Power Input For Vista C

[ulloobata]

Hi,

 

I purchased a Visata C few weeks back. The local dealter here in Saudi Arabia don't have a car ciggerate lighter adopter for it and I am using rechargable batteries since then. I was planning to custom make a car adoptor for my GPSr from a moible phone car charger.

Can someone tell me what is the maximum/minimum DC voltage Vista C can take without burning it?

 

Any help is highly appriciated.

 

Chaudhry

[+park2]

Be careful. With my Vista (not C), it was only 3 or 5 volts (can't remember exactly), not the full 12V that my old 12 or new 76CS would take. That is why the lighter plug is so much bulkier, there is a voltage regulator in it.

[Vlad]

hmm not sure offhand - check the specs page of the unit's owners' manual - all are available on www.garmin.com

[ulloobata]

Thanks park2 and Vlad.

 

Vlad: The manual says power source: "Two 1.5 volt AA batteries or 12V Adaptor Cable"

 

12V Adaptor Capble part is the one I want to be sure about.

Vista C can take power from USB port While connected to a PC. USB port has 5VDC output, which means it can work at least on 5VDC.

I am unable to find any mobile phone adaptor with less than 7.5VDC output or car adaptor with USB output.

I just want to be sure before I connect it to some wrong power source.

[Neo_Geo]

Vlad: The manual says power source: "Two 1.5 volt AA batteries or 12V Adaptor Cable"

The "12V" in "12V Adaptor Cable" is refering to INPUT voltage - meaning 12 volts going from the car's electrical system into the cable. The output voltage could possibly be 12 volts as well, but more than likely will be much less. The serial (RS-232) cables for the b&w Legends & Vistas and the 60 series GPSrs all have cables which have an output of 3 Volts. Since those units take two 1.5V (3 volts total) batteries, it stands to reason that the Vista C would operate on 3 volts as well.

 

Now - I don't know a thing about pinouts and standards for USB. Is it 5 Volts output from the USB cable into the USB device? I will leave this question for others to research. If so, then you have to regulate the 12 Volts going into the cable, down to 5 Volts output (with the GPSr's internal circuitry regulating the extra 2 Volts).

 

Bottom line is that you have to reduce the 12V going into the cable to whatever is the standard output voltage of a USB connection. Basically this involves getting 2 resistors of different resistance values (Ohms). The values in question would be determined by knowing how much current (Amperes) flows through the circuitry. This could also be dermined by knowing how much power (Watts) they consume.

 

Use below theory AT YOUR OWN RISK!!!!

 

Can we determine these values by the battery life? If we have two batteries which hold a charge of 2,100 milli-Amp hours each (for a total of 4,200 mAh), and they typically last for 15 hours... then 4,200 divided by 15 would be... 280mA or 0.28 Amps. I dunno - sounds good to me...

 

Now let's look back at Ohm's Law: V=IxR (Voltage = Current times Resistance)

12 = 0.28 * Resistance

or

R = V/I (Resistance = Voltage divided by Current)

R = 12/0.28

R = 42.85 Ohms total

 

You would need a 40 to 45 Ohm resistor if you wanted to have a cable with a 12V output. To get 5V output, you have to have two resistors - a 25 Ohm, and an 18 Ohm resistor. Then build your cable's + and - across the 18 Ohm resistor.

 

Does anybody concur or disagree?

Edited November 28, 2004 by Neo_Geo

[peter]

Use below theory AT YOUR OWN RISK!!!!

 

Can we determine these values by the battery life? If we have two batteries which hold a charge of 2,100 milli-Amp hours each (for a total of 4,200 mAh), and they typically last for 15 hours... then 4,200 divided by 15 would be... 280mA or 0.28 Amps. I dunno - sounds good to me...

 

Now let's look back at Ohm's Law: V=IxR (Voltage = Current times Resistance)

12 = 0.28 * Resistance

or

R = V/I (Resistance = Voltage divided by Current)

R = 12/0.28

R = 42.85 Ohms total

 

You would need a 40 to 45 Ohm resistor if you wanted to have a cable with a 12V output. To get 5V output, you have to have two resistors - a 25 Ohm, and an 18 Ohm resistor. Then build your cable's + and - across the 18 Ohm resistor.

 

Does anybody concur or disagree?

No, don't use it at anyone's risk. You need to hold the input voltage to the VistaC fairly constant at 5 VDC consistent with the USB spec. But the voltage at your nominal 12 VDC car power outlet can vary considerably depending on what your alternator puts out and any pulses generated by other devices in the car. Just putting a fixed resistor in series can't keep a constant output voltage when the input voltage is changing. The other problem is that the current drain by the VistaC won't be a constant value either - the backlight can be on or off, same with the compass, the processor can have periods with higher and lower current drain, and even the radio circuits can be turned off for periods of time to save power. With just a fixed resistor to drop the voltage, the changing current draw of the VistaC will result in varying the effective input voltage.

 

So what you need is to include a voltage regulator that'll put out a regulated 5 VDC regardless of changes in the current drawn by the VistaC.

 

BTW, there are also a few problem with the calculations quoted above. The two cells are in series, so the same current flows through both. Therefore you should use the 2100 mA-hr capacity divided by the hours of use to get the average current. With a stated battery life of 20 hours, this is just a little over 100 mA rather than 280.

Also, the resistor would be dropping the difference between the input voltage (nominally 12) and the input to the VistaC (5 V), so you'd want to have 7 V across the resistor rather than the full 12 V.

 

But again, you really want a true voltage regulator, not just a simple series resistor to protect the VistaC from the wrong voltage. If you're not completely sure that you can get a good regulated 5 VDC into the USB connector on the VistaC, I'd recommend that you continue to use rechargeable cells and get a battery charger to keep in the car that plugs into the 12 VDC outlet. Keep one set of cells charging and one set in the VistaC.

[vr12]

Does Vista C uses the same power cable 60CS uses ?

if so then I think it can accept 12 volts

 

Or you are trying to power it via USB ?

I wouldn't recomend 12 volts through USB connector.

....

I looked at manual, it powered through USB connector. which means it accepts 5 volts and unless you know for sure you shouldn't try 12 volts.

Edited November 28, 2004 by vr12

[vr12]

I am unable to find any mobile phone adaptor with less than 7.5VDC output or car adaptor with USB output.

I just want to be sure before I connect it to some wrong power source.

If you familar with soldering you can easily adjust output voltage on cell phone adaptors.

[+EScout]

 

If the Vista/Legend C take a charge from a USB port's 5V DC, then get one of the cig lighter plugs with a USB port. I got one from Belkin and it has a regulator and outputs 5V. I use it to charge my Sony PDA using its USB cord, in the car. I found this cigt lighter plug at the 99 Cents Only Store with some cell phone USB cord. Just throw away the cord and keep the plug.

 

The store also had a Wall-wart with a USB port that you can use to charge devices using AC wall power. It is a nice light-weight cube with an LED, regulated switching power supply. Printed on it: Input 100-240VAC, 50-60Hz, Output: 5.5V, 6W.

Edited November 28, 2004 by EScout

[Vlad]

i would recommend sending an email to garmin (support@garmin.com) and asking them about the max input voltage the unit can handle.

 

3 to 5 vdc would be my guess - based on the older etrex units i'm more familiar with.

 

i'll take a look at one of the garmin usb power adapters to see if it indicates an output voltage anywhere on it.

[ulloobata]

vr12: You got it right, it has a USB connector. I am not much familar with soldering thing so I won't probably try that

 

Escout: I wish to find this car adopter here in Saudi Arbia, but still not luck with that.

 

Vlad: I am just going to mail them.

 

Thanks every one for your valued input.

Edited November 29, 2004 by ulloobata

[+EScout]

PDA Adaptor on Ebay

 

Look at the cig plug with this item. It is similar to mine. Outputs 5V at up to 400 mA. Check to see if the 400 mA is sufficient current to run your Garmin. There are probably hundreds more similar charger deals on ebay for various items. Try to find one that charges your PDA or cell phone (those with a Li-ion battery of 3.7V)

[Vlad]

confirmed today - garmin's spec as stated on the cig adapter/usb for the legend c and vista c is 5 vdc output at 1 amp.

[ulloobata]

Thanks a lot Vlad, this answers my question.

Thanks everyone for your help I really appricate your input.

 

Here is the reply I got from Garmin:

 

"Thank you for contacting GARMIN International.

 

I would be happy to help you with this. The Vista C will use within a

range

of 4.2v to 5.5v depending on the processor speed used for what you are

doing

at the time of power from the USB connection to the pc."

 

Best regards.

Edited November 30, 2004 by ulloobata

[Dukie 'n' Dad]

To Markwell, this was talked about here:

 

Vista C Power