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volt meter wiring

 
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rgrrbt



Joined: 08 Jan 2011
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PostLink    Posted: Sat Jan 08, 2011 4:36 am    Post subject: volt meter wiring Reply with quote


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Kal, in the wiring diagram posted on The Electric Brewery site, you indicate both 14 gauge Hot A and Hot B going into the back of the volt meter. How did you wire this given the pin socket that is included with the volt meter appears to be 22-24 gauge?
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kal
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PostLink    Posted: Sat Jan 08, 2011 9:56 pm    Post subject: Reply with quote

14 ga is pretty small. It may fit. You can cut off some of the strands to make it fit if you want, or solder on a little piece of solid core 22ga wire and put on some really small heat shrink tubing to cover up the solder point to ensure you don't get shorts. That's what I did.

Here's a pic:



Kal

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crush



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PostLink    Posted: Sun Jan 09, 2011 12:14 am    Post subject: Reply with quote

[Deleted: double post]

Last edited by crush on Sun Jan 09, 2011 12:28 am; edited 1 time in total
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crush



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PostLink    Posted: Sun Jan 09, 2011 12:27 am    Post subject: Reply with quote

I've been wondering why we need two transformers, and if someone can explain exactly what is isolation and why it's necessary here. I'm wondering why the variable transformers themselves don't provide isolation, but having 2 doorbell transformers does?

Which device is it that need isolating, the voltmeter or ammeter? I'm hoping to power many low current 12v devices, so I hope they can all come from the same power supply and just use one extra supply for the "rogue" unit. Smile

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crush



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PostLink    Posted: Sun Jan 09, 2011 12:30 am    Post subject: Reply with quote

Can't we use 22 gauge for the meter - surely the current drawn is in milliamps?
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kal
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PostLink    Posted: Sun Jan 09, 2011 2:26 am    Post subject: Reply with quote

crush wrote:
I've been wondering why we need two transformers, and if someone can explain exactly what is isolation and why it's necessary here. I'm wondering why the variable transformers themselves don't provide isolation, but having 2 doorbell transformers does?

Which device is it that need isolating, the voltmeter or ammeter? I'm hoping to power many low current 12v devices, so I hope they can all come from the same power supply and just use one extra supply for the "rogue" unit. Smile


One of the AC inputs on the volt meter is tied to the DC ground so separate power supplies are needed.

crush wrote:
Can't we use 22 gauge for the meter - surely the current drawn is in milliamps?


You make a good point. You can. I've changed the picture. It can all be 22 ga.

Kal

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crush



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Location: Telemark, Norway


PostLink    Posted: Sat Feb 05, 2011 1:41 pm    Post subject: Reply with quote

kal wrote:
crush wrote:
I've been wondering why we need two transformers, and if someone can explain exactly what is isolation and why it's necessary here. I'm wondering why the variable transformers themselves don't provide isolation, but having 2 doorbell transformers does?

Which device is it that need isolating, the voltmeter or ammeter? I'm hoping to power many low current 12v devices, so I hope they can all come from the same power supply and just use one extra supply for the "rogue" unit. Smile


One of the AC inputs on the volt meter is tied to the DC ground so separate power supplies are needed.


After some research and thinking, I believe I see why isolation is needed and how this is provided by the transformer.

I think it's something like this: with the 120v AC and DC ground wired together in the voltmeter, any return path to AC will allow 120v to flow through the DC side of the circuit. When a transformer is used, there is no return path, since the input / output coils are entirely separate and there is no path to complete a 120v circuit. Using a switched power supply would not work, since there is an electrical connection between the output and the input, allowing 120v to flow.

But what I don't understand is why two transformers are needed. Can someone correct my thinking and explain exactly what happens with one transformer that causes the circuit to blow?

Thanks,
mat.

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crush



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PostLink    Posted: Mon Feb 07, 2011 2:05 pm    Post subject: Reply with quote

I just noticed on my ammeter that the instructions also say that this has the dc ground wired to a 230v input, so both the ammeter and the voltmeter have this feature. So now I see why both need isolating. In principle, it's possible to have just one transformer, but you have to be 100% certain that the the 230v that is tied to the dc ground is the same polarity on both meters. If they are opposite polairty, then a circuit is formed and 230v will flow through the dc side of the circuit. So, it's simplest just to have two transformers where this cannot happen.
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kal
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PostLink    Posted: Mon Feb 07, 2011 2:10 pm    Post subject: Reply with quote

crush wrote:
So, it's simplest just to have two transformers where this cannot happen.

Hence the reason I used two transformers. Wink

Kal

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crush



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PostLink    Posted: Mon Feb 07, 2011 3:07 pm    Post subject: Reply with quote

kal wrote:
crush wrote:
So, it's simplest just to have two transformers where this cannot happen.

Hence the reason I used two transformers. Wink

Kal

Hehe! Yes, simplest is best. I just wanted to understand exactly why it was necessary.
I'll be using two transformers also. Safely using just one requires opening up both meters to see which AC input is tied to ground in each, and making sure both of those have the same polarity. Too much hassle!

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kal
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PostLink    Posted: Mon Feb 07, 2011 3:18 pm    Post subject: Reply with quote

Yup. Maybe not too much hassle for someone who knows what they're doing but for my instructions I have to go the 'safe' way since not all meters may be the same and I didn't want to have to give all sorts of complicated instructions for people to just save $10. I also did not want to assume that people would be buying the exact same meters as me.

You also don't want to have to re-think the wiring if every you decide to replace a part. The system should be build somewhat generically to minimize reliances between parts.

Kal

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