DC12V 12A car window motor - what spec for a 220V PSU?

[jim hardy]

I'll stop there, because the recorded AC voltages are unrelated to your theoretical projections.

That's too much AC . I don't know what's happening. Myself i'd suspect the meter is doing something that i do not expect of meters.

I'll try on my charger.

 

[marcophys]

That's too much AC . I don't know what's happening. Myself i'd suspect the meter is doing something that i do not expect of meters.

I've metered it again, on both fast and normal charge (without capacitor across output).
in both cases AC is showing slightly more than double the DC.

Re the capacitor.
I've found a couple of 50V 0.1 µF capacitors.
I also came across an RBV 602 bridge rectifier
https://www.digchip.com/datasheets/parts/datasheet/139/RBV602-pdf.php
http://pdf1.alldatasheet.com/datasheet-pdf/view/38177/SANKEN/RBV-602.html

 

[marcophys]

I fitted the RBV 602 to the output - the two centre pins.

The two outer pins (marked + - ) delivered similar readings... AC just more than double the DC.
I presume that this confirms that something is amiss with my meter.

Anyway, having got the rectifier... I'll see how it works with the motor.

 

[jim hardy]

Your tenacity is to be admired !

 

[marcophys]

Your tenacity is to be admired !

Thanks Jim.
But to be fair, it was alarm & confusion that was the driver.
Seeing AC everywhere on my meter.
I needed this confirming, not only for this project, but for future metering.

It seems that you are right - my AC meter shows just over double the DC value, even after passing through the bridge rectifier.
Anyway...

I wired the RBV to the charger output, and then wired the capacitor across the rectified output.
My thinking was that, either way, the RBV would likely clean up the voltage further.
Placing the capacitor last was simply the easiest for testing.
Perhaps the capacitor is best placed in the charger, where you suggested the lamp position.

RBV 602 Results

If 4V DC is seen at the output
... 3V DC is seen after the capacitor
... 2V DC is seen at the motor (10m 1.5 sq mm cable)​

The RBV gets hot
The capacitor remains cool

The RBV therefore requires mounting on aluminium.

Motor

• Quieter
• It sounds better
• It operates down to 7 rpm (1.7Kg load)

This looks like it is the limit, due to a tight spot, either in the gearing or drive shaft alignment.

Ideal Component Positioning

1.8k Resistor
This can be positioned on the voltage control board, and wired across the socket outlet.

680 µF 200V Capacitor
Currently located after the RBV rectifier.

Options

• Pre charger rectifier (Jims lamp photo)
• Post-charger rectifier (IE. the traditional output)
• Post RBV rectifier

I'm going to try it at pre-charger rectifier.
It is a convenient location point, and it should tidy the supply to the rectifier.

 

[marcophys]

Ha!
No... it was a failure.
(Damn... I spent an age creating the wiring art)

Result
The moment that I switched the motor on... I knew.

The first thing was that it wouldn't start - it needed more power.
... then the sound.

I had another capacitor, so I quickly placed it after the RBV.
This confirmed that the capacitor should be the last component.
... meaning that it, and the RBV can be mounted on the motor switch control panel.

Q. Is there any reason to keep the capacitor mounted in the charger case?
It's nicely mounted, so it can stay... if we think that it must be helping somewhat.

 

[jim hardy]

Whoah ! You wired your capacitor IN SERIES with the transformer return lead. That'll blow it up.
EDIT
oops i missed one wire
i still think you have it on AC side so that's why it'll blow..

It has to go in PARALLEL and AFTER the rectifier.

 

[marcophys]

Well... I wired it as per your photo:

"Trial and error is the approach for this one. See if a 40 watt 12 V lamp on secondary behave noticeably different from a 40watt 240 volt lamp on primary ?
To avoid rectifier drop he could connect it here"

It shows 12V AC with dimmer feed... so it is in parallel.

 

[marcophys]

I have changed the wiring of the internal capacitor.
It is now wired across the output -ve and the +ve entry to the fuse, similar to Jim's recent suggestion above.

Result
This worked.

I then wired in the 2nd capacitor after the RBV.
The motor was slowed to 6.5 rpm.

I then disconnected the 2nd capacitor, and the motor would not run.
Re-connected it... and the motor ran.

From this it would appear that the motor benefits from the 2nd capacitor.
Perhaps this just means that the 680 µF 200V Capacitor should be increased.

Note
These speeds are at the absolute minimum.
The motor actually 'cut-out' momentarily after stalling for a few seconds..

Perhaps there is a thermal overload within the motor casing.
There seems to have been no damage - it runs fine now.

I'm only running at 'stall speed' for test purposes.
... and it is proving a useful tactic.

The Problem (with an internal capacitor)
The DC voltage output is 20V DC.

I placed a 240V 40W lamp across the output... it was still 19.5V.
My first thought was that this would prevent the battery charger from being used as such.
However, I then thought about the dimmed voltage.

Without any additional switches or wiring within the charger
... I can now dim the voltage down to whatever is desired.
This should mean that I can use the charger for both 12V & 6V batteries.
... a definite 'side effect' win

The RBV could be mounted within the charger chassis, but I'm now of a mind to locate it on the 'motor switch control panel'.

On that I'll pause.
I need to sort out all my heat sinks, and see how best to do it.

Overall
... my failure to mount the capacitor correctly has added to our knowledge.
As usual, it has raised another question... as to 'what is the ideal capacitor value'?

But these are details.
I now need to physically wrap up the project - get everything securely and safely mounted.

I'll then take some photos, so that the system can be seen

 

[Tom.G]

Perhaps this just means that the 680 µF 200V Capacitor should be increased.

Depends on what you are after. The higher the capacitance the higher the average DC voltage under load (within reason). Adding the external RBV rectifier just subtracts about 1.5V delivered to the motor, hence the lower speed.

Knowing the @jim hardy expertise with graphics and detailed explanations, perhaps he can come up with some waveforms and average versus peak voltages. My quick mental calcs indicate to reduce the ripple voltage at the motor to 1V would need roughly 10 000uF with a 1A load on the charger output.

@jim hardy : Sorry to put you an the spot here, but the conversation seemed to need steering to a better understanding of the phenomena... and I'm otherwise occupied for a bit.

p.s. The different fwd/rev motor speeds may be that the brushes are rotated with respect to the field windings, often a design choice.

 

[marcophys]

The different fwd/rev motor speeds may be that the brushes are rotated with respect to the field windings, often a design choice.

Ah... so we are not completely in the dark

Wrapping up what we have achieved

Motor control panel
As you can see... I fitted the resistor onto it's heat dissipating aluminium bracket
... and then fitted the bracket to it's natural place, only...

The plug flex would tend to lay on the resistor, which is not great.
It means that it will need a flex guide, if I keep the resistor in this position.
(it's a typical prototyping error... you can never think of everything, until it's done, and then...)

Battery Charger - Motor PSU
This shows the mounting of the 1st capacitor, and wiring into the output

Motor Switch Panel
I hear what you say Tom, re the RBV.
Subjectively, the motor seemed to run better - I swapped it in and out a few times.
Anyway I kept it, and mounted it on an aluminium heat sink, with an alloy plate on top, to further improve heat dissipation.
Heat paste was also used.

The 2nd capacitor was kept because, again subjectively, the motor seemed to run marginally better.
The capacitors run cool... I could barely feel any warmth
... as a result, I've tie-wrapped it in place... it was simply convenient.

The 5A fuse is between the RBV +ve and the main switch.

I need to tidy the exposed connectors... but it's pretty much there.

Last main job is to bridge the switches.

Very pleased with it.

 

[jim hardy]

I'm a bit confused as to what we have now.

Is RBV a bridge rectifier
Where is it installed and connected ?

What is the "Second capacitor" ?
680 or 0.1 ?
Where is it connected ?
Where is the 0.1 connected ?

The Problem (with an internal capacitor)
The DC voltage output is 20V DC.

That must be with the 680 connected AFTER the bridge on its DC side ?
Will dimmer not drive it lower ?

Can you mark up that sketch & photo from post 88 ? It was great !

old jim

 

[jim hardy]

I really don't think some ripple will hurt the motor and it'll help it make torque at low speed. That's how electric drills work.

I need confidence that the schematic in my mind is the schematic we actually have .

How's it working ? I get conflicting thoughts

The Problem (with an internal capacitor)
The DC voltage output is 20V DC.

Without any additional switches or wiring within the charger
... I can now dim the voltage down to whatever is desired.

in same post

 

[marcophys]

I'm a bit confused as to what we have now.

Understood.

It's the universal difficulty in documenting change.
... the current status as compared to previous status (and maybe in the same post, a mention of the planned mods).
Of course, the writer knows what's happening, but as for everybody else...

Is RBV a bridge rectifier

RBV 602 bridge rectifier
https://www.digchip.com/datasheets/parts/datasheet/139/RBV602-pdf.php
http://pdf1.alldatasheet.com/datasheet-pdf/view/38177/SANKEN/RBV-602.html

Where is it installed and connected ?

Mounted on an aluminium heat sink, with an alloy plate on top, to further improve heat dissipation.
Heat paste was also used.

The two centre pins are AC - directly fed by the input connector at bottom.
Red left passes thru the fuse to the primary motor switch.

What is the "Second capacitor" ?

SAMXON 680 µF 200v LP (M) 85 deg (has polarity)

Where is the 0.1 connected ?

Place a small capacitor, maybe 0.1 or .0.01 uf , in series with your meter's red lead and see whether that affects its reporting of AC volts.

This related to my meter reading AC at a DC outlet.
I haven't done this test yet

Can you mark up that sketch & photo from post 88 ? It was great !

Yes I will.

The funny story (funny to me) is that I should already have drawn a digital diagram.
I sketched it out first, and was unsure how the heat sink/rectifier worked.
Then I thought oo... maybe I can just upload it as an image... I'll just pop it into Gimp.
... and that was it.
I spent ages trying different filters & mods.
A new drawing would have only taken ten minutes ​

I will draft the diagram... and then perhaps the community can explain why it does what it does.
At least... I now know it uses a bridge rectifier.
This should help.

 

[jim hardy]

Thanks man, you are a good explainer of things !

 

[marcophys]

Absaar 108 NE/D2 12V Battery Charger
With added capacitor for motor load

Image Notes
The image seems to have been re-scaled.
Even opening in a new tab fails to show the image at full size.

The only unreadable element is the capacitor spec:
SAMXON 680 µF 200v LP (M) 85 deg

Charger Notes
Cable cores are solid 1.5mm D from the secondary winding, and the ammeter circuit.
Multicore:- central switch to rectifier, rectifier -ve output, fuse +ve output
(The capacitor leads used are solid core)

Two Core To Switch
The middle secondary output in grey, is of two solid twisted cores of 1.5mm D.
It connects to the Lo charge switch contact.

Is this simply an interruption in the windings
... the core then returning to the coil to make more turns?

Fuse
Absaar never replied to my email questioning the fuse... so we know nothing about it.
I've marked it as a thermal fuse... it was a reasonable guess.

Switch
There was some resistance across the switch contacts.
This was cleaned up with contact cleaner, and now, both contacts are just 1Ω.

 

[jim hardy]

It's a tapped secondary winding. Low voltage switch setting uses part of the turns high voltage setting uses them all.
So red is one end of secondary, looks like blue is the other end and grey(looks purple on my screen)

is someplace in between .

Your big cap looks to be in exact place i would have put it.

I've marked it as a thermal fuse... it was a reasonable guess.

If the cap unscrews and there's a fuse inside then it's a fuse.
More llkely it's a thermal circuit breaker that's rather slow to open . Its job is to protect the wires and rectifier if it can.
Battery chargers use very stout rectifiers that can withstand a brief short circuit and even survive when somebody hooks up the battery backwards.
I doubt your RBV602 is as robust
from the datasheet you linked

i read that as 40 amps will likely kill it in a second.Nice work.

I'm hunting for my old battery charger and DMM now.

old jim

 

[jim hardy]

My raggedy old charger and el-cheapo DMM gave the following:

Charger alone:
13.02 VDC ,
switching to AC reads 4.45
so unfiltered it has roughly 34% AC content.

With 100 uf across output:
17.52 VDC,
switching to AC reads 0.05
so the 100 uf is an effective filter.
It both raises the DC level to sinewave peak and removes the AC content.

That's why i was surprised by your earlier AC readings of 29 and 44 volts, they were so different from what i expected..

I presume that this confirms that something is amiss with my meter.

Perchance is yours an analog meter ?

If it's a DMM , i noticed something about mine that i'd just always accepted as a "DMM Peculiarity".
When i switched from DC to AC my meter jumped up to about double the DC reading then drifted back down to stable reading over a matter of seconds...
That's because selecting the AC range switches in an internal capacitor to block the DC , and that capacitor takes a while to charge.
During that charge interval the meter is experiencing current at its input namely the internal capacitor's charging current, which it interprets as AC .
One gets so accustomed to that 'oh, it's just another digital meter quirk' he accepts it and forgets to forewarn newbies.
So ---
Solving your meter's AC anomaly might be as simple as waiting for your DMM to settle. Takes a few seconds.Your enthusiasm is both heartwarming and infectious.
Keep on having fun,

old jim

 

[marcophys]

Perchance is yours an analog meter ?

No... it's digital.

Solving your meter anomaly might be as simple as waiting for your DMM to settle. Takes a few seconds.

Sadly, also no!.
I've just measured the charger output on Lo (with capacitor as per drawing) = 39V AC - 17.8V DC
It remains stable within 0.2V for a minute.

On Hi the output is 44.5V AC - 20.3V DC

Note... It's Sunday evening:
Mains supply is fluctuating between 230V - 234V AC (over 2 seconds).
IE. It cycles up and down.

Just a thought... it would be interesting to monitor the mains supply over the course of a day.
However, regardless; we can see why for testing, one needs a regulated mains supply.​

Therefore my DMM is consistently more than doubling the DC voltage, when set to AC.

My DMM

Notice the bar that I resoldered... it had parted.
It leads to the 10A connector.

I have just now resoldered the connections to the board.
I don't think that this should affect the normal volts readings, but maybe the heat (during failure) has caused problems.

The thing is... it seems to work for everything other than AC voltage on a DC circuit.
What to do?
Perhaps it has a capacitor that is failing.

After reassembly, it is no different.
I just have to live with it for the time being.

 

[jim hardy]

That's fine.
For a sanity check try a car battery or 9V battery , something you know has no AC even connected to it.

That'll say conclusively whether Mr DMM is ailing.

 

[marcophys]

Ha!... good idea.
Just checked a 1.3V DC battery... it shows a lovely 2.4V AC.

I guess that confirms it

 

[jim hardy]

I guess that confirms it

Dont you love it when those little confusion factors drop one by one ?

That's troubleshooting... what's left is the truth.

 

[marcophys]

Don't you love it when those little confusion factors drop one by one ?
That's troubleshooting... what's left is the truth.

Yes... if only the search for truth was not a dangerous area of interest.​

However, confusion does have additional benefits, as it stimulates discovery in areas that otherwise might have been missed.

I gained knowledge of my DMM, which is very useful for future metering.
... but the error threw up the question over how the DC voltage was being created, leading to investigation of bridge rectifiers, and then the new wiring diagram.

I do believe that by 'having everything' (particularly early on in adulthood), this condition removes the absolute requirement for innovation, and tends to preclude the development of an innovative mindset.
... and the self belief that no engineering problem is unsolvable.

Of course, once you are hard wired to solve problems... it would be nice to have all the machinery and test equipment at your disposal
... but even with a dodgy DMM, a stopwatch, eyes, and ears, we have created a very useful tool.

It would be nice to have full knowledge of it - perhaps only achievable with an oscilloscope.
Tom raised the issue of the RVB 602 being surplus to requirement.
Clearly the system ran fine without it.
However, with it, the motor ran marginally better at slowest speeds.

I don't know why... I simply observed this.
Similarly the 2nd capacitor.

But at that point, we have reached the limits of my testing capabilities.
I'm fine about that.

It's hard to arrive at a decision to 'stop working' on a project... but it must be done.
I can use the mind trick, and say to myself... we'll have another look later.

So that really is it.
Time to get on with other pressing matters that have been put on hold.
We can reconvene when the next issue arises.

Thanks to everybody for being there.

 

[jim hardy]

Your big capacitor has one other benefit for you. It absorbs transients from the transformer thereby protecting your RVB 50 volt bridge rectifier.

Below is unnecessary, not showing off just want to be thorough. Might as well learn all we can from an experimental oroject.

Recall i said above that battery chargers use robust rectifiers, capable of withstanding short circuits and reverse connected batteries.
They're also capable of withstanding surprising overvoltage.

When you unplug a battery charger from the wall it suddenly interrupts current through the transformer primary.
How much is that current at instant of disconnect depends on where in the sine wave the plug and receptacle break contact .
Size of the "inductive kick" or "spike" you'll get depends on how much was the current at that instant, ie how close to sinewave peak was the current when contact broke.
If the battery is still connected no sweat at all, the battery absorbs the "spike" and you have graceful shutdown.
If the battery is NOT still connected then the rectifier will be subjected to whatever "spike" the transformer produces. Something must absorb the energy.
That's why i say "Battery charger rectifiers are more robust than your garden variety bridges."
I think they are an avalanche type that survives reasonable overvoltage .

To demonstrate that effect,
yesterday while tinkering with my old raggedy charger and DMM
i connected a 10 uf motor run capacitor across output.
AC and DC voltages were about the same with 10uf as with 100 uf , about 13 and 4.5

Then to show the effect of "Inductive Kick" i unplugged the charger power cord.
The meter jumped to 110VDC and bled down over a few seconds.
Tried it again, got only 20 VDC

About 10 'unplugs' showed random DC voltages, many in the 70 to 100 volt range and some showing no spike at all..
That's not surprising because a sine wave statistically spends most of its time near peak . Sin 45 degrees is 0.71 so it spends half its time above 70%. .

I repeated with the 100 uf and never saw above 20 volts if that many, i forget...

What does that mean ? It means your charger could make a spike that exceeds your RBV bridge's 50 volt rating.
But your 680 uf capacitor is surely big enough to absorb the energy and protect the little RBV.

Energy=1/2 CV²
My 6 amp charger put energy = 1/2 X (10 X 10^-6farads X 110volts² ) = 0.0605 Joules into that ten microfarad capacitor.
That many Joules into 100 uf would be 35 volts if they all went in, some get lost in the wires and transformer...
and into 680 uf it would be only 13 volts.

So your capacitor will prolong the life of your RBV bridge.

I formed the habit years ago of always unplugging the charger's power cord BEFORE disconnecting the battery just to make life easier on my charger's internal rectifier.

There's your trivia for today...

Applying "The Basics" to everyday life is really fun.

old jim

 

[marcophys]

That's fantastic information Jim.
I really appreciate the sharing of that knowledge.
I will never again disconnect the battery before switching off the battery charger.

For the motor control, we now have two capacitors - one in the charger, the other across the RBV DC output.
As it is currently wired (on the motor switch control panel), the RBV and 2nd capacitor is prior to the motor on/off switch.

Theoretically... am I correct in assuming that, ideally the motor switch should be prior to the RBV and capacitor.
... the switch would then cut the current to the RBV, capacitor, and motor, thus allowing the motor to bleed away the residual current?

Note: I have heard you, vis a vis the protection provided by the capacitors... it's just a theoretical question (that can anyway be enacted).

 

[jim hardy]

Theoretically... am I correct in assuming that, ideally the motor switch should be prior to the RBV and capacitor.
... the switch would then cut the current to the RBV, capacitor, and motor, thus allowing the motor to bleed away the residual current?

That connection will be the most gentle one for power off.
But at power on there's substantial current into the second capacitor. Well, i say substantial but with just 13 volts and 680 uf it's hardly high power.

In interest of being thorough
connecting them in order capacitor switch bridge motor gives gentle startup AND gentle shutdown. No sudden charging of capacitor on switch closure, and on switch opening the bridge absorbs inductive spike from motor. But you should include a bleed-down resistor or lamp (12 volt LED will do) across the last capacitor.

I can tell you're sort of a perfectionist. Take that as a compliment. Your wiring is neat and clean looking.
I suffer a similar malady - frustrated perfectionism. We're the type who get a project built and working then go buy all new parts and start all over because it didn't come out looking perfect.

Keep having fun. Enjoy applying basic physics to everyday situations.

old jim

 

[Asymptotic]

But you should include a bleed-down resistor or lamp (12 volt LED will do) across the last capacitor.

Good point.

Going back several posts, the question was how to size the output capacitor.

The violet line added to Jim's waveform is DC voltage with an output capacitor added. If only a little bit of capacitance is added then that line dives deeper towards 0V, and adding more flattens it out towards more nearly connecting each voltage peak. Ripple factor is 1/(4*sqrt(3)*f*c*r). Line frequency f is 50 Hz. Lowering r (resistance), in other words increasing the load, increases ripple, and increasing c (capacitance) decreases ripple. However, no matter how much capacitance is added there will always be ripple, and after a certain point adding more becomes a matter of diminishing returns. Although it doesn't much matter in this case, a whopping huge capacitance makes motor response to (dimmer) speed control setpoint changes sloppy, and (if the motor remains connected to the capacitor on power down) instead of coasting quickly to a stop it'll decelerate more slowly as the capacitor discharges.

680 uF is, in my opinion, a good compromise value in a circuit such as this. The most I've used is 56,400 uF (twelve 4700uF caps in parallel), but under different circumstances; in a 700V DC link supply for a 11 kW servo application that required very fast accel.

Your project does all the things you need it to do, it looks good, and I believe you've wrung out all the performance you are liable to get. Better pick up a different DVM, though.

 

[marcophys]

connecting them in order capacitor switch bridge motor gives gentle startup AND gentle shutdown. No sudden charging of capacitor on switch closure, and on switch opening the bridge absorbs inductive spike from motor. But you should include a bleed-down resistor or lamp (12 volt LED will do) across the last capacitor.

That's the info I was looking for... how it should be wired.
I've drafted the wiring diagram as it currently stands, and added a bridge to the polarity switches.

the question was how to size the output capacitor

This was also the info I was looking for.
It explains everything to me.
I now understand why one side of the bridge rectifier was showing 6V... it was missing the lower wave.
Also the explanation of what the capacitor is doing, and what in fact the ripple is... it's all clear now.

What a relief!

Apart from Jim's recommended mods... here is the completed panel, and current wiring diagram:

 

[marcophys]

Here it is with an LED added and the diagram updated.
The LED glows while the motor is drawing current, and is just slightly illuminated when live.

... but what's also interesting (and put a smile on my face)
The LED varies the glow according to how hard the motor is working.
If the motor is close to stalling, it glows bright... and brightest if the motor actually stalls.

 

[jim hardy]

@Asymptotic

Nice Job !

@Marcop
here's an approximate way to estimate ripple on a capacitor. Proper calculation requires calculus but this back of the envelope will get you close enough for home projects.

During that bleed down period between peaks, current to your load comes from the capacitor. In power supply filter applications think of the capacitor as a short term battery or reservoir for charge..

Current I into or out of a capacitor is I = C X (Δvolts / Δtime)
and ripple is Δvolts between rectified sinewave peaks.

Where you are is 50 hz so downstream of your rectifier there's a peak every 1 / 100th of a second, 10 milliseconds.

Rearrange I = C X (Δvolts / Δtime) to get Δvolts and you get Δvolts = Δtime X I / C

Now at 1 amp and 680 uf and ten milliseconds i get Δvolts = 0.01sec X 1amp / 680X10^-6Farads = 14.7 volts

so your 680 won't run the motor very long
but is sure helps your dimmer meet holding current..

Really ripple won't be the full 14.7 volts because the actual Δt will be somewhat less than a complete half cycle.

Here's an addition to Asymptotic's great picture:

Asymptotic showed a large capacitor, i showed a small one.
For audio you need a huge one to reduce hum.
You just need enough to keep the triac "Latched", ie meet its holding current requirement.

Knowing slope, Δvolts / Δtime, you could calculate the point where the lines depart. And you could estimate the point where they'll rejoin.
You can use that to build a very fast "Loss of AC detector" . I once had to detect loss of 60 hz AC within twelve milliseconds (for a computer) and that's the approach we used.

sorry for boring everybody

have fun

old jim