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Hotpants
Occasional Visitor
Joined: May 25, 2005
Posts: 20
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 Posted: Mon Dec 26, 2005 4:54 pm Post subject: |
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Season's Greetings to one and all. Hope you all had a peaceful and enjoyable Christmas.
Went to Woolies today to pick up the PSP USB data cable and charger. Woolies didn't stock the official PSP one, but had one made by a Company called VGA (Video Game Accessories) for £3.99.
Result - one charging TT ONE as I speak 
Cheers
Hotpants |
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Buffy Beagle
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Joined: 04/03/2003 21:22:30
Posts: 191
Location: United Kingdom
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| Posted: Tue Jan 24, 2006 4:44 pm Post subject: |
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Some time ago Victor123 wrote:
That item (which is now advertised at £4.95) appears to be rated for 500 milliamps at 12 volts whereas the TomTom One charger is specified as supplying 2 amps at 5 volts. If I remember my physics correctly 2 amps at 5 volts equates to 833 milliamps at 12 volts. Is it really OK to use the Car Charger Converter (perhaps because the TomTom One in fact draws only 1.2 amps or less at 5 volts)? If the TomTom One does draw more current than the Car Charger Converter is rated for what problems can be caused? Presumably the TomTom One could not be damaged, and perhaps the worst that could happen would be that the Car Charger Converter might be fried.
Hugh |
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Oldboy
Pocket GPS Moderator
Joined: Dec 08, 2004
Posts: 10641
Location: Suffolk, UK
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| Posted: Tue Jan 24, 2006 8:14 pm Post subject: |
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| Buffy Beagle wrote: | | If I remember my physics correctly 2 amps at 5 volts equates to 833 milliamps at 12 volts. |
It would be the case if the voltage was 'transformed'. However the voltage is controlled by a Voltage Regulator.
This means that if there is 2A being drawn at the 5V there will also be 2A being supplied at the 12V input. The Regulator is dropping the 7V difference and at 2A would be dissipating 14W of heat.
_________________
Richard
TT 910 V7.903: Europe Map v1045
TT Via 135 App 12.075: Europe Map v1120 |
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Buffy Beagle
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Joined: 04/03/2003 21:22:30
Posts: 191
Location: United Kingdom
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| Posted: Wed Jan 25, 2006 12:01 am Post subject: |
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Thank you, OldBoy, for your reply.
Does this mean that the mains to 12 volt DC adapter would need to be rated at 2 amps in order to be used to charge the TomTom One?
What would happen if TomTom One tried to draw 2 amps from a charger rated at 500 milliamps? Could we damage anything other than the charger? Could it cause a fire? How great is the risk? If we could only damage the charger and the potential damage is slight then perhaps that is a risk worth taking if the charger only costs £5.
If Victor123 is still reading this thread it would be interesting to know how he (or anyone else who bought a mains to 12 volt adaptor) has got on with it.
Thanks for your help. |
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Oldboy
Pocket GPS Moderator
Joined: Dec 08, 2004
Posts: 10641
Location: Suffolk, UK
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| Posted: Wed Jan 25, 2006 8:19 am Post subject: |
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| Buffy Beagle wrote: | | Does this mean that the mains to 12 volt DC adapter would need to be rated at 2 amps in order to be used to charge the TomTom One? |
The 12V DC Output would need to be rated high enough.
| Buffy Beagle wrote: | | What would happen if TomTom One tried to draw 2 amps from a charger rated at 500 milliamps? Could we damage anything other than the charger? Could it cause a fire? How great is the risk? If we could only damage the charger and the potential damage is slight then perhaps that is a risk worth taking if the charger only costs £5. |
I think the main problem would be in the charging cycle. I don't know how this would affect the life of a Lithium Ion Battery if a Flat Battery was charged at a less than optimum rate.
The risk of fire, etc. would be down to what protection was placed in the unit. If the unit goes short-circuit, and not open-circuit, then there could be problems. TT wouldn't want to know then.
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Richard
TT 910 V7.903: Europe Map v1045
TT Via 135 App 12.075: Europe Map v1120 |
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Buffy Beagle
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Joined: 04/03/2003 21:22:30
Posts: 191
Location: United Kingdom
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| Posted: Wed Jan 25, 2006 11:36 am Post subject: |
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| Quote: | | The 12V DC Output would need to be rated high enough. |
I'm afraid I find this very confusing. How high is "high enough"? 500 milliamps? 2 amps? Or something else? How much current does the TomTom One actually draw? |
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sitrap
Lifetime Member
Joined: 14/05/2003 21:10:49
Posts: 33
Location: Barnsley, UK
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| Posted: Wed Jan 25, 2006 11:56 am Post subject: |
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| Quote: | | The 12V DC Output would need to be rated high enough |
8O  STOP - Do not use a Mains to 12V ac adaptor. TomTom uses 5V. (5 volts) You are going to damage your Tomtom.
To use an old analogy. Electricity v Plumbing. Current (amps) is the volume of water flowing thru the pipes (wires) Volts is like the water pressure - too high and the pipe will burst. Watts is like the power pushing the water thru the pipe. So if you raise the power or the amount of water the pressure (or volts) will increase. The pipes ( or wires) have a finite capacity, and if you go too high on your volts, the pipes will burst (wires will melt) |
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sitrap
Lifetime Member
Joined: 14/05/2003 21:10:49
Posts: 33
Location: Barnsley, UK
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| Posted: Wed Jan 25, 2006 12:19 pm Post subject: |
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Ok - guilty - I didn't read back down the thread far enough - I was just concerned you were oing to use 12V straight into the TomTom - As you were.  (crawls off into a quiet corner) |
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Oldboy
Pocket GPS Moderator
Joined: Dec 08, 2004
Posts: 10641
Location: Suffolk, UK
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| Posted: Wed Jan 25, 2006 8:11 pm Post subject: |
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| Buffy Beagle wrote: | | I'm afraid I find this very confusing. How high is "high enough"? 500 milliamps? 2 amps? Or something else? How much current does the TomTom One actually draw? |
I don't know if the ONE uses the same battery as the Classic, but if I remember correctly when the battery is nearly flat it can draw in excess of 800mA. So if 500mA is only available the Charge Rate would not be optimised.
The 2A capability gives the Charger a margin of tolerance.
If you want some in-depth reading on Lithium Ion Batteries I recommend the website at http://www.batteryuniversity.com/
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Richard
TT 910 V7.903: Europe Map v1045
TT Via 135 App 12.075: Europe Map v1120 |
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Buffy Beagle
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Joined: 04/03/2003 21:22:30
Posts: 191
Location: United Kingdom
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| Posted: Thu Jan 26, 2006 10:45 am Post subject: |
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| Quote: | | if 500mA is only available the Charge Rate would not be optimised. |
Thanks for all your help. I'm afraid we're still not clear what this means. Will the charger (when used in conjunction with the in-car adapter supplied by TomTom) somehow limit the current to 500mA and therefore not supply as much current as the GPS unit might sometimes like to draw, with the result that charging might take longer but no damage can be done? Or does it mean that the GPS will draw more current (up to 800mA) than the charger is designed to deliver, so damage could result?
I've tried reading the Battery University page on charging lithium ion batteries ( http://www.batteryuniversity.com/partone-12.htm ). It sounds as if the answer to these questions may be that it depends on the design of the charging circuitry built into the GPS unit.
In view of the uncertainty it sounds as if we should advise our friend to ignore the Mains to 12v DC adapter (rated at 500mA) and go for a Mains to 5v DC adapter which is rated at 2 amps or more. |
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BillyHey
Lifetime Member
Joined: Jan 05, 2006
Posts: 25
Location: Linlithgow, West Lothian
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| Posted: Thu Jan 26, 2006 4:53 pm Post subject: |
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I didnt' get free delivery when I ordered one a couple of weeks ago - and I got the pleasure of being woken up by the postie on a Saturday morning at 0700! |
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poppy10
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Joined: Feb 23, 2008
Posts: 7
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| Posted: Sat Feb 23, 2008 2:06 pm Post subject: |
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| Can I just check then - I have a mains charger that is rated 5V 500mA - will that work OK for my TomTom One v1? |
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mikealder
Pocket GPS Moderator
Joined: Jan 14, 2005
Posts: 19638
Location: Blackpool , Lancs
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| Posted: Sat Feb 23, 2008 2:16 pm Post subject: |
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| It will be fine for charging the unit although it will take a while - Mike |
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