Forums

AC spike go pass XFRM and regulator to reset CPU!!??

Started by Rodo April 25, 2008
Hi all,

I have a device that is powered by 240VAC (also works from 120VAC). The AC 
drives the primary of a transformer (with a fuse and a MOV). There is also a 
fan connected to the 240VAC with a switch. The secondary of the transformer 
has a bridge, a large electrolytic cap (1000uF/25v) and an LM7805 regulator. 
There is a smaller cap (10uF/10v and 01uF/25v) at the output of the LM7805. 
Then the 5vdc connects to a PIC.

Almost every time I flip the fan switch a spike shows up at the output of 
the regulator. This is the part that I mostly do not get: even if I 
disconnect the fan and I flip the switch... the spike shows up ... and it is 
a bit larger in amplitude. I grabbed a picture of the spike ... you can see 
it at: http://mysite.verizon.net/rodo/ds0000.bmp

The spike is obviously not always exactly the same. Sometimes is a bigger, 
or smaller more or less oscillations. But the general timming is the same. 
By this I mean I do not have to change the scope's setting to see it.

I tried to: add caps, common mode choke, remove ground (from circuit and 
scope), add larger cap at the output of LM7805, etc., to find why is there a 
spike when there is no load (I removed the fan remember). The ultimate thing 
is that I need to avoid the spike from occuring (with or without load) 
because it is reseting the CPU.

Could someone enlighten me or point me in the right direction please?

Thank you 


Rodo wrote:
> > I have a device that is powered by 240VAC (also works from 120VAC). > The AC drives the primary of a transformer (with a fuse and a MOV). > There is also a fan connected to the 240VAC with a switch. The > secondary of the transformer has a bridge, a large electrolytic cap > (1000uF/25v) and an LM7805 regulator. There is a smaller cap > (10uF/10v and 01uF/25v) at the output of the LM7805. Then the 5vdc > connects to a PIC. > > Almost every time I flip the fan switch a spike shows up at the > output of the regulator. This is the part that I mostly do not get: > even if I disconnect the fan and I flip the switch... the spike > shows up ... and it is a bit larger in amplitude. I grabbed a > picture of the spike ... you can see it at: > http://mysite.verizon.net/rodo/ds0000.bmp
You don't seem to be getting many (in fact zero) answers. I suspect the reason is the same as mine, bafflement. Without the claim that it happens with the fan disconnected I could come up with several attacks, but as it is you seem to just be flipping a totally disconnected switch. -- [mail]: Chuck F (cbfalconer at maineline dot net) [page]: <http://cbfalconer.home.att.net> Try the download section. ** Posted from http://www.teranews.com **
Rodo wrote:

> Hi all, > > I have a device that is powered by 240VAC (also works from 120VAC). The > AC drives the primary of a transformer (with a fuse and a MOV). There > is also a fan connected to the 240VAC with a switch. The secondary of > the transformer has a bridge, a large electrolytic cap (1000uF/25v) and > an LM7805 regulator. There is a smaller cap (10uF/10v and 01uF/25v) at > the output of the LM7805. Then the 5vdc connects to a PIC. > > Almost every time I flip the fan switch a spike shows up at the output > of the regulator. This is the part that I mostly do not get: even if I > disconnect the fan and I flip the switch... the spike shows up ... and > it is a bit larger in amplitude. I grabbed a picture of the spike ... > you can see it at: http://mysite.verizon.net/rodo/ds0000.bmp > > The spike is obviously not always exactly the same. Sometimes is a > bigger, or smaller more or less oscillations. But the general timming > is the same. By this I mean I do not have to change the scope's setting > to see it. > > I tried to: add caps, common mode choke, remove ground (from circuit > and scope), add larger cap at the output of LM7805, etc., to find why > is there a spike when there is no load (I removed the fan remember). > The ultimate thing is that I need to avoid the spike from occuring > (with or without load) because it is reseting the CPU. > > Could someone enlighten me or point me in the right direction please?
IS the fan part of the equipment or is it a desk fan? Inductances can store energy for quite long periods of time and even with the fan disconnetcted, flicking the switch may cause leakages back through the fans input circuitry. Is it only the fan that causes the spike or is there other equipment that causes it too. For all electrical equipment there are now regulations to limit the emissions the equipment produces. There are also immunity requirements on all equipment. When you have eliminated possibilities of direct routes for the interference you may need to consider less direct routes. Is teh circuit adequately shielded? Is the circuit layout such that it minimises teh effect of RF pickup or capacitive pickup from the mains input side? Answering these sorts of questions may give you enough clues. -- ******************************************************************** Paul E. Bennett...............<email://Paul_E.Bennett@topmail.co.uk> Forth based HIDECS Consultancy Mob: +44 (0)7811-639972 Tel: +44 (0)1235-811095 Going Forth Safely ..... EBA. www.electric-boat-association.org.uk.. ********************************************************************
On Apr 26, 10:24=A0am, "Paul E. Bennett" <Paul_E.Benn...@topmail.co.uk>
wrote:
> Rodo wrote: > > Hi all, > > > I have a device that is powered by 240VAC (also works from 120VAC). The > > AC drives the primary of a transformer (with a fuse and a MOV). There > > is also a fan connected to the 240VAC with a switch. The secondary of > > the transformer has a bridge, a large electrolytic cap (1000uF/25v) and > > an LM7805 regulator. There is a smaller cap (10uF/10v and 01uF/25v) at > > the output of the LM7805. Then the 5vdc connects to a PIC. > > > Almost every time I flip the fan switch a spike shows up at the output > > of the regulator. This is the part that I mostly do not get: even if I > > disconnect the fan and I flip the switch... the spike shows up ... and > > it is a bit larger in amplitude. I grabbed a picture of the spike ... > > you can see it at:http://mysite.verizon.net/rodo/ds0000.bmp > > > The spike is obviously not always exactly the same. Sometimes is a > > bigger, or smaller more or less oscillations. But the general timming > > is the same. By this I mean I do not have to change the scope's setting > > to see it. > > > I tried to: add caps, common mode choke, remove ground (from circuit > > and scope), add larger cap at the output of LM7805, etc., to find why > > is there a spike when there is no load (I removed the fan remember). > > The ultimate thing is that I need to avoid the spike from occuring > > (with or without load) because it is reseting the CPU. > > > Could someone enlighten me or point me in the right direction please? > > IS the fan part of the equipment or is it a desk fan? >
Rodo: You might find that a very similar spike on the 0v line. i.e. Just a loop in the scope input to ground. The reason you see the spike is probably because of the EMI filtering around the on/off switch. =3D=3D Rocky =3D=3D
I was thinking about a ground loop with the scope but the circuit is being 
powered by a 110VAC to 220 VAC transformer. I know the grounds are not 
connected because I checked. I wonder if the transformer (110-to-220) is not 
really isolated. I'll have to check this next week.

Someone asked if the fan is part of the equipment. No, it is a totally 
disconnected from the circuit.

Thanks all.

"Rocky" <RobertGush@gmail.com> wrote in message 
news:373bb65d-28c8-483a-ae9c-8a165480ceea@w7g2000hsa.googlegroups.com...
On Apr 26, 10:24 am, "Paul E. Bennett" <Paul_E.Benn...@topmail.co.uk>
wrote:
> Rodo wrote: > > Hi all, > > > I have a device that is powered by 240VAC (also works from 120VAC). The > > AC drives the primary of a transformer (with a fuse and a MOV). There > > is also a fan connected to the 240VAC with a switch. The secondary of > > the transformer has a bridge, a large electrolytic cap (1000uF/25v) and > > an LM7805 regulator. There is a smaller cap (10uF/10v and 01uF/25v) at > > the output of the LM7805. Then the 5vdc connects to a PIC. > > > Almost every time I flip the fan switch a spike shows up at the output > > of the regulator. This is the part that I mostly do not get: even if I > > disconnect the fan and I flip the switch... the spike shows up ... and > > it is a bit larger in amplitude. I grabbed a picture of the spike ... > > you can see it at:http://mysite.verizon.net/rodo/ds0000.bmp > > > The spike is obviously not always exactly the same. Sometimes is a > > bigger, or smaller more or less oscillations. But the general timming > > is the same. By this I mean I do not have to change the scope's setting > > to see it. > > > I tried to: add caps, common mode choke, remove ground (from circuit > > and scope), add larger cap at the output of LM7805, etc., to find why > > is there a spike when there is no load (I removed the fan remember). > > The ultimate thing is that I need to avoid the spike from occuring > > (with or without load) because it is reseting the CPU. > > > Could someone enlighten me or point me in the right direction please? > > IS the fan part of the equipment or is it a desk fan? >
Rodo: You might find that a very similar spike on the 0v line. i.e. Just a loop in the scope input to ground. The reason you see the spike is probably because of the EMI filtering around the on/off switch. == Rocky ==
Rodo wrote:
> Hi all, > > I have a device that is powered by 240VAC (also works from 120VAC). The AC > drives the primary of a transformer (with a fuse and a MOV). There is also a > fan connected to the 240VAC with a switch. The secondary of the transformer > has a bridge, a large electrolytic cap (1000uF/25v) and an LM7805 regulator. > There is a smaller cap (10uF/10v and 01uF/25v) at the output of the LM7805. > Then the 5vdc connects to a PIC. > > Almost every time I flip the fan switch a spike shows up at the output of > the regulator. This is the part that I mostly do not get: even if I > disconnect the fan and I flip the switch... the spike shows up ... and it is > a bit larger in amplitude. I grabbed a picture of the spike ... you can see > it at: http://mysite.verizon.net/rodo/ds0000.bmp > > The spike is obviously not always exactly the same. Sometimes is a bigger, > or smaller more or less oscillations. But the general timming is the same. > By this I mean I do not have to change the scope's setting to see it. > > I tried to: add caps, common mode choke, remove ground (from circuit and > scope), add larger cap at the output of LM7805, etc., to find why is there a > spike when there is no load (I removed the fan remember). The ultimate thing > is that I need to avoid the spike from occuring (with or without load) > because it is reseting the CPU. > > Could someone enlighten me or point me in the right direction please? > > Thank you > >
Can we have some photos of the setup, hosted somewhere and the link posted here?
Rodo wrote:  *** and top-posted - fixed ***
> "Rocky" <RobertGush@gmail.com> wrote > "Paul E. Bennett" <Paul_E.Benn...@topmail.co.uk> wrote: >> Rodo wrote: >> >>> I have a device that is powered by 240VAC (also works from >>> 120VAC). The AC drives the primary of a transformer (with a >>> fuse and a MOV). There is also a fan connected to the 240VAC >>> with a switch. The secondary of the transformer has a bridge, >>> a large electrolytic cap (1000uF/25v) and an LM7805 regulator. >>> There is a smaller cap (10uF/10v and 01uF/25v) at the output >>> of the LM7805. Then the 5vdc connects to a PIC. >>> >>> Almost every time I flip the fan switch a spike shows up at >>> the output of the regulator. This is the part that I mostly >>> do not get: even if I disconnect the fan and I flip the >>> switch... the spike shows up ... and it is a bit larger in >>> amplitude. I grabbed a picture of the spike ... you can >>> see it at:http://mysite.verizon.net/rodo/ds0000.bmp >>> >>> The spike is obviously not always exactly the same. Sometimes >>> is a bigger, or smaller more or less oscillations. But the >>> general timming is the same. By this I mean I do not have to >>> change the scope's setting to see it. >>> >>> I tried to: add caps, common mode choke, remove ground (from >>> circuit and scope), add larger cap at the output of LM7805, >>> etc., to find why is there a spike when there is no load (I >>> removed the fan remember). The ultimate thing is that I need >>> to avoid the spike from occuring (with or without load) >>> because it is reseting the CPU. >>> >>> Could someone enlighten me or point me in the right direction >>> please? >> >> IS the fan part of the equipment or is it a desk fan? > > Rodo: You might find that a very similar spike on the 0v line. > i.e. Just a loop in the scope input to ground. The reason you > see the spike is probably because of the EMI filtering around > the on/off switch. > > I was thinking about a ground loop with the scope but the > circuit is being powered by a 110VAC to 220 VAC transformer. I > know the grounds are not connected because I checked. I wonder > if the transformer (110-to-220) is not really isolated. I'll > have to check this next week. > > Someone asked if the fan is part of the equipment. No, it is a > totally disconnected from the circuit.
Just a quick thought - have you checked the switch in its various positions with an ohmmeter? Have you any other beasts connected to switch terminals? If so, maybe the switch configuration is make before break, rather than the more common break before make. Please do not top-post. Your answer belongs after (or intermixed with) the quoted material to which you reply, after snipping all irrelevant material. I fixed this one. See the following links: <http://www.catb.org/~esr/faqs/smart-questions.html> <http://www.caliburn.nl/topposting.html> <http://www.netmeister.org/news/learn2quote.html> <http://cfaj.freeshell.org/google/> (taming google) -- [mail]: Chuck F (cbfalconer at maineline dot net) [page]: <http://cbfalconer.home.att.net> Try the download section. ** Posted from http://www.teranews.com **
"Rodo" <noway@youwish.com> wrote in message 
news:G2KQj.4106$zw6.2901@trnddc06...
>I was thinking about a ground loop with the scope but the circuit is being >powered by a 110VAC to 220 VAC transformer. I know the grounds are not >connected because I checked. I wonder if the transformer (110-to-220) is >not really isolated. I'll have to check this next week.
Such transformers are usually auto-transformers, i.e. they *don't* isolate - it's just taps on a single winding. Re your spikes while switching a disconnected fan - as Rocky said, check for EMI suppression around the switch. Steve
On Apr 26, 9:24=EF=BF=BDam, "Paul E. Bennett" <Paul_E.Benn...@topmail.co.uk>=

wrote:
> Rodo wrote: > > Hi all, > > > I have a device that is powered by 240VAC (also works from 120VAC). The > > AC drives the primary of a transformer (with a fuse and a MOV). There > > is also a fan connected to the 240VAC with a switch. The secondary of > > the transformer has a bridge, a large electrolytic cap (1000uF/25v) and > > an LM7805 regulator. There is a smaller cap (10uF/10v and 01uF/25v) at > > the output of the LM7805. Then the 5vdc connects to a PIC. > > > Almost every time I flip the fan switch a spike shows up at the output > > of the regulator. This is the part that I mostly do not get: even if I > > disconnect the fan and I flip the switch... the spike shows up ... and > > it is a bit larger in amplitude. I grabbed a picture of the spike ... > > you can see it at:http://mysite.verizon.net/rodo/ds0000.bmp > > > The spike is obviously not always exactly the same. Sometimes is a > > bigger, or smaller more or less oscillations. But the general timming > > is the same. By this I mean I do not have to change the scope's setting > > to see it. > > > I tried to: add caps, common mode choke, remove ground (from circuit > > and scope), add larger cap at the output of LM7805, etc., to find why > > is there a spike when there is no load (I removed the fan remember). > > The ultimate thing is that I need to avoid the spike from occuring > > (with or without load) because it is reseting the CPU. > > > Could someone enlighten me or point me in the right direction please? > > IS the fan part of the equipment or is it a desk fan? > > Inductances can store energy for quite long periods of time and even with > the fan disconnetcted, flicking the switch may cause leakages back > through the fans input circuitry. > > Is it only the fan that causes the spike or is there other equipment that > causes it too. For all electrical equipment there are now regulations to > limit the emissions the equipment produces. There are also immunity > requirements on all equipment. > > When you have eliminated possibilities of direct routes for the > interference you may need to consider less direct routes. Is teh circuit > adequately shielded? Is the circuit layout such that it minimises teh > effect of RF pickup or capacitive pickup from the mains input side? > > Answering these sorts of questions may give you enough clues. > > -- > ******************************************************************** > Paul E. Bennett...............<email://Paul_E.Benn...@topmail.co.uk> > Forth based HIDECS Consultancy > Mob: +44 (0)7811-639972 > Tel: +44 (0)1235-811095 > Going Forth Safely ..... EBA.www.electric-boat-association.org.uk.. > ********************************************************************- Hide=
quoted text -
> > - Show quoted text -
You need a line filter on the transformer primary, you should allways fit one anyway.
You're right. I felt rather silly connecting the scope probe to ground 
(where the probe ground was) but I did and voila! I got a spike at 0v. This 
is pretty weird to me ... not a power guy. Someone suggested a line filter? 
I was looking around the net and found several configurations ... I'll have 
to read some more to figure this stuff out.

Thanks


"Rocky" <RobertGush@gmail.com> wrote in message 
news:373bb65d-28c8-483a-ae9c-8a165480ceea@w7g2000hsa.googlegroups.com...
On Apr 26, 10:24 am, "Paul E. Bennett" <Paul_E.Benn...@topmail.co.uk>
wrote:
> Rodo wrote: > > Hi all, > > > I have a device that is powered by 240VAC (also works from 120VAC). The > > AC drives the primary of a transformer (with a fuse and a MOV). There > > is also a fan connected to the 240VAC with a switch. The secondary of > > the transformer has a bridge, a large electrolytic cap (1000uF/25v) and > > an LM7805 regulator. There is a smaller cap (10uF/10v and 01uF/25v) at > > the output of the LM7805. Then the 5vdc connects to a PIC. > > > Almost every time I flip the fan switch a spike shows up at the output > > of the regulator. This is the part that I mostly do not get: even if I > > disconnect the fan and I flip the switch... the spike shows up ... and > > it is a bit larger in amplitude. I grabbed a picture of the spike ... > > you can see it at:http://mysite.verizon.net/rodo/ds0000.bmp > > > The spike is obviously not always exactly the same. Sometimes is a > > bigger, or smaller more or less oscillations. But the general timming > > is the same. By this I mean I do not have to change the scope's setting > > to see it. > > > I tried to: add caps, common mode choke, remove ground (from circuit > > and scope), add larger cap at the output of LM7805, etc., to find why > > is there a spike when there is no load (I removed the fan remember). > > The ultimate thing is that I need to avoid the spike from occuring > > (with or without load) because it is reseting the CPU. > > > Could someone enlighten me or point me in the right direction please? > > IS the fan part of the equipment or is it a desk fan? >
Rodo: You might find that a very similar spike on the 0v line. i.e. Just a loop in the scope input to ground. The reason you see the spike is probably because of the EMI filtering around the on/off switch. == Rocky ==