Mike,
I forgot to add that if paralelling them, you will need a resistor who's
voltage rating is higher than the open circuit voltage.
Best,
Will
*********** BEGIN FORWARDED MESSAGE ***********
On 4/24/05 at 11:57 AM Will Matney <craxd1@ezwv.com> wrote:
>Mike,
>
>The resistors model number shows a 225-watt core, 4595 volts. Joe showed
>that the watt rating was too small as the voltage and current you have
>will multiply to more than 225, or 314 watts. You'll notcie too that the
>voltage has been exceeded on this resistor as you should have 5600 Vdc
>open plate voltage at 56 mA, and maybe average 4950 Vdc under load. Both
>together would really heat that up if not blow it. What you might look at
>doing is use two 50K resistors of this size in series so as to divide the
>voltage and current up across two. You would effectively double the rating
>this way and have the same value in ohms for the discharge time of 4
>seconds.
>
>Saftey here is important as NEVER bet on those resistors to discharge
>those caps. I made a dischargeer here that has a big power resistor in it
>(actually 5, 100 watts in paralell). Plus, a switch will cause a relay to
>short out the bank. On the B+ side is a voltmeter with it's own ground to
>show if the bank is discharged. What I do is first place the probe on the
>B+ line and wait a couple of seconds. Then, I hit the pushbutton which
>shorts the rest to ground. Sometimes, you have to do this 2-3 times to get
>rid of any residual charge. You could just short them too but I swear I
>hate that big bang everytime on top of being hard on the components. The
>thing I made gets you buy with this and those caps are safely discharged
>before service.
>
>In you case, I'd get two 50k-225 watt resistors and series them, or two
>200K and paralell them.
>
>Best,
>
>Will
>
>
>*********** REPLY SEPARATOR ***********
>
>On 4/24/05 at 7:28 AM aborg wrote:
>
>>Joe,
>>
>> The bleeder is a Ohmite L225J100K.
>>Thanks too all who have replied, keep the info comming
>>I love the info.
>>73's
>>****************************************************
>>--- "Joe Subich, K4IK" <k4ik@subich.com> wrote:
>>>
>>> Mike,
>>>
>>> Your bleeder resistor is too small.
>>>
>>> 4000 volt transformer with fullwave bridge should
>>> produce at least 5600 volts no load.
>>>
>>> 5600 volts across 100K -> 56 ma
>>>
>>> 56 ma * 56 ma * 100K = 313.6 watts
>>> 313.6 watts >> 225 watts
>>>
>>> At a minimum, you need either: (1) a pair of those
>>> resistors
>>> in series, (2) a 200 K 225 watt bleeder or (3) a
>>> 100K 500 watt
>>> bleeder. Even then, you will be not have a lot of
>>> safety
>>> factor and probably need to provide cooling for the
>>> bleeder.
>>> Safer yet would be a (series) string of four 50 K
>>> 225 watt
>>> bleeders.
>>>
>>> Finally, is the resistor rated for > 5 KV? Most are
>>> not.
>>>
>>> 73,
>>>
>>> ... Joe, K4IK
>>>
>>>
>>>
>>>
>>> > -----Original Message-----
>>> > From: amps-bounces@contesting.com
>>> > [mailto:amps-bounces@contesting.com] On Behalf Of
>>> aborg
>>> > Sent: Sunday, April 24, 2005 9:44 AM
>>> > To: Amps Amps
>>> > Subject: [Amps] Bleeder Resistor Inquiry
>>> >
>>> >
>>> > I am currenty building a HV Power Supply using a
>>> > 4800vac pole pig, 40uF 5kv oil filled cap , 10kv
>>> PIV
>>> > rectifier board, 20 amp variac and a 100k 225watt
>>> > bleeder.
>>> >
>>> > The initial power up started well without the
>>> bleeder
>>> > connected to the circuit after 30 min burn-in no
>>> > problems. Discharged the circuit and added the
>>> 100k
>>> > bleeder and 5 mins the bleeder starts to smell and
>>> the
>>> > exterior paint starts to bubble. Shut it down and
>>> > examined the circuit, all seem accurate.
>>> >
>>> > Question : Is my bleeder to small ?
>>> >
>>> > P.S. : The variac was set at 4KV at all times.
>>> >
>>> > Mike-KK4MS
>>> > a_borg@yahoo.com
>>> >
>>>
>>>
>>
>>Mike-KK4MS
>>a_borg@yahoo.com
>>
>>__________________________________________________
>>Do You Yahoo!?
>>Tired of spam? Yahoo! Mail has the best spam protection around
>>http://mail.yahoo.com
>>_______________________________________________
>>Amps mailing list
>>Amps@contesting.com
>>http://lists.contesting.com/mailman/listinfo/amps
>
>
>
>_______________________________________________
>Amps mailing list
>Amps@contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
>
*********** END FORWARDED MESSAGE ***********
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|