Relais and big CAP

Status
Not open for further replies.
T

TKS

New Member
Hi all,

I have build module for in my car.

But it uses a huge cap (10.000uF)

Sow i cant let it stay connected because it will drain the car battery.

How much amps relais do i need on the pcb to be able to turn it on and off?
(together with the hole device)

Regards,

Tks

p.d. i now have a 10Amps 230VAC but i guess that if switching inductance it should be allot less. problem is that the cap sparks.. sow the relais will suffer not??
 
Why don't you just use an on/off switch? WHat is this module exactly? (Don't tell me it's something to improve the electrical performance of your car and will let your car accelerate faster. If it is, don't even bother with the module.).

10uF is not that big a cap...unless you mean 10mF. But what is the leakage on the capacitor? Is it large enough warrant all this?

Relays (whe properly rated) only suffer when they are breaking currents. If they are just sitting there staying on, they can take almost anything. THe power/current/voltage required to switch the relay is in the relay's datasheet.

Now about properly rated relays...Does 230VAC, 10A mean that the relay can handle 230VAC at 10A? Do you now know what is required to switch the relay? It has to be 12VDC since that's what car batteries are. Since the relay is VAC, then the DC current it can switch/break will be a LOT less, possibly even less than 1A. And because you are switching an inductive load, the current it can handle is even less. So it probably won't work with your application.

You were talking about a capacitor, but now you are talking about an inductive load...what is that all about?
 
Last edited:
10uF is huge? The 20uF 35 volts capacitors I have are the size of a dime long and 1/3rd that wide..

How is a cap going to drain the car battery?
What do you mean your cap is sparking? You need to describe the circuit you're using better.
 
I have a feeling he means a 1F Cap. They are used in High end Audio Amps for cars...Or maybe its 10,000uF.

I dont see how a cap will ruin the battery. It only takes a couple mS to charge and its current is equal to V/R (if R exists, if not then its a short).

By switching inductance he means generated EMF by the relay coil. When power is removed a Huge Voltage is induced and then released. A Reverse Biased Diode (1N914) should do. (I couldnt for the life of me, Remember the other Diode-1N9004 or something)
 
Last edited:
I see, so he is confusing the inductance of the coil used to activate the relay, with the inductance of the load (of which there is none) that is connected to the primary power contacts of the relay?

He says he thinks switching inductance will reduce his current rating, which makes no sense since the current rating is for the primary power contacts and not the coil. The inductance of the relay coil is not the same as an inductance attached across the relay power terminals.
 
I dont see how a cap will ruin the battery. It only takes a couple mS to charge and its current is equal to V/R
Click to expand...
Unless it is one of the silly ones you see in the "sound system" section of your local consumer electroncs stores. I kid you not, they sell "capacitors" for auto-audiophiles that have built in flashing lights and a voltmeter to make it look cool and charge you a ridiculous price for it. Maybe this is simular to what the Op has:
**broken link removed**
 
Last edited:
There's a little too much speculation going on =) wait till the original poster actually says something.
 
I think he means 10mF of 10,000:mu:F.

I wish people wouldn't use '.' instead of a ',', m for :mu:F is also confusing because the m could either stand for milli or micro.
 
Hero999 said:
I wish people wouldn't use '.' instead of a ',', m for :mu:F is also confusing because the m could either stand for milli or micro.
Click to expand...

Don't be so provincial! different countries use different standards, this is a worldwide forum, for many members English isn't a first language (and may not even be their second one!).
 
Hero999 said:
I think he means 10mF of 10,000:mu:F.

I wish people wouldn't use '.' instead of a ',', m for :mu:F is also confusing because the m could either stand for milli or micro.
Click to expand...
I use M for Mega, m for milli and u for micro.
 
SI says that m is milli and u is micro, and M is mega. I could also be mistaken, but . is a decimal point everywhere, wheras a space and , are used depending on area. Of course, those prefixes only hold true if it's an SI unit...

kft, doesnt make any sense lol.

10.000uF could be a typo. We should ask TKS what he uses for a decimal point.
 
Last edited:
plus that is the point of the SI thou divisor, if he really does mean 10,000uF, why not write it as 10mF. Just has bad as Farnell writing some of their pF capacitance in mF... ie A PAIN!!!
 
Last edited:
I got a feeling he just copied the text straight off the cap, so it's either a typo, or a really small uber-precision capacitor lol
 
I have a vague recollection that, years ago, mF (meaning micro Farad) was used in lieu of uF
 
ljcox said:
I have a vague recollection that, years ago, mF (meaning micro Farad) was used in lieu of uF
Click to expand...

I think that was in America, who alwasy tend to be a little different to the rest of the world!

And of course it's not 'u' it's the greek letter 'mu' :mu:
 
Mfd was the full abreviation not MF. MF would still logically be mili farads. I have a few capacitors I got in a grab bag that are marked in MFd's
 
Nigel Goodwin said:
And of course it's not 'u' it's the greek letter 'mu' :mu:
Click to expand...

I know but I did not know how to insert a :mu: but your post has shown the light.

But how do you insert Pi? I tried "pi" inside colons but that did not work.
 
Last edited:
ljcox said:
I know but I did not know how to insert a :mu: but your post has shown the light.

But how do you insert Pi? I tried "pi" inside colons but that did not work.
Click to expand...

You don't, it's not a graphic that the administrator has added (he added five extra ones, they are listed under smilies)
 
Thanks Nigel, but where are they listed?

I looked in the "Post icons" below but could not see any.

When I clicked on the Smile, all it did was to insert a smile icon.
 
Status
Not open for further replies.

Similar threads

D
Audio out Mod Cap?
Replies
2
Views
1K
Tony Stewart
X
  • Solved
my question is about big capacitor and it's parasitic inductance.
2
Replies
21
Views
5K
JimB
G
  • Question
Need for these capacitors and resistors
Replies
12
Views
3K
ChrisP58
  • Question
Digital potentiometer problem and questions
Replies
7
Views
2K
GH Crash
  • Question
What is the waveform and frequency of the lcr t4 device when testing the capacitor?
Replies
7
Views
2K
danadak
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…