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 Post subject: 12vdc heater supply in PoddwattPosted: 18 Apr 2020, 06:45

Joined: 11 Sep 2019, 10:56
Posts: 25
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

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 Post subject: Re: 12vdc heater supply in PoddwattPosted: 18 Apr 2020, 08:59
 Project Author

Joined: 06 Apr 2009, 10:08
Posts: 1748
Location: US Pacific Northwest
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.

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Matt
It's all about the Glass!

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 Post subject: Re: 12vdc heater supply in PoddwattPosted: 18 Apr 2020, 11:17

Joined: 11 Sep 2019, 10:56
Posts: 25
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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