Is there a plug to connect a specific heater strap 3.5mm plug to a Kendrick type unit

[g__day (Matthew)]

Hi all,


I purchased and Kendricks dew heater unit and two straps for my OTAs yesterday and installed these.

Bintel said put the heater straps on the OTA exactly where the front lens will be within my lens cap - so I did and left them on last night at about 30% power. I plugged the Kendricks unit in to an old 12V 4amp transformer and it seemed to work well.


I think the Kendrick unit has a very flimsy looking on off switch - hmmm...

But the point of my post - I have a heating strap I would like to put on my 88mm guide scope. i just have to figure a way to connect its i guess 3.5mm transformer plug to the RCA type it appears Kendricks use?

Does Jaycar or anyone sell such a converter and what are they called?

Is this safe to do?

Thanks, Matt

[AstroViking (Steve)]

Such a convertor would be an RCA-male (for plugging into the Kenricks) converting to a female DC power connector (for plugging the dew strap into).

The DC power connectors are measured by the diameter of the inner pole. Most common is 2.1mm (most audio stuff) or 2.5mm. The barrel length is usually 10 or 14mm. Be sure to get the one you need - close enough isn't good enough.

It's easy enough to wire up a suitable adaptor. The plugs / sockets go for a couple of dollars each.

Cheers,
V

[Startrek (Martin)]

Kendrick Dew control gear is mostly all RCA connectors
Jaycar and many other suppliers carry all types of proprietary RCA leads or you can buy cable plus parts and solder up your own
I made my own with fig 8 0.75mm2 2 core V75 speaker wire and RCA male and female plugs ( all purchased from Jaycar )
Cheers
Martin

[Dave882 (David)]

Not sure for 3.5mm, but this was my solution to connect to standard 12v 2.1mm plug:
https://www.astrodog.com.au/product/...r-patch-cable/

[g__day (Matthew)]

Steve - noted - would bring the heater cable and its end plug to a jaycar store to check ther solution mates well - aways!


Martin - reckon that is how I will go - will likely be a cable purpose built!

David - would be a perfect solution if it were about 1 metre long and ending in a female socket - the cable heater I have has a male end. But I could mate that to a 1 metre female to female cable and it would all work!

[PhilTas (Phil)]

Hi Matt,

A couple of questions first -
1. do you have a soldering iron and tools to fit a new connector? And the skills to do so?
2. Are you ok with cutting the DC plug off the heater lead (the one with the power connector) ?
3. Or do you want to keep the DC connector, and have an adaptor to make the RCA connection to the Kendrick?

If 1 and 2 are both yes, then buy an RCA plug PP0242 from Jaycar, cut the DC Power connector from the heater lead, and solder the RCA on.

If 1 is no, and 2 is yes, then buy the RCA Plug with Screw Terminals PA3717, cut the power connector off, strip off the insulation from the 2 wires (about 5mm should be enough), and connect one wire to each terminal on the PA3717.
Polarity should not be an issue, but send a photo of the complete heater band just to be safe. Most heaters are just made from resistance wire, so the centre of the RCA socket on the Kendrick could connect to either wire on the heater. If the band is flat for all of it's length, then it should be fairly safe to just connect the wires without worrying about positive and negative polarity.
But if there is a module or small box on the band then it is probable that there is some circuitry inside - polarity is then important, you will have to make sure that positive goes to positive etc.
If you have access to a multimeter, measure and note the resistance reading between the centre contact and the outer barrel of the DC connector. Then reverse the multimeter leads and repeat the measurement. If both measurements are the same, it's unlikely that the heater band contains any electronics. If the two readings are markedly different, then polarity becomes important, and you must connect the centre wire from the cut off plug to the positive terminal of the PA3717.

If 1 is no and 3 is yes, then Jaycar also sells a DC Socket Connector with Screw Terminals PA3713.
EITHER Buy a short length of 2-core cable, connect the PA3713 to one end, and the PA3717 to the other end. Note the comments about polarity are still important. OR
Astrodog sells an adaptor lead - DC Connector on one end with RCA on the other. If you go this way, buy DC Power Adaptor PA3701 from Jaycar which will join the two male DC Plugs.

See attached screenshots.

If you want to discuss or need more info, send me a PM.

Cheers Phil

[g__day (Matthew)]

Hi Phil,


Huge thanks for such a detailed answer = wow! I have wired and soldiered micro boards from scratch - so yes pretty handy with a soldiering iron and multimeter / oscillscope in my day!

Off to Jaycar we will go this week. Meanwhile ordered another Kendrick unit so if all goes wrong I am covered and if I can build it I have a clean spare!

Greatly appreciated,
Matthew

[PhilTas (Phil)]

No Worries Matt,

When you reply to a query you never know what the skill level/experience is of the OP. So at the risk of telling you how to suck eggs I figured it is easier to be detailed. Sorry if I underestimated you. Do you have a defence background?

I'd be interested in your opinion on the Kendrick dew heaters and controllers.
I have very little need for such in Darwin, and can mostly manage with hoods to keep the dew at bay.
But having a controller and heaters might be handy at some time.

Cheers Phil

[g__day (Matthew)]

No maths and computer science honours before moving into consulting - but I loved the hardware side of IT as much as the software development!

Your explanations were top notch!