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Old 7th November 2012, 07:14 PM   #11
dazed2 is offline dazed2  Canada
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AndrewT
When you mean power thermistors, do you mean CL30 or CL60's? Shouldn't I be able to parallel 3 or 4 of them?

So from what you said then perhaps the best way would be to have two relays and have the second one make before break when switching out the thermistors to eliminate current spike.
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Old 8th November 2012, 08:06 AM   #12
AndrewT is offline AndrewT  Scotland
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DO NOT parallel Power Thermistors !
Series connect, if you need moire resistance with the current rating you have selected.
Yes, CL are Power Thermistors. Does the datasheet show a typical slow charge circuit?
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Old 10th November 2012, 05:29 AM   #13
bobfig is offline bobfig  United States
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Quote:
Originally Posted by bobfig View Post
hello i have a question about what switch i can use. i found one i like but im not sure on how much current the switch will need to handle to turn on and off the amp.

switch in question
MP0045/1E2BL012 Bulgin | Mouser
im waiting for a answer still. im wondering if this switch would handle a 600va transformer with 40,000uf capacitor bank. source is 120v.

Last edited by bobfig; 10th November 2012 at 05:38 AM.
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Old 10th November 2012, 06:44 AM   #14
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3 A switch is too weak. You should look for a 10 A switch at least.
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Old 10th November 2012, 11:03 AM   #15
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by bobfig View Post
................. 600va transformer............... source is 120v.
thats a close rated fuse of ~5A

Why would you even think of using a 3A switch?
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Old 10th November 2012, 02:54 PM   #16
bobfig is offline bobfig  United States
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well i like the style of the switch but ok. i wasnt sure if all the power was going threw the switch or just the power that was needed for the relay to switch it on. also was thinking since it was 250v rated 3a it would be 120v rated 6a.
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Old 11th November 2012, 01:13 PM   #17
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Quote:
Originally Posted by AndrewT View Post
I think there should be some "design" notes added for the current limiting resistor values.
The 4 resistors R15 to 18 are specified @ 180r.
Is this for 110/120Vac and/or 220/240Vac?
Is this for 200VA to 1000VA transformers and/or any size transformer?

I know from experience that 45r (180/4) works on 220/240Vac for medium sized transformers in the range 200VA to 500VA.

But smaller transformers would need higher value resistors and larger transformers would need lower value resistors.
I expect that 110/120Vac transformers will generally require lower value resistors to effect similar current limiting.

A simple table showing VA & Vac combinations with appropriate resistor values would be very useful to less experienced builders.
Sorry for arriving late on this thread, so much to update in so little time really.

In the build guide there is some basic notes on the choice of resistors R15 to 18.

The actual prototype was used in an 800va transformer, with R15-18 180R each.

Thanks for the feedback and suggestion.
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Old 11th November 2012, 01:16 PM   #18
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Quote:
Originally Posted by AndrewT View Post
here's a suggestion for discussion

. . . . . . . . . .Vac
VA . . . 115Vac . . 230Vac
100 . . . . 270r . . . 390r
200 . . . . 180r . . . 270r
400 . . . . 120r . . . 180r
800 . . . . .82r . . . 150r
1600 . . . . 68r . . . 120r

The resistor values shown are from the E12 range. If these are difficult to find in 5W wire wound, use the nearest E6 value.

For 230Vac the values shown allow a T rated fuse that is close rated to be used for reliable start up over the long term.
eg. 500VA fused with T2A will start with 40r to 50r in the primary circuit (equivalent to 160r to 200r for the four 5W resistors)

Are these values you mentioned worked from actual experience? This collection of information can probably be included in a small section in the build guide for less experienced builders.
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Old 16th November 2012, 06:49 AM   #19
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Was the soft start designed to take the place of the CL60 type thermistors as shown in the PASS psu schematics ?
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Old 16th November 2012, 09:41 AM   #20
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Quote:
Originally Posted by thor61 View Post
Was the soft start designed to take the place of the CL60 type thermistors as shown in the PASS psu schematics ?

not intentionally, I was thinking of other amplifiers during that time.

but sure it can replace the CL60 thermistors and provide soft start to those amplifiers too.
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