Dew Heater Power

[scitmon]

Hello, I'm looking into buying some dew heaters for my setup and I'm wondering if I'm going to need an additional power supply.  I'm currently using https://www.firstlightoptics.com/power-accessories/nevada-ps-08-6a-8a-regulated-linear-power-supply.html which is rated 6-8 amps, to power my SW AZ-EQ6-GT mount.  I've read that the max potential power draw is 4 amps, and I'm looking to add https://www.firstlightoptics.com/dew-prevention/hitecastro-four-channel-four-port-dew-controller.html along with up to 3 dew heater strips for my scope, guidescope and reducer/flatenner. 

Am I likely to need another power supply?

If not, would powering the mount via the dew controller with https://www.firstlightoptics.com/astronomy-cables-leads-accessories/lynx-astro-silicone-21mm-dc-jack-to-female-cigarette-socket.html work well?

 

 

[Moonshane]

Interested in this too as I think dew control would be beneficial especially on my finders.

[knobby]

You'd need to work out the current draw on your straps, my 8"sct strap draws about an amp on full power and the 3" frac strap is about 0.7 amps.

You will probably be near the max of the power supply you have at times but the mount surely won't pull 4 amps very often, it's probably around 1 amp when just tracking ?

Edit, just found this .

 

[RayD]

Don't forget the current figures quoted are at 12V, at 13.8 these will reduce.  I would say you are fine as the maximums are just that.

There is a handy table here to work out your strap current, which as noted by @knobby will likely be very low.

[scitmon]

Thank you for the replies, yes I think I will be OK.  I contacted FLO about the strap lengths and asked about the power too.  They said should be more than enough, my mount would pull around 3 amps when slewing at full speed and I've observed it being less than an amp when tracking.  The straps would be around 1.2 amps each on full power, which they won't be I presume.   Sounds like I will be fine.

[Lonestar70]

2 hours ago, RayD said:

Don't forget the current figures quoted are at 12V, at 13.8 these will reduce.  I would say you are fine as the maximums are just that.

@knobby

Sorry RayD but that is not strictly true.

If the resistance of the strap stays the same (which it would) then the current will increase with an increase in applied voltage.

The current would only fall for the same output wattage, however, this will not be the case for a dew strap since it's resistance is fixed.

1 Watt @12v = 0.083A = 144.5 ohms resistance. (12v/0.083A)

13.8v applied to 144.5 ohms = 0.095A

hence 13.8v x 0.095A = 1.311 Watts.

To obtain the same 1 watt at 13.8volts would require the resistance of the strap to increase (by magic) to 190.34 ohms which, of course, it cannot do.

You could, of course, add a small series resistor of say 47 ohms (or a variable resistor) to either lower the fixed output power or be able to adjust it during use using the variable resistor. (something around the 100-150ohms would be about right and with a 1 Watt rating).

I hope that all makes sense.

Non of the above would suggest that the OP's power supply would be incapable of running both the mount and the dew straps at the same time... as has been stated... the mount will only have a higher current draw (3-4 amps) when slewing otherwise it would be around the 1 amp level... so a 6 - 8Amp supply will be more than adequate.

Keep happy and clear skies.

 

[RayD]

1 hour ago, Lonestar70 said:

Sorry RayD but that is not strictly true.

If the resistance of the strap stays the same (which it would) then the current will increase with an increase in applied voltage.

The current would only fall for the same output wattage, however, this will not be the case for a dew strap since it's resistance is fixed.

1 Watt @12v = 0.083A = 144.5 ohms resistance. (12v/0.083A)

13.8v applied to 144.5 ohms = 0.095A

hence 13.8v x 0.095A = 1.311 Watts.

To obtain the same 1 watt at 13.8volts would require the resistance of the strap to increase (by magic) to 190.34 ohms which, of course, it cannot do.

You could, of course, add a small series resistor of say 47 ohms (or a variable resistor) to either lower the fixed output power or be able to adjust it during use using the variable resistor. (something around the 100-150ohms would be about right and with a 1 Watt rating).

I hope that all makes sense.

Non of the above would suggest that the OP's power supply would be incapable of running both the mount and the dew straps at the same time... as has been stated... the mount will only have a higher current draw (3-4 amps) when slewing otherwise it would be around the 1 amp level... so a 6 - 8Amp supply will be more than adequate.

Keep happy and clear skies.

 

I think it is pretty clear I was actually referring to the mount, noted as 4A max, not the heaters which we know nothing about.

Give it a go.  I have this mount and I have.

[Geoff Lister]

If you think you might be close to the current limits, you could always switch off the heaters just whilst slewing, and on again when tracking.

[Waldemar]

Yes, like Geoff said, you will be on the edge if everything is running and slewing. The power rating of your supply is maximum, not nominal.
I would go for a heavier one, or a separate one for the dew heaters, which is a better option anyway.

Try not to use the cigar lighter plugs, They just s...!!! Use real power plugs. Even the banana plugs are far better then the lighter plugs.
The contact area of the central plus of a cigarlighter is very small and springloaded. A recipe for disaster.
I have no idea why those things are used so much for astro equipment... get connectors which are constructed for a solid connection, these things are just meant to be used for a few seconds to lite your cigar.

[Geoff Lister]

The only good thing that these connectors have going for them is that the plug is large enough to have space for an internal cartridge fuse.

If the car manufacturers are going to provide a viable alternative, they are going to have to overcome significant market inertia. Then there is the problem in selecting an alternative; USB - A is fine for 5V @ 500mA, but there is not a (relatively) idiot-proof industry standard connector for 12V at up to 10A continuously, that will not melt its way through a plastic dashboard under fault conditions.

[Waldemar]

1 hour ago, Geoff Lister said:

The only good thing that these connectors have going for them is that the plug is large enough to have space for an internal cartridge fuse.

If the car manufacturers are going to provide a viable alternative, they are going to have to overcome significant market inertia. Then there is the problem in selecting an alternative; USB - A is fine for 5V @ 500mA, but there is not a (relatively) idiot-proof industry standard connector for 12V at up to 10A continuously, that will not melt its way through a plastic dashboard under fault conditions.

Well... that is what I mean: they are meant for cars, NOT for astro gear

[Geoff Lister]

6 minutes ago, Waldemar said:

Well... that is what I mean: they are meant for cars, NOT for astro gear

I fully agree, but over the last few years, since smoking in a confined space (including in cars) became illegal, or classed as anti-social, the car manufacturers have fitted every car with a socket, labelled "12V", with the same main dimensions, and electrical interface, as the 'old' cigar lighter holder. Until there is international agreement on a replacement, we are, sadly, stuck with this connector, on any equipment that has optional use on vehicle power.

Given the track record of mobile phone manufacturers' multiple choices of power/data connectors, I am not expecting an astronomy-friendly connector any time soon, so will stick with the 5.5mm OD/2.1mm ID/14mm long power jacks that fit all my powered mounts, and a strain-relief clip, close-by on the cable, to stop the plug being pulled out too easily by cord-wrap.

Geoff