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12vdc heater supply in Poddwatt
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Author:  Rog63 [ 18 Apr 2020, 06:45 ]
Post subject:  12vdc heater supply in Poddwatt

Hi,

I'm struggling to understand what is happening with this part of the power supply (diagrams attached).

With nothing connected to the circuit I measure 15v at the dc supply output terminals which is too high for the heaters. So I put in a voltage divider (2 ohm adn 8 ohm 5W resistors). When I measure the voltage at the junction of the two resistors I get 10V. Calculating that back would give me 12V across the whole divider and I measured it at 12.6 vdc.

I calculated the total resistance from the heater circuit and it comes out at around 11 ohms. My question is, if I put the tubes in does it have the same effect as the voltage divider circuit? If so I can remove the voltage divider, plug in the tubes and feel safe that nothing bad is going to happen (to the heaters at least!!). I think this is probably correct but wanted to check first... OR....

Do I leave the voltage divider in place and make my 12vdc connections to the original terminals which are now measuring 12.6 vdc. ?

Thanks

Rog

Author:  Suncalc [ 18 Apr 2020, 08:59 ]
Post subject:  Re: 12vdc heater supply in Poddwatt

Ditch the voltage divider and wire it like Bruce indicated. With the load it should be fine. If you do find the voltage too high (e.g. >13.8v) then add a single series resistor to drop some voltage.

Author:  Rog63 [ 18 Apr 2020, 11:17 ]
Post subject:  Re: 12vdc heater supply in Poddwatt

Thanks Matt,

I did that and heater wise everything is fine. got another problem though but I'll search the forum before posting about it.

Rog

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