dew heating systems - what is the most power efficent and the best to use
I am after some help with respect to dew control heating straps and dew controllers?
I am thinking of using a 80 or 100 AH deep cycle battery to power it, but what is the most power efficient system, Kendrick, thousand oaks, dew buster? Which straps are the best to use?
And lastly, what is value for money?
Looking at running a dew strap for the finder scope, 127 scope, 2x 80mm scope
I bought the lowest model Kendrick model VI which has 4 ports and I also got a Kendrick 3" heater strap for my 100mm Genesis. It's the best accesssory I've ever bought, period! Works like a dream, but it does sap the power a bit. I hooked an amp meter in line once, and with the controller box set at about medium, which I think means heating 'on' approx 30-40% of the time, current jumps from a basal of 0.2 amps up to 0.5-1.0 amps when it cycles the heater strap. So 4 heaters at once will really sap the power. The higher model Kendrick controllers are all digital and more sophisticated, a lot more $$ and probably suit your needs better - but complete over kill for what I need.
Sorry, I have no comparo data nor experience with any other brand, but my Kendrick basic model does a brilliant job for me. I have no idea why I went without one for so long. Fox.
David, I have a Thousand Oaks controller and various Dewnot straps and a DG-1 heater on the secondary. I also have a 12V gel battery with an ammeter in the circuit so I can monitor consumption. When I get time, I'll plug in various heaters, twiddle the dials and report the current consumption.
The other very dewy night, I wanted to point my camera at the sky. I took my finderscope dewnot heater and wrapped it around the lens. I found a little AC powerpack lying around which was spec'd at something like 10V 200mA and connected it and let it rip. A rough measurement suggested it was drawing 300mA! Well it ran for several hours, powerpack didn't blow up or even feel hot, heater strap didn't feel to be overheating and camera lens stayed completely clear in the misty air while dew settled everywhere else!
The most power efficient system is any one that has a temperature feedback loop. These units only provide enough heat to keep the optics a set delta above ambient, hence always run at the lowest level required to maintain said delta
I run a home made one, but irrespective of model, i found it was beneficial to have a wide insulating strip outside of the heater. The sensor sits under the insulation, but away from the heater strip, hence getting a true feedback, with lots of built in damping.
Hi Dave, well I just did a little re-test to rejog my memory.
My Kendrick model VI (most basic unit) cycles 40% 'on' when set to 'Min', up to 100% 'on' when set at 'High', so I guess when I run at 'Medium' it is around 60% 'on' cycle. When I run my LXD75 at idle, there is barely any amp draw (maybe 0.1 to 0.2 amp), but with fast dual-axis slewing the amp draw is 0.5. When the dew strap cycles 'on', the total amp draw is 1.5 amps, so my meagre 3 inch dew strap pulls a full amp when its heating.
Assuming that 4 separate similar size dew straps (for your application) will each draw 1 amp, would I be correct to say that is approx. 4 amps alone (for ~60% of the time) for anti-dew, using the basic Kendrick unit. Hey, your 80-100AH source is not at all ridiculous when you look at the numbers!
I guess the higher model controllers with temp feedback etc., individual channel control etc. is where the power-management efficiency comes into play. You get what you pay for, but the most basic Kendrick unit with 4 straps is one possible option. The controller and strap, new, cost me $260 from Bintel and it's well worth it my book. Fox
I have the Kendrick Digifire 7 on the 18" Obsession with the Dewnot Heater straps. The Thousand Oaks controller is a better unit than the Kendrick IMO and I will be getting the Thousand Oaks on my next scope. There are two main reasons. One being the dials are easier to use on the Thousand Oaks than the finger pressure switches on the Kendrick Units. And most importantly, while both units have low voltage cut out circuits, you can bypass it on the Thousand Oaks, but cannot bypass it on the Kendrick. Consequently, whenever your voltage drops down a bit the Kendrick unit shuts down, notwithstanding there is still plenty of power there to run the heater straps.
The Dewnot straps are excellent. Peter read at SDM sells it all. It's not cheap but IMO its the best.
Word is, that Dewbuster are one of if not 'the' best dew controllers. I ordered a Dewbuster and a load of DewNot strips which are supposed to be the best combination, ie. the best most efficient heater strips and the best and most efficient Controller. Sure that lot was about 300 euros all told but quality costs.
Haven't actually fitted them yet but if the level of customer service I received from both Ron Keating at Dewbuster and John Marstiller at DewNot is anything to go by, then I have no doubt they'll meet my expectations. I must have sent 30 emails between those two guys asking questions and nailing down the custom specs I wanted and they both answered all of them promptly with long comprehensive replies. Customer service second to none.
The DewBuster will become the lynch pin and centrepiece of my dob project. It is highly customisable. The spec I settled on was as follows:
1x Temp Sensor Controlled output for a secondary heater
7x Regular heater outputs. These run at 40% power
1x 3v Regulated Output to power a GLP
4x 12v Outputs to Power 12v gear
As you can see it can be configured with up to 15 outputs of any combination.
I'll be running a secondary heater, a 2" heater for EP, a 3" heater for Stellarvie F80 finder objective, a 2" Heater for F80 EP, a .925" heater for under the GLP, a 3v ouput to Power my GLP, a handset heater for my Intelliscope handset and finally a further 2x 2" heaters that will heat a scope mounted EP box I am making. (ie EP's will sit on a metal rack inside a small insulated box. These heater strips will be affixed to the rack and the heat will conduct through the rack into the metal barrels of the EP's). In addition I am powering my 5 fans via a fancontroller, A large LED scanner(don't ask!! ), a JMI TNT motor drive and another miscellaneous item
In effect the Dewbuster is my Dew Controller, Power distribution rail and low battery level indicator/cutout/saver. ie it flashes a low battery warning and eventually cuts off if the battery drops to 11v IIRC before the battery is damaged.
AFAIK the amperage of the Dewnot strips is quoted @100% power, so once I toted everthing up including the 12v gear I was coming up with about 5 amps. Thus a 26AH batter should give me at least 5 hours which is enough for a session. The fact that I will infact be running most of the strips at 40% power and not all the 12v gear at once means, I would in reality probably have enough power for a dusk till dawn alnighter even with all these strips and gear and a 'lowly' 26AH.
As for the Dewnot stips. John Marstiller can customise these too for a small fee. I wanted to provide a cheap, functional dew control system with my Orion 12" Intelliscope I am selling. John was able to custom adapt one of his Binoviewer Strips to use 2" strips instead if 1.25", and lengthen the cord between the bino strips. These strips also have a power take off lead for plugging in another strip. The way I will be using it, or should I say the new owner of the scope is thus: One bino strip for the single EP, The other Bino strip around the Orion 9x50 Raci objective and a .925 strip plugged into the power take off. Just one lead goes down the scope and is plugged into one of the new Kendrick Microlite controllers.
I have the Kendrick Digifire 7 on the 18" Obsession with the Dewnot Heater straps. The Thousand Oaks controller is a better unit than the Kendrick IMO and I will be getting the Thousand Oaks on my next scope. There are two main reasons. One being the dials are easier to use on the Thousand Oaks than the finger pressure switches on the Kendrick Units. And most importantly, while both units have low voltage cut out circuits, you can bypass it on the Thousand Oaks, but cannot bypass it on the Kendrick. Consequently, whenever your voltage drops down a bit the Kendrick unit shuts down, notwithstanding there is still plenty of power there to run the heater straps.
The Dewnot straps are excellent. Peter read at SDM sells it all. It's not cheap but IMO its the best.
Word is, that Dewbuster are one of if not 'the' best dew controllers. I ordered a Dewbuster and a load of DewNot strips which are supposed to be the best combination, ie. the best most efficient heater strips and the best and most efficient Controller. Sure that lot was about 300 euros all told but quality costs.
Haven't actually fitted them yet but if the level of customer service I received from both Ron Keating at Dewbuster and John Marstiller at DewNot is anything to go by, then I have no doubt they'll meet my expectations. I must have sent 30 emails between those two guys asking questions and nailing down the custom specs I wanted and they both answered all of them promptly with long comprehensive replies. Customer service second to none.
The DewBuster will become the lynch pin and centrepiece of my dob project. It is highly customisable. The spec I settled on was as follows:
1x Temp Sensor Controlled output for a secondary heater
7x Regular heater outputs. These run at 40% power
1x 3v Regulated Output to power a GLP
4x 12v Outputs to Power 12v gear
As you can see it can be configured with up to 15 outputs of any combination.
I'll be running a secondary heater, a 2" heater for EP, a 3" heater for Stellarvie F80 finder objective, a 2" Heater for F80 EP, a .925" heater for under the GLP, a 3v ouput to Power my GLP, a handset heater for my Intelliscope handset and finally a further 2x 2" heaters that will heat a scope mounted EP box I am making. (ie EP's will sit on a metal rack inside a small insulated box. These heater strips will be affixed to the rack and the heat will conduct through the rack into the metal barrels of the EP's). In addition I am powering my 5 fans via a fancontroller, A large LED scanner(don't ask!! ), a JMI TNT motor drive and another miscellaneous item
In effect the Dewbuster is my Dew Controller, Power distribution rail and low battery level indicator/cutout/saver. ie it flashes a low battery warning and eventually cuts off if the battery drops to 11v IIRC before the battery is damaged.
AFAIK the amperage of the Dewnot strips is quoted @100% power, so once I toted everthing up I was coming up with about 5 amps. Thus a 26AH batter should give me at least 5 hours which is enough for a session. The fact that I will infact be running most of the strips at 40% power means I would in reality probably have enough power for a dusk till dawn alnighter even with all these strips and gear and a 'lowly' 26AH.
thanks Keith, RB is trying to put me onto the Dewsbuster as well
While I haven't had the chance to try out various types of dew control.
I did install a Thousand Oaks controller and Dewnot straps and Telrad
heater on my 16". It's been a lovely investment after years of fighting
dew with a hair dryer. Just need to upgrade the 2" Dewnot EP strap
as it only goes about 2/3's the way around my 31mm t5 lol. But it is
nice to walk away from the EP and come back to find it clear to use.
So I'll also vouch for the Thousand Oaks/Dewnot setup.
After deciding I needed dew heating, I read all the reviews I could.
Last year, I purchased the Thousand Oaks controller and Dewnot heater straps and the Astrosystems DG1 secondary mirror heater - all from SDM Telescopes and for a lot less than the current list prices (had a win on the exchange rate!)
I got one heater strap from a US supplier - threw it into an order to get the best shipping deal.
I know you don't want the DG1, but for information, it is an intelligent heater with a sensor on the mirror and one in the ambient air. It maintains the mirror a set amount warmer than the ambient. Just feed it with 12V. The Thousand Oaks controller has a straight through (uncontrolled) 12 V out. Some people power their Argo Navis from here. I power the DG1.
I measured the resistances of the Dewnot heaters tonight and the current they drew from the battery, through the controller. I have a 10A panel meter in the battery line so I cannot read any better than 0.1A. I wasn't going to wire a multimeter into the line tonight, sorry.
To finish the DG1 story, it drew a steady 0.2A current, whether heating or not (according to the indicating LED)
Now, the resistances of the Dewnot heater straps:-
DNO11 (10" - to heat my eyepiece box) 9.7 Ohms
DNO09 (8" - to heat my C8 corrector plate) 13.2 Ohms
DNO04 (3" - to heat my finderscope objective or a DSLR camera lens) 24.5 Ohms
DNO03 (2" - to heat a 2" eyepiece) 38.0 Ohms
DNO02 (1.25" - to heat a 1.25" eyepiece) 48.7 Ohms
I connected the controller to the battery. The current draw of controller was not detectable on the 10A panel meter.
The controller works by delivering a proportion of the duty cycle from 0% at "OFF" to 100% at "HI". At the "MED" point, it seems to be delivering 50-60% of the cycle. That is, it cycles the output on and off, turning the heater current on fully for more and more of the cycle as the knob setting is increased. At HI, the output stays on 10% of the time.
At the HI setting, the battery drain was:-
DNO11 1.3A
DNO09 1.1A
DNO04 0.5A
DNO03 0.3A
DNO02 0.2, maybe more like 0.25A
Hey, Ohms law generally works - not sure about the 8" strap!
I turned the DNO11, DNO09, DNO04 and DNO03 all to HI and the meter read 2.9A. Seems a bit lower than the sum above, but we are in the right ballpark.
I fit the DNO11, DNO04, DNO03 and DNO02 to my 12" dob. At that stage, the controller is fully utilised. Now, even on the dripping nights, I've never needed to be higher than MED on the controller, so I'd guess I'd be drawing an average of 50% of 2.4A = 1.2A (plus the steady 0.2A to the DG1 makes it 1.4A). I've never pulled much charge out of a moderate size gel battery over 4-5 hours. (plug the 12V, 90W hairdryer into the parallel socket and that's a different story. But it has stayed packed away since I installed this dewheating.)
I second John's comment of the desirability that the Thousand Oaks controller can have the low voltage cutout disabled. This is designed to prevent you drawing so much power from your car battery that you have insufficient left to start the engine.
Yes, the dewbuster is more elegant since it senses temperature and delivers only the heating required. The Thousand Oaks, however, does what works for me.
That was a useful exercise for me. I need to check where I can connect a little AC mains powerpack (DC out, but even AC would work) and power a dew heater in a situation where I cannot use the controller. (Some folks at Snake Valley will recall this cable hanging through the air connecting the controller on the Dob to the corrector plate heater on the C8. I ran into it a few times!
To comment on Rob's experience. I would normally cap the eyepiece in the focusser if I'm stepping away. I routinely have the eyepiece in the focusser fitted with a heating strap. It's nice to put your hand in your pocket while having coffee in the kitchen, feel the eyepiece cap which should be on the eyepiece, and think - doesn't matter. Sure enough, mist and dew all around but that glass is crystal clear when you walk back to it 15 minutes later!
This has a description of my simple unit
I have three or four other models depending on complexity reqd.
I still havent got round to it yet, but i reckon it shld be feasible to make a thermostatic controller built into the strap using surface mount components. That way all you need is a 12V supply
Even neater then.
There has to be a good reason why someone who owns a Kendrick Digifire 7 told you he wouldn't have another one. That would be me. There has to be an even better reason why someone who fitted the Kendrick Digifires to every scope he sold (Peter Read at SDM), changed over and now fits the Thousand Oaks system to all his scopes.
I have to ask why you even bothered posting the question because none of the advice you were given sent you in that direction.
You could have had my Kendrick Digifire 7 very very cheap Every time you do a slew and the servo motors on the Servocat Drive kicks in, the low voltage cutout on the Kendrick Digifire 7 also kicks in It's a piece of crapola from my point of view. Probably the same reason Peter Read doesn't use them anymore either.
), a JMI TNT motor drive and another miscellaneous item 
Every time you do a slew and the servo motors on the Servocat Drive kicks in, the low voltage cutout on the Kendrick Digifire 7 also kicks in 
