Hi Ken................................ ...........th,
The third diagram on right will work just fine.
Make up a heater to be a little 'warmer' than you think, then duplicate it.
No problemo.
You've just "completed a parallel circuit". L.
ps. After finishing your heater, try wrapping it around your arm to test for temp.
You'll soon know if it's way too hot. hahahahahaha..
pps. I'd forgotten all about my 'alligator/crocodile clip' trick/post, errr, way of getting the correct temp.
ppps. A PWM (Pulse Width Modulation), unit will let you control the temp more accurately. Cost about $25 odd?? Not sure, as I make my own for lot less, as you know.
Would you like one? Only cost ya $40....
Hi Ken................................ ...........th,
The third diagram on right will work just fine.
Make up a heater to be a little 'warmer' than you think, then duplicate it.
No problemo.
You've just "completed a parallel circuit". L.
ps. After finishing your heater, try wrapping it around your arm to test for temp.
You'll soon know if it's way too hot. hahahahahaha..
pps. I'd forgotten all about my 'alligator/crocodile clip' trick/post, errr, way of getting the correct temp.
ppps. A PWM (Pulse Width Modulation), unit will let you control the temp more accurately. Cost about $25 odd?? Not sure, as I make my own for lot less, as you know.
Would you like one? Only cost ya $40....
Hiya Laurie, long time no see! I've been waiting for you to pop up in Skype!!!
Thanks for the info mate. I have some pots I can try. Hopefully they won't be the Carbon core ones. They are from a busted monitor.
I am attempting to make a single control box for 4 items all run through pots. ED80 heater, Guidescope Heater, Toucam fan, and a spare for whatever.
Sorry, as Laurie says, the middle and right diagrams are both the same, parellel, and will do the same thing, only the right one uses more wire ;-). Use either.
Youll find the heater gets much hotter off the tube, without the tube to soak up the heat.
Ken, I would recommend you post here your final wiring topology including the
individual lengths of the two segments of nichrome before using the system
in the field and we can double-check it for you.
The math is very important from a safety view point. For example, there is
concern you could exceed the rating of the power supply, the very worse case
scenario in the type of environment you are operating being lethal, so please
run it by us first.
We'd hate to see you suddenly stop posting.
You absolutely must also run an inline fuse. We can advise on final value once
you advise on lengths and power supply.
Sorry, as Laurie says, the middle and right diagrams are both the same, parellel, and will do the same thing, only the right one uses more wire ;-). Use either.
Youll find the heater gets much hotter off the tube, without the tube to soak up the heat.
Thanks Fred.
Bit hard to test length on the OTA, but I'll try work something out
Ken, I would recommend you post here your final wiring topology including the
individual lengths of the two segments of nichrome before using the system
in the field and we can double-check it for you.
The math is very important from a safety view point. For example, there is
concern you could exceed the rating of the power supply, the very worse case
scenario in the type of environment you are operating being lethal, so please
run it by us first.
We'd hate to see you suddenly stop posting.
You absolutely must also run an inline fuse. We can advise on final value once
you advise on lengths and power supply.
Best Regards
Gary Kopff B.E. (Elec. Eng.)
Thanks Gary. Once I know lengths etc I'll let you check it
I am confused about the Fuses. I looked in my shed and I can only find one fuse and fuse holder. It is 250v 6amp.
How many fuses would I need, what ratings, and where would they go. On each heater line? or just for the power supply?
Hi Ken,
You will only need one fuse. Suggest you go to Jaycar and get something like
Cat No. SZ2015 which is a 3AG In-line fuse holder (set you back all of $1.15)
and buy an appropriate 3AG quick blow glass encapsulated fuse (35 cents or twice that
if you want a spare). Since the power supply you mentioned is rated to only 1A,
a 1A fuse would be a good place to start (Jaycar Cat No. SF2190). However,
what I would do is compute an appropriate value fuse based on the lengths
of nichrome you end up using in parallel and the output voltage of the
power supply. We can assist in that simple calculation.
Solder the fuse holder in-line with the positive lead coming from the positive
output of the power supply. Make sure you insulate the connections.
I would recommend a short segment of heat shrink tubing which you slide over
the wire and out of the way before soldering, then slide over the joint after
soldering. If you have a real industrial hot-air gun, use it to shrink the heat-shrink.
A hair drier usually is not hot enough. If you are very careful, you can also
do it over a stove hot-plate. Most heat-shrink halves its diameter on contraction (so
called 2:1), so buy a diameter appropriate for the wire. Just try sliding it
over the wire in the store.
The fuse will serve several purposes. For example, a back-of-the-envelope
calculation hints that for the two lengths of wire you might be using in
parallel and given the rated voltage of the power supply you mentioned, you might be exceeding its rating current output, which is something you don't
want to do. Secondly, in the event of an inadvertent short circuit, maybe not
today but at sometime in the future when the system has undergone a certain
amount of wear and tear, you don't want to run the risk of burning yourself
or damaging the scope. The fuse will hopefully limit the current sometime
before such an eventuality.
Readers of this thread who use 12V lead-acid or gel cell batteries should
not drop your guard either. Alwys use appropriate short circuit protection,
such as a fuse, as such power sources can deliver very large amounts of current,
and in the case of some battery technologies, such as car batteries, in very
short amounts of time.
Ken,
That is an excellent diagram. Showing off your artistic skills again huh? j/k.
One question tho? I'm not sure if you said you already had a multimeter, digital or otherwise (insert 'moving coil, needle type' here), to measure the RESISTANCE of the heaters? Most Important.
This value is needed to calculate the CURRENT drawn.
(JIC.....To measure, simply connect the meter leads to each lead of each heater separately. Hopefully both heaters will be about the same reading in OHMS). Alternatively, a digital multimeter can be bought for around $15. It should be capable of measuring up to 10 AMPS DC. Most Jaycar ones are.
This way, you can measure the current drawn by one or both heaters & the fan.
Most computer fans draw ~200 mA or .2 of an AMP.
Connect the meter in series with the fuse in the +ve line.
If the reading is close to or more than 1 AMP for one heater, then I would go looking for a larger capacity power supply. Say, a 3 to 5 AMP one.
Keep us informed as that way, we'll know you're still kicking.
Regards, Laurie..
Looks good, but you now need to determine the individual
lengths of the two pieces of nichrome plus let us know what the
rated current draw of the fan is. Most of those 80mm box PC
fans draw about 0.08A at 12V. This will then allow us to determine the
total current draw so that will will then know whether it is higher than
the 1A rating of the power supply. If it is not, you will either need to
increase the length of the nichrome segments or add one or
more current limiting resistors in series with the nichrome wire.
Do you also happen to know whether the power supply is 13.5V DC or AC?
This will make a difference as to whether your fan works, which I assume is
a brushless DC fan.
Thanks Laurie & Gary, but I don't have a Multi-meter, and I can't buy one either. No money left and I won't be going into Ballarat for quite a while.
I do have one of those regulated power supplies I bought as a spare laptop power supply. It goes up to 3.5 amps, but it's lowest voltage is 15 volts.
The settings on it are:
15/16/18/19/20/22 volts @ 3.5amps
24v @ 3amps
I think 15 volts will be too much. Especially for the 12v fan.
Quote:
Originally Posted by gary
Do you also happen to know whether the power supply is 13.5V DC or AC?
This will make a difference as to whether your fan works, which I assume is
a brushless DC fan.
The fan works using the 13.5 volt Apple power supply. It is a 12v 1.5W 50mm DC brushless computer fan.
Last edited by ballaratdragons; 01-09-2007 at 08:50 PM.
You won't need the multimeter and I took into account you probably don't
have one. You had mentioned that you had bought the nichrome wire from
Jaycar and earlier in the day I had checked online and saw they only sold one
type which has a resistance of 13.77 ohms per meter, so we just need to know
the two lengths.
Just stick with your 1A power supply for now, but we need to calculate
the total current draw first, hence the need to measure the lengths.
Can anyone work out the current draw for me please? I'm waiting to know whether to construct my set-up, or not.
Any help greatly appreciated
2 Nichrome heaters x 1150mm each (resistance of 13.77 ohms per meter), and 1 x 12v 1.5W 50mm DC brushless computer fan.
All running from an Apple 13.5v, 1.0 amp, 15 VA power Adaptor.
Hi Ken. I'll give it a go, but I'm operating under the disadvantage of not having read the thread - been busy and out under clear skies Sat night - woopee!
1.15m at 13.77 ohms per metre = 15.8 ohm. Connect 13.5 volts to that resistance and the current flow will be 0.85A. Two of these in parallel will draw 1.7A. Add the fan at about 0.2 amp and you reach 1.9A. Nope, I don't think your supply will be capable. Try one length only on the supply - no fan as well, and see what temperature above ambient you reach? Just to try and get a feel for the performance. If you can use twice the length of wire for each heater then maybe you can run them both plus the fan - your supply will be at its limit and will probably drop a bit in voltage output - unless very well regulated.
Hi Ken. I'll give it a go, but I'm operating under the disadvantage of not having read the thread - been busy and out under clear skies Sat night - woopee!
1.15m at 13.77 ohms per metre = 15.8 ohm. Connect 13.5 volts to that resistance and the current flow will be 0.85A. Two of these in parallel will draw 1.7A. Add the fan at about 0.2 amp and you reach 1.9A. Nope, I don't think your supply will be capable. Try one length only on the supply - no fan as well, and see what temperature above ambient you reach? Just to try and get a feel for the performance. If you can use twice the length of wire for each heater then maybe you can run them both plus the fan - your supply will be at its limit and will probably drop a bit in voltage output - unless very well regulated.
Thanks Eric.
But if I use twice the length of Nichrome, it won't even get slightly warmish. Heat is almost undetectable at 1300mm.
Looks like I'll have to use the 3.5 amp power supply, but then I have the other problem. It's lowest voltage is 15v.
L.
Danger, Will Robinson!
