No Galvanic Isolation - High Risk? 120VDC Power Supply
Started by kcarring · · 15 posts · last reply 2 February 2011
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#1 ·
In an electronics forum I tried to open the topic of of taking a diode bridge and rectifying 120AC directly to 120VDC with capacitive smoothing for use as a power supply for a 60 plate electrolyser. My thoughts were that I needed the same number of volts on the AC side as the DC side, why involve a bulky, costly, and hot transformer, if unneccesary. My thread was immediately shut down due to the discussion of No Galvanic Isolation. The forum is very picky, anyone speaking of overunity, HHO, free energy, or anyone displaying any questionable circuitry with any home made components gets deleted.
Is it really that dangerous? I see many others doing it and now I'm very curious. If it is truly that dangerous, I won't bother.
Thanks -
#2 ·
rectifying 120VAC would give around 168VDC -
#3 ·
Ok. At a peak, correct? And your thoughts on the danger? I don't want to be doing something completely stupid and was pretty surprised to be "shut down" - the topic.. completely. I'm wondering if not employing galvanic isolation is as dangerous as implied.rave154 wrote:
rectifying 120VAC would give around 168VDC -
#4 ·
Very Dangerous
The problem with not using an isolation transformer is the very real danger of getting yourself or someone else electrocuted. One side of your normal AC 120 volt circuit is tied to ground. If you use a bridge directly off the 120 volt AC circuit then all of your circuit will be hot in reference to ground. Both your plus and minus side of the bridge is now above ground by about 70 volts or so. If you come into contact with any part of your circuit and ground at the same time you will now complete the circuit back to ground with a pulsating DC current going through your body. AC passing through your body causes the muscles to contract and may make it hard for you to turn loose. DC passing through your body burns a pathway causing potentially serious damage. Under the right circumstances either AC or DC can easily kill you. It only takes a few milliamperes to do. Always use an isolation transformer if working with Line powered AC devices.
Be careful, Carroll -
#5 ·
Thanks! No need to electrocute myself!citfta wrote:
The problem with not using an isolation transformer is the very real danger of getting yourself or someone else electrocuted. One side of your normal AC 120 volt circuit is tied to ground. If you use a bridge directly off the 120 volt AC circuit then all of your circuit will be hot in reference to ground. Both your plus and minus side of the bridge is now above ground by about 70 volts or so. If you come into contact with any part of your circuit and ground at the same time you will now complete the circuit back to ground with a pulsating DC current going through your body. AC passing through your body causes the muscles to contract and may make it hard for you to turn loose. DC passing through your body burns a pathway causing potentially serious damage. Under the right circumstances either AC or DC can easily kill you. It only takes a few milliamperes to do. Always use an isolation transformer if working with Line powered AC devices.
Be careful, Carroll -
#6 ·
Carroll,citfta wrote:
Always use an isolation transformer if working with Line powered AC devices. Be careful, Carroll
Do you think this might do the trick?
YouTube - Isolation Transformer? What do you think?
Thanks,
Kyle -
#7 ·
Look at this
Kyle I think you would be better off with something like this one I found on Ebay.
ISOLATION TRANSFORMER POWERTEC USA P/N 02-0010 PRI 120V - eBay (item 220700656500 end time Feb-20-11 14:28:23 PST)
I didn't see anything in the video you showed that tells us what the inputs and outputs are. The link I have here is for a transformer that will handle 100 watts. Which means you will get about 160 volts after you rectify the AC to Dc and about 625 milliamps of current. If you tell me what kind of current and voltage you are looking for I'll tell you what you need to be looking for. Hope this helps.
Carroll -
#8 ·
Actually, that is an incorrect statement.citfta wrote:
If you use a bridge directly off the 120 volt AC circuit
then all of your circuit will be hot in reference to ground.
Both your plus and minus side of the bridge is now
above ground by about 70 volts or so.
First,
the most efficient usage of the available
dual-polar voltage swings will always be
four diodes in a full-wave bridge configuration.
That is why all current electronic equipment I've seen
uses it since people stopped using tubes as rectifiers...
(Yeah, I'm that old)
As one of the leads IS referenced to ground (Neutral),
the minus side will ONLY be the diode's junction drop higher than that.
Measure any of your transformer-less TV supplies...
The other will have "Peaks" as high as noted,
but the RMS value remains near the same.
The "Peak" value does have merit
to this conversation still though,
because of rectification and smothing
with a bank of electrlytic capacitors.
The amount of cells MUST account
for the TOTAL voltage sustained
under the load presented by the cell.
Factor for at least high 160's for voltage !
The first plate on the negative side
would be a diode's voltage drop from neutral.
Each progressive plate away from it
would then become more hazardous.
Had the topic have been using L1 AND L2,
meaning pole-1 and pole-2 of the electric service.
Then your answer would have been completely correct.
The mean-average voltage would be
swung from both sides of neutral.
In both cases, and in all equipment,
having a safely grounded enclosure
in case of failure a is paramount !
even the L1+L2 scenario is no different
than the 220-VAC clothes dryer you use...
I hope this helps. -
#9 ·
Sorry but I don't agree
To WeThePeople,
Sorry but I don't agree. Your conclusion would be correct if the hot side of the 120 AC never went below ground. But for half the cycle the hot side is negative in reference to the neutral side. Therefore the negative of the bridge will be about 60-65 volts negative in relation to the neutral. I may have misled you when I said all the circuit would be hot. I meant in reference to ground all the circuit will be live or will still bite if you touch it and ground at the same time. When the first transformerless TVs came out there were a lot of techs that blew up their scope leads when they tried to connect the ground lead of the probe to the negative of the circuits like they had always done before. Since the chassis of most scopes is connected to ground they created a short from the negative of the supply back to the neutral which was grounded. We learned real quick we had to start using an isolation transformer on our scope or cut off the ground pin of the power cord. I am also an old dog with many years of experience in making mistakes like that.
Hope that explains it correctly.
Carroll -
#10 ·
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#11 ·
Dc- Dc isolation?
This, however appears to be DC-DC isolation? Could one bridge rectify to DC - THEN do isolation, leaving only a small encased portion of the project, at risk? -
#12 ·
Maybe I should clarify what I am doing here.
I intend of using 120 vdc across a series of electrolyser anodes, so on one end you have - and many neutral plates later, you have +.
The exact number of neutral plates will be determined by the average potential available, given the power source SO when I revamp my electrolyser I need first determine what I have to work with.
Ultimately you will have between 1.75 and 2.3 v per cell. If smoothing were employed it would be ultimate to have that ripple vary from the above two figures, or close to.
I don't know much about voltage regulation, though I do understand capacitive smoothing.
The natural "pulse train" is a good thing, the variance.
If you like I can share with you the circuit I have, as purchased by Eagle Research, but I have to redo it, draw it myself as I probably shouldnt just scan the book and publish it.
Please view this video as it is nearly identical to what I am talking about.
This is what most guys are doing, and this is what I am concerned with, an identical situation... is this safe or not...?
YouTube - HHO 120V CELL DRIVER -
#13 ·
Why not use a capacitive transformer instead if you are using voltage below mains? No inductors and very low loss.
Capacitive Battery Charger, incl. Capacitive Transformer | www.eagle-research.com
YouTube - DIY Capacitive Battery Charger
DIY Capacitive Battery Charger -
#14 ·
schematic
This video, goes over, in detail: the schematic to the previous video:
YouTube - HHO 120V SCHEMATIC -
#15 ·
Thanks. This may be what George does, and possibly I am not looking at all of this correctly. He states that he has avoided the use of a heavy, costly transformer. Which is what i want to do, if it can be done 100% safely.SilverToGold wrote:
Why not use a capacitive transformer instead if you are using voltage below mains? No inductors and very low loss.
Capacitive Battery Charger, incl. Capacitive Transformer | www.eagle-research.com
YouTube - DIY Capacitive Battery Charger
Thanks Again.
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