Wiring up PSU

I'm quite new to the forums (but a long time reader), and have decided to post a question I had regarding the electronics for Reprap printer I am currently building.

I currently reside in Japan, where line voltage is 100 V (50 Hz; I'm on the east side of the country).

I have sourced an appropriate PSU, but had a question regarding the wiring.

Japanese mains do not come with ground, and only have (non-polarized) live and neutral. Since there is no polarization, I assume it does not matter which wire I put into the L(ive) and N(eutral) terminals on the PSU.

However, most Japanese mains do not come with ground (and my house is no exception). Is it safe to use a PSU with no ground connection? I tried looking for this info on the forums, but came up empty handed.

The back of the PSU has your typical screw down type connections; my first instinct was to use ring or U-shaped crimp terminal connectors, but looking at a few specifications on Japanese sites, I noticed the following:

DC12V480W and under / DC24V960W and under

Obviously, these will be fine for the DC side, but what about the mains line? I was not aware that such limitations actually existed (I always assumed that as long as the crimp terminal/insulation could handle the current, that it would be fine to use).

Any help regarding these issues would be greatly appreciated.

For AC current going into a switching PSU it shouldn't matter - having ground is more of a safety issue than anything else. Here in the US most houses are wired with hot (live) and common (neutral) and ground, with ground connected to the earth via a conducting pipe at the circuit breaker box where the mains connection enters the house. Grounding provides a separate return path (other than through your body) with lower resistance should a hot connection come loose and come in contact with the metal housing or other exposed conducting parts. Also the input power may only have a fuse on the hot wire so you might want to check the polarity and make sure that live goes to live. Hot connections coming loose can happen for a number of reasons but usually don't last for long as they involve something melting or exploding inside the PSU. Hopefully that won't happen to you!

I found that generic PSUs may sometimes not match their specifications or advertised rating, particularly when it comes to the 12V rails. This caused me a lot of lost time and frustration trying to figure out why it took so long to reach temperature.

Edited 1 time(s). Last edit at 09/11/2013 02:26PM by papergeek.

Thanks for the reply; I figured that it was really only a safety issue (I've had some experience with wiring mains line in Canada, but there was always a ground; I've never had to wire mains in Japan where there is no ground and the mains is not polarized).

I know that in Canada/US, looking at a socket, live is on the right and neutral is on the left, but I'll do some more digging to see if it is the same in Japan (it probably is, but just to be sure...)

Hopefully the PSU won't give me too much trouble. The one I purchased was through a Japanese supplier here (sorry, website is only in Japanese):

[akon.jp]

I got the AK320W-SC-12, which is rated at 12V and 25A.

(Here's a quick Google translate, if anyone is actually interested)

[translate.google.ca]

I'm hoping that the PSU should be fine, since it's not your typical eBay PSU. Comments are welcome!

Edit: Does anyone have any comment about the ring terminals? Or are most people just twisting the strands of wire together and hooking it up directly to the PSU (is this recommended for mains line?)

Edited 1 time(s). Last edit at 09/11/2013 07:22PM by Darkblade48.

Simple test is to use a multimeter and measure against ground (a metallic waterpipe ideally but any conducting floor should give you at least a partial voltage reading). The neutral side should give you nothing. Of course you want to be careful when inserting a multimeter probe into a live electrical outlet! Note that touching the exposed metal of the probe while inserted in the live side of the outlet while grounded will give you a nasty shock.

320W sounds insufficient despite how they rate 25A at 12V. If it doesn't provide enough current you'll find that you can't get the bed and nozzle up to temperature in a reasonable time (if at all).

This may be helpful for you: AC power plugs on wikipedia. It sounds like the unpolarized outlets are a bit out of date. Generally the larger slot on a polarized plug is the larger one but the orientation of the outlet may vary, so your neutral may be the one on the left (or not if the installer put the outlet in upside-down).

I guess testing the outlet is the only way to know for certain; I figured as much.

I've always heard that you haven't really worked with electricity until you've been shocked at least once (I hope this doesn't become my first time)...

Is there any reason why you think 320W won't be sufficient? From what I understand, most people aim to have > 20A power supply at 12V (at least 240W power).

I've looked at the Wikipedia article on AC power plugs (Googled everything before posting on these forums); unfortunately, non-grounded, non-polarized plugs in Japan are the norm, especially in older apartments (such as mine).

I assume you meant to say that my neutral might be on the right (if it was reversed); I thought neutral on the left (polarized side with larger slot) was the norm in Canada/US.


Edit regarding forked/ring crimp terminals:

I have a set of blue coloured fork crimp terminals; they are rated for wires from 1.5 - 2.5 square mm (wires with diameter 1.4 - 1.8 mm). Furthermore, they are rated at DC12V 200W and lower; these are clearly suitable for the DC end, but what about the live/neutral/ground ends (connecting to AC)? Clearly the mains line will be 100V, but I figure the current drawn won't exceed that of the crimp terminals.

Edited 1 time(s). Last edit at 09/12/2013 08:31AM by Darkblade48.

Neutral on the left (as you are facing the plug and the grounding pin is on the bottom) is normal here in the US. It's not uncommon (as in my house, built in 1972) for the electrician to install the outlets upside down with the grounding pin on the top. So without polarization it's good to check.

Your PSU will either work or not work - there's no harm in trying it. I believe that vendors (especially generic whitelabel vendors in China) may sometimes overstate their current capacity because they figure that nobody can possibly be using all that current and if they are, how are they going to know our PSU is to blame???

I have a Prusa i3 with a Magma hot end connected to RAMPS 1.4 electronics. I haven't measured current consumption but the heated bed is supposed to draw 11A at 12V and the nozzle heater should draw 6A. I started out with a generic 400W PSU that claimed to provide 20A on the 12V rail. I connected both the mainboard 12V and what is usually the "high current" 12V (from a 4-pin or 6-pin Molex connector with yellow and black wires) and everything worked ok but I could never reach the full temperature with both heated bed and nozzle, even after waiting an hour or more.

So yes, if you actually have a PSU that supplies 20A as stated you should be fine. If the manufacturer is lying about the capacity you may end up with insufficient current.

The Magma comes with a fan and if the fan is blowing directly on the nozzle, it may be nearly impossible to get higher temperatures, but after switching to an Antec Basiq 500W power supply I did not have any problems, and suddenly my time to heat the bed dropped from 30 minutes to 2 minutes. So I am quite positive the 400W power supply was simply not performing as rated.

In my opinion it's worth soldering after crimping particularly for heater connections. 2 square mm wire is approximately equivalent to AWG14 (1.63mm diameter) which should be sufficient (I'm using stranded AWG14 for my RAMPS to heated bed connection, which is probably overkill). That is also a commonly used gauge (per wire) for small appliances and PC power cords, so should be sufficient.

Guess I'll have to check the electricity socket then! My apartment isn't quite as old as yours, built in 1977, but still, you never know.

I'll give the PSU a shot; hopefully it should be OK since it's a Japanese company (probably with parts and labour all from China!).

I have a similar setup (Prusa i3, heated bed, but with J-head Mk V hot end and RAMPS 1.4), so hopefully all goes well.

And thanks for the tip regarding the crimped connectors; I will probably solder anyway, since I only have a non-racheting crimper, and can't really trust its performance.