16A Mitre Saw With 14A Transformer ????

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  #1  
Old 07-12-07, 03:40 PM
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16A Mitre Saw With 14A Transformer ????

Hi all, sorry if I'm not in the right place with this post but I could do with some help. I have an 110v dewalt mitre saw and today I decided to buy my own site transformer to go with it, so I can give back the one I’ve been borrowing off my mate for the past year. Anyway I spotted one on eBay, a 3KVA one which is what I was told to get and the guy lived just up the road, so I bought it. Anyway it wasn't till I got it home that I realised that the 2 socket outlets are 14A but my saw is rated 16A. So the question is , is it safe to use it with my saw, I'm guessing that the saw never pulls 16A under normal operation, also is it possible to have the plugs changed on the transformer for 16A ones. I apologize for my utter ignorance in these matters and hope that someone will take pity on me.

Cheers

Rich
 
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Old 07-12-07, 04:18 PM
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Originally Posted by ijakk View Post
I have an 110v dewalt mitre saw and today I decided to buy my own site transformer to go with it, so I can give back the one Iíve been borrowing off my mate for the past year. Anyway I spotted one on eBay, a 3KVA one which is what I was told to get and the guy lived just up the road, so I bought it. Anyway it wasn't till I got it home that I realised that the 2 socket outlets are 14A but my saw is rated 16A. So the question is , is it safe to use it with my saw, I'm guessing that the saw never pulls 16A under normal operation, also is it possible to have the plugs changed on the transformer for 16A ones. Rich
Rich
You sound like you live across the great pond and not in the USA.
Is the input voltage to the transformer 240 volts? I must assume 120 volts is not available. You should not try to use the 14 amps sockets. The will get hot
and probably melt over time. What you have is a 3000 watt transformer
which has a full load capacity of 12.5 amps at 240 volts. On the secondary you have 2 120 outlets rated at 12.5 amps(total 3000 watts). You transformer may be able to withstand the load for a short time. Maybe you should take it to your "mate" and get your money back.
 
  #3  
Old 07-12-07, 04:25 PM
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Which model DeWalt do you have?

This will be a good thread for me. I'll be moving to Papua New Guinea (Aussie power config) next week for two years and am having a 3KW transformer shipped there for me to use my wife's 120V 1400W Vitamix blender.

The duty cycle on humans using a miter saw is usually very low. Far more time is spent on fit than actual cutting. Without even running numbers, which I will when I know which saw you have, I'm guessing you're fine.
 
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Old 07-12-07, 04:30 PM
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I am also going to assume that you live in an area where the "normal" voltage is 240 volts. According to my chart a 3kVA transformer that "steps down from 240 volts to 120 volts will supply 25 amperes at 120 volts. This is certainly adaquate for a tool that is rated at 16 amperes.

As for the receptacles...you probably will want to change them to the higher rated ones although the truth be told your saw will rarely be drawing the maximum amperage. The 16 amperes maximum draw of your saw is only about a 15% overload on the receptacle rating and no overload on the transformer itself, assuming a 240 volt input.

I'd say that you are probably okay.
 
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Old 07-13-07, 12:17 AM
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Thanks

Hi guys, sorry I didn't realise this was a mostly american site. Yes I live in England and on site we tend to use cordless or 110v instead of the standard 240v, 110v is considered to be safer. I was rather puzzled by this site transformer because I could not find a unit anywhere else that had 14A sockets, so I peeled the label off, that stated 14A and low and behold under neath was the standard BS4343 16A socket, so although I feel rather dumb right now, I still can't understand why someone would go to the trouble of stick 14A labels on both sockets. The saw is a dewalt DW707 by the way.
Many thanks for all your replies.

Rich
 
  #6  
Old 07-13-07, 08:23 AM
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I have used Dewalt miter saws made for the U.S. market. They work fine on a 15 or twenty amp circuit even sharing it with other loads. Except in a production environment they are usually used for a very short time each time they are used. My saw is rated 13 amp. Note also it is AC-DC so frequency should not be a factor.
 
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Old 07-13-07, 10:02 AM
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Originally Posted by furd View Post
I am also going to assume that you live in an area where the "normal" voltage is 240 volts. According to my chart a 3kVA transformer that "steps down from 240 volts to 120 volts will supply 25 amperes at 120 volts. This is certainly adaquate for a tool that is rated at 16 amperes.
I'd say that you are probably okay.
Furd,
You are missing the point. If he had only one socket your comment would be right. He has two sockets. The transformer load is divided between the two.
You don't have a 25 amps supply, you have 2 - 12.5 supplies. There is a difference. The saw draws 16 amps. Since the cut is only a short time, it probably will work. You could parallel the secondary winding if that's possible and then you would have a 25 amps supply.
 
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Old 07-13-07, 11:38 AM
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How do you know this? I didn't see a schematic posted for his transformer to show that the receptacles were not in parallel. The ones on my 3KW transformer are and I can use the full ampacity out of any of them.
 
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Old 07-13-07, 12:30 PM
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MAC is absolutely correct. There is no reason to suspect that the transformer in question is a 1:1 ratio with a center-tapped secondary. Such a transformer would be rather uncommon whereas a transformer with a 2:1 ratio and having no center-tapped windings is quite common.

I made a logical assumption that the two "sockets" were simply wired in parallel and that there were two of them simply for convenience. For all I know it could be a standard duplex receptacle.
 
  #10  
Old 07-14-07, 11:27 AM
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Originally Posted by MAC702 View Post
How do you know this? I didn't see a schematic posted for his transformer to show that the receptacles were not in parallel. The ones on my 3KW transformer are and I can use the full ampacity out of any of them.
Originally Posted by furd
MAC is absolutely correct. There is no reason to suspect that the transformer in question is a 1:1 ratio with a center-tapped secondary.

OK. I will buy that. Why doesn't the [quote] symbol highlight the post?
 
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Old 07-14-07, 11:37 AM
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Wareagle Asked: "OK. I will buy that. Why doesn't the [quote] symbol highlight the post?"

That's because the site owners are paranoid about security and think even limited use of BB codes could be dangerous. At this point it seems they are firmly locked into their beliefs and nothing is likely to change. Ironic since I am almost sure I have seen ads with videos permitted here. <G>
 
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