Second ques. re: tortoise and power supplies.

[Anonymous]

Pls bear with me.

I reposted this from my other post this so it would pop up for a quicker response and help from someone wiser in electronics than I.

 

Is the actual voltage measure of commonj unlimited class 2 supplies  taken into account when the TORTOISE maker says to use 9 to 12 V?

Meantime I have both a 12VDC and 9 VDC power supply handy to try with the three tortoises....however, as you know these ordinary household units are unlimited put out more than they state.....The 12 V reads actually 17V on the meter and the 9 V reads actually 16 V on the multimeter.

[richhotrain]

An electronics expert, I am not.

But the Tortoise instruction sheet is pretty explicit about the maximum power supply.

Here is what it reads in part:

The motor in the TORTOISE is powered continuously and merely stalls out at the end of the throw. The motor will not be harmed by continuous application of 12 volts DC or less. In fact, even if AC is inadvertently applied to the motor terminals , no harm will be done as long as it is 12 volts or less. The TORTOISE will not work with AC , of course, but it will not be damaged.

There are basically three different methods of providing the changeable polarity DC necessary to make the TORTOISE run in both directions.

1. DC WITH CROSS WIRED DPDT SWITCHES: This system uses the most basic power
source, a simple DC supply of not more than 12 volts.

2. BI-POLAR DC WITH SPDT SWITCHES: This system requires two similar DC supplies of
not more than 12 volts each.

3. AC WITH STEERING DIODES: This system utilizes a standard AC Transformer in
conjunction with two diodes to provide half-wave rectified DC to the switch machines.
One side of the transformer output feeds a layout bus wire as in (2) above. The other lead
from the transformer is connected to two diodes, each of which then powers a panel bus
which is connected to the SPDT switches. Note the polarity of the diodes. Only one wire
runs from each panel switch to the respective TORTOISE. Since the system is supplying
only half-wave DC, the voltage of the transformer should be 14 - 16 volts to
compensate.

********************************************************************************************************

I use an MRC Railpower 1370 power pack to power my Tortoises.  I use the DC side of the power pack which has an output of 15 volts according to the spec sheet.

Rich

[Renegade1c]

Most Wall warts are linear power supplies. They put our their max current/voltage all the time and to reduce them down to the 12 volt level you need the proper load on them. They are generally designed to operate with specific electronics (phones, cable boxes, game systems) These are specific loads. On the back it gives a voltage and current rating. For the wall warts to operate properly at those levels you need a load to match which is generally pretty difficult to do.

Instead of using a wall wart which has the problem of over voltage if it has no load (three tortoises is not enough load for most of these supplies) I would suggest getting a switching power supply (similar to a computer power supply) Here is one example: http://www.allelectronics.com/make-a-store/item/PS-12170/12-VDC-1.7-AMP-SWITCHING-SUPPLY/1.html 

A switching power supply is regulated and does not have the over voltage problems that you are experiencing.  It will stay at 12 volts and automatically adjusts when load in increased or decreased.  They may be a few more dollars than your wall warts but the above unit will power a large amount of tortoises (~80) and layout lighting to boot.

[Anonymous]

Thanks very much, Gentlemen.  I know just where to get one of those switching power units.

[rrinker]

 There ARE regulated wal warts - these too will work fine. Switchmode ro linear really has nothign to do with it - cheap wall warts are unregulated, just a transformer, rectifier, and, if you're lucky, a filter capacitor, but usually too small of one. The voltage on one of these will vary GREATLY over the laod range. A regulated supply adds a voltage regulator, or in the case of a switchmode pwoer supply, is already regulated by design. These will vary far less over the range of load capacity. You don;t need a high precision power supply for this purpose, just somethign with some halfway decent regulation.

 Another option is one of the umpteen sellers of eBay with replacement pwoer supplies for laptops and LCD monitors. Some are extremely common. I have a 15V 3amp unit I got for like $6 and it shipped from the US (defintiely made in China, but the seller advertised "ships from the US" and I got it in 2 days).   Different voltages and current levesl are available. Most sellers list the voltage and current, in addition to saying it's for XX brand equipment. Just cut the vendor-specific plug off to expose the wires.

                       --Randy