glad you chimed in, Tim...those are things I NEVER can remember though I know it is pretty important to keep motor caps to stock values...so for the good of the order, if you wire two caps in series it sums the capacitance values (i.e. two 1uF caps in series will net a 2uF circuit), and wiring in parallel halves the capacitance seen by the system? :confused:
Click to expand...

You got the principle right, Cory but it's the other way round. Series reduces the value and parallel increases it at at least with capacitance. There's an equation for it something like:
1/C total = 1/ C1 + C2 and another for the other way round but I'm away from the workshop so cant locate it at present. It'll be on the www somewhere.

Cheers Tim
 
Tim Gillett said:
You got the principle right, Cory but it's the other way round. Series reduces the value and parallel increases it at at least with capacitance. There's an equation for it something like:
1/C total = 1/ C1 + C2 and another for the other way round but I'm away from the workshop so cant locate it at present. It'll be on the www somewhere.

Cheers Tim
Click to expand...

Series is 1/C total = 1/C1 + 1/C2 + 1/C3 etc...
Parallel is C total = C1 + C2 + C3 etc...
By the way inductance is just the opposite.
VP
 
reciprocal of sums of reciprocals

R = 1/(1/r1 + 1/r2 + 1/rN) for parallel resistances

C = 1/(1/c1 + 1/c2 + 1/cN) for series capacitance

Inductors are more complex. That is to say that if they are not interacting then the resistance formulas work. but if they are interaction (e.g. a transformer or 2 or mor coils who see each others magnetic field) then youu need a new formula.

See http://en.wikipedia.org/wiki/Series_and_parallel_circuits

Regards, Ethan
 
jpmorris said:
If they're electrolytics, they will have a polarity. It's crucial that this is right. Worst case, they may explode if it's not (seriously).
Click to expand...


Actually, there are some electrolytics capacitors that are bipolar (unpolarized) ;)

But as jpmorris said, if they are polarized and that you place them backward, they may explode in your face and spread paper everywhere in the room where you are... I've seen it a couple of times and it's very impressive to see how much material is in there :eek:
 
Tim, Ethan, VP, thanks for the formulas. ;)

Yep...plenty of bipolar electrolytics around.
 
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Hey I know those formulas! :) I just finished a unit on electricity in physics. Same formula except we used it to find Equivalent Resistance.
 
samth3mancgp said:
Hey I know those formulas! :) I just finished a unit on electricity in physics. Same formula except we used it to find Equivalent Resistance.
Click to expand...

I'm sure you did :)

These are applications of Kirchhoff's laws to specific cases. They have been around since about 1857.

--Ethan
 
"Summing" capas in paralel is straight forward and easy to "understand".
BUT!
...due to the nature of the device hanging capacitors in series makes me feel uncomfortable. Also, I guess it depends on application. Also, I don't understand it completely and never had enough patience to dig through and that's another reason for why I personally would avoid it.

When it comes to connecting ELECTROLYTIC capacitors in series - I would not do this unless I REALLY REALLY have to and there's no other way around.
I had one time situation when I simply had no workaround available, as I needed 8uF electrolytic cap rated at 600V !, so I had to use pair of 16uF/450V caps that I've found, and then I had to spend a day reading the damn "theory" and spent a day in the "lab" testing, calculating resistors values and testing again just to fix that thing. Not fun at all :mad:
I have some crappy demontration photos here: http://www.mzentertainment.com/pics/test_equipment/emc_801/dr_zee_workshop_emc_801_inside.jpg, there you can see that big yellow old cap that is later replaced with two black caps and resistors in parallel with each cap, (the project page here: http://www.mzentertainment.com/studio_workshop_test_equipment_emc_801.html )

here are couple of links I've booked in the past:
http://www.bhc.co.uk/literature.htm , there click on "TD001" doc.

http://www.nmr.mgh.harvard.edu/~reese/electrolytics/ , scroll down to "caps in series" part.
 
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These are Metallized Polypropy:axial capacitors they are not polarized. I called the supplier and they said that the .68uf was well within the 10% + or - of the .5uf orig. He said that they are electrolytics and very few are not polarized. I wanted to make sure before they exploded. I've seen it before.

I installed them today, and the 1700 is playing fine. I have to clean the drive, find out where those two strips of wood go that fell out and put it back together. I ordered a belt, but it hasn't arrived. I may wait and see if they are able to find one.

Now I have a sony 260 tore apart that may have the same problem, the motor runs slow under a load. I just got it this week. Going to look at a Sansui 7000 tomorrow.

Thanks for everyone's input. I actually remember some of that theory stuff, been a long time.

By the way, the motor start cap is 2uf and about 1/4 the size of the orig. It would not work in the bracket, so I had to do some riggin to get it in a good spot. Sure felt good to see that motor spin right up.
 
I think my brain turned to mush reading this thread.:eek: Never taken any electrical or electronics courses. I know what the components are and understand the values, but the construction and formulas have me lost.:D
 
Tim Gillett said:
Actually it's only high schooll physics.
Click to expand...
There's no such thing as "high school physycs".

There's such thing as "introductory level of knowledge".

"High school knowledge" is a form of introductory level of knowledge, the primary properties of which are: absence of challenge, extreme passion and short memory.
High school knowledge is NOT tied to the age of an individual.
:)
 
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