Power Supply- I am so confused...

mental4astro (Alexander) · #1 03-11-2010, 10:43 AM

Hi all,

I've been wanting to make sure I have a good enough 12V power supply for my dew zapper straps to last all night, both as a portable option and even a mains converted supply. I did a search before starting this thread as I was aware this topic has been raised many times. Yet all this did was confuse me something silly. Electronics is not my stregth, so I need some Plain English help here, please.

Gear: Kendrick Dew Remover Model VI running at medium setting, and upto 6 heating straps, I think something 69.4W, 5.78A total (at a pinch).

Portable: I have been using a "jumpstarter" power source, 12V 17Ahr. Fully charged and used for only about 4hrs, the multimeter showed its residual charge was only 10.5V. This alarmed me. Should I be? Is there any maintance that needs to be carried out on this unit? Am I OK power wise with this unit?

Mains: I've read about problems with the cheaper 12V DC power supplies. In a nut shell, what will give me what I need that won't blow up or burn my pocket?

Many thanks,

Mental.

mswhin63 (Malcolm) · #2 03-11-2010, 10:54 AM

10.5V is too low and can adversely affect the battery getting that low.

Just a question do you want to operate other gear as well?

If so can you add the power rating of all the other stuff?

michaellxv (Michael) · #3 03-11-2010, 10:59 AM

Portable: A load of 5.78A on your 17Ahr battery is going to exhaust it in just under 3 hours. Re-read the threads on deep cycle batteries, but they will cost you more.

Mains: Your average 12V plug pack will only go up to 1A so you will need to spend more on a decent power supply.

erick (Eric) · #4 03-11-2010, 10:59 AM

Yep, mental - 6A for 4 hours would suck a 17AHr battery dry! How long do you want to draw that current for? If say 6-8 hours, you should probably look for a 50-80 AHr battery to give you some reserve by end of the night.

If $s can stretch, then an AGM (Absorbed glass mat) seem to be considered the best.

I bought an 80Ah (I think it was) from these guys, from their ebay shop:- ausjacko http://stores.ebay.com.au/indyindust...eboardproducts

Fair price - going well so far, but I'll give it a solid workout this coming weekend.

mental4astro (Alexander) · #5 03-11-2010, 11:02 AM

Hi Malcom,

At the moment just the dew system. May be one day an Argo Navis & Servo-Cat, but not in the fore seeable future.

Sometimes my laptop at star parties, but that is rare, to run a little webcam. But I'd just get a separte power source for it. Not frequent enough to count it in really.

Eric, yes, 8, 10 hrs.

erick (Eric) · #6 03-11-2010, 11:14 AM

If you have access to 240V mains, then get this power supply from the Dick:-

http://dicksmith.com.au/product/Q175...y-13-8v-dc-23a

I have used one of these for a few years and it can drive quite a lot of gear.

1) keep it out of the rain and heavy dew (just cover it with plastic)

2) disable the green light in the switch and even replace the green LED with a red LED - they light up the observing field!!

mswhin63 (Malcolm) · #7 03-11-2010, 11:16 AM

Battery minimum 80AH

Mains minimum 8A PSU - about the closest I could find in a short time - http://www.jaycar.com.au/productView...T&SUBCATID=647 - enough power at a reasonable cost. Could do one better but at least you now know what to look for.

I hope to have my web sight up soon and supply some of these parts just opening a bank account today,

[1ponders] (Paul) · #8 03-11-2010, 11:39 AM

I use the same one Malcolm linked to and also have the 10a version. Never missed a beat.

mental4astro (Alexander) · #9 03-11-2010, 11:43 AM

Thanks for the leads, gentlemen.

mithrandir (Andrew) · #10 03-11-2010, 06:47 PM

I've got this one - 20A but rather heavy. Don't drop it on your toes unless wearing steelcap boots.

Bassnut (Fred) · #11 03-11-2010, 07:15 PM

Quote:

Originally Posted by mswhin63

Battery minimum 80AH

Mains minimum 8A PSU - about the closest I could find in a short time - http://www.jaycar.com.au/productView...T&SUBCATID=647 - enough power at a reasonable cost. Could do one better but at least you now know what to look for.

I hope to have my web sight up soon and supply some of these parts just opening a bank account today,

OH NO, no, this peice of junk comes up again. Its made for testing ONLY (small print in the manual, 5 mins max). It will cook at anywhere near its posted rating if used continuously, even Jaycar cooked one in a shop demo !. I roasted 2 with next to no load before I woke up.

Andrews link is the one I use, its fine. Just dont push it past 50% of its rating.

POwertech supplies are not exactly "industrial", they are made for the bottom end of the hobby market, you pay for what you get, duh

.

mozzie (Peter) · #12 03-11-2010, 07:29 PM

Quote:

Originally Posted by Bassnut

OH NO, no, this peice of junk comes up again. Its made for testing ONLY (small print in the manual, 5 mins max). It will cook at anywhere near its posted rating if used continuously, even Jaycar cooked one in a shop demo !. I roasted 2 with next to no load before I woke up.

Andrews link is the one I use, its fine. Just dont push it past 50% of its rating.

POwertech supplies are not exactly "industrial", they are made for the bottom end of the hobby market, you pay for what you get, duh

.

hi fred
i use one of these power supplies in my pod i bought it from bintel 2 years ago.it is used only to run telescope and corrector plate band and 2" eyepiece band,computers etc run of my 230v power points...
geeezzz i hope it isnt going to overload (cant catch on fire) or something silly like that!!!!!!!

Bassnut (Fred) · #13 03-11-2010, 07:34 PM

Peter

Do yours self a favour, open the box and have a look at the big open coil on the PCB. Is it burnt black, and the PCB around it burnt brown?.

If so expect smoke, soon.

OH, and the jaycar description, " is suitable for use in test and development environments", what does that tell you ?, continuous use?..

mozzie (Peter) · #14 03-11-2010, 07:37 PM

ive just re mounted it on my pier ready for new scope and had it apart to mount and noticed all the boards were fine but ill keep it in mind and may upgrade!!!!
Attachment 83872

Bassnut (Fred) · #15 03-11-2010, 07:46 PM

"All the boards", theres only only 1 from memory, are you sure we are talking the same one? but hey, maybe they improved it over the last 2 yrs, good luck

mswhin63 (Malcolm) · #16 03-11-2010, 10:17 PM

Quote:

Originally Posted by Bassnut

Peter

Do yours self a favour, open the box and have a look at the big open coil on the PCB. Is it burnt black, and the PCB around it burnt brown?.

If so expect smoke, soon.

OH, and the jaycar description, " is suitable for use in test and development environments", what does that tell you ?, continuous use?..

Thanks for the heads up, I dont usually buy much from Jaycar for the same reason, I only read the rated information. Needs more technical information. I am getting more disappointed with them over time, purchaced some torches for conversion and they are cheap as. LED not working opened one up and found very poor soldering technique.

Bassnut (Fred) · #17 04-11-2010, 08:32 AM

Quote:

Originally Posted by mswhin63

Thanks for the heads up, I dont usually buy much from Jaycar for the same reason, I only read the rated information. Needs more technical information. I am getting more disappointed with them over time, purchaced some torches for conversion and they are cheap as. LED not working opened one up and found very poor soldering technique.

Yes, I feel the same. Although generally what they sell is extremely good value for money, especially car audio, over the years quality generally I found has been hit and miss. For example the more specialised low volume Powertech supplies are obviously made as cheap as possible by hand in sweat shops. You have to purchase from Jaycar realising theres a reason for the purchase being cheaper than anywhere else.

mental4astro (Alexander) · #18 04-11-2010, 09:13 AM

Ok, I'm now seeing "the good, the bad and the ugly" on power supply.

To get me by in the short term, a dedicated car battery will do? I'm running out of time to get the good juice for this weekend, and I can get my hands on an auto battery quickly, and cheaply. OK at a pinch? (phrase of the month,

)

mithrandir (Andrew) · #19 04-11-2010, 09:40 AM

Quote:

Originally Posted by mental4astro

To get me by in the short term, a dedicated car battery will do?

A fully charged car battery delivers about 13.5V. My G11 runs happily off one. It also runs happily off the lab supply I listed earlier in the thread.

erick (Eric) · #20 04-11-2010, 10:52 AM

Cheap car battery - yes, it'll get you through one night!

Actually if you don't pull it too low before recharge, you may get some life from it - but don't expect long life. I used one for some months. Last weekend I put it into my car where it will have a happier life. I now have an AGM battery for my astro needs (which are just heaters and Argo Navis).

Traditional vented/flooded lead-acid car batteries are designed to push out cold cranking amps (CCA) to get your car started from cold, then to be recharged immediately and held at charge until the next engine start. They are not designed for lengthy flows of low currents. For our applications we need what are called deep-cycle batteries.

Here are some useful articles:-

http://www.batterystuff.com/tutorial_battery.html
http://en.wikipedia.org/wiki/VRLA_battery
http://www.vonwentzel.net/Battery/01.Type/index.html

After the battery, a good intelligent charger is very important. The el-cheapo charger (like I first bought) may well do damage over time.

I use this one from Jaycar:-

http://jaycar.com.au/productView.asp?ID=MB3606