GO - DIY Power supply

bestyman · Posted: Mon Sep 27, 2004 7:03 pm Post subject: So far so good.

Hi all,
I assembled all the parts put them in a plastic box and checked the voltage which was 4.9volts, just slightly lower than the tom tom go lead but near enough for me.

I connected the TTgo and guess what......IT WORKED !

I then connected it to the car supply and was about to tie wrap the unit behind the glove box when I realised it was a little warm...well hot . Now I realise that voltage regulators do get warm (ish) but I was a little paranoid so time for a rethink.

Back at maplins the options were to buy a heatsink or mount the unit in a metal box. I choose to mount it in a metal box for 2 reasons, the first a larger surface area to disperse heat and most importantly metal boxes are fireproof. I simply drilled a hole in it and mounted the voltage reg to the metal box. The metal box is only lukewarm after 20 minutes and I feel confident all will be well.

If anyone is thinking of making one most of the parts have already been mentioned apart from a 4mm power plug and a lead , both available from Maplins. If I knew how to post a diagram on here I would so perhaps someone can tell me or if you need a diagram drop me a message.

I will keep an eye on things over the next few days but so far I am chuffed with it .

Lastly, If yo do choose to make one and your TT go blows up and your car catches fire please dont blame me because afterall I am only a Plumber so follow my advise, or should I say experiments at your own risk. As it says on the instructions if in doubt consult a qualified electrician :D

Regards

Mark

ps If it did blow up Im sure I would tell tom tom that it was all my fault Wink

metroman · Occasional Visitor Joined: Dec 14, 2003 Posts: 18

Nice one Mark. You've created quite a lot of interest with this thread. Did you take any pictures? Also what type of car is it that you have? metroman.

Old_Phil · Posted: Mon Sep 27, 2004 7:41 pm Post subject:

Well done Mark :D I'd be interested in seeing some pics as well.

bestyman · Posted: Mon Sep 27, 2004 9:14 pm Post subject: still ok

Hi,
Yes I will take some pictures , but can anyone please tell me how to post them here? Do I have to upload them to a website first?

The van that I fitted it in was a vauxhall astra. The unit itself is secured on the dash by self adhesive velcro strips on the dash amd on the bottom of the TTgo. May sound a bit of a bodge but works perfectly and the GO can be removed and fited with ease( unlike when using the supplied bracked)

I failed to mention in my last post that the unit was wired to an ignition live so at least if it does overheat Ill be there to put it out !

Regards

Mark

awdriver96 · Occasional Visitor Joined: Jan 02, 2005 Posts: 18

I have seen plenty of talk of fried tomtoms on other sites too. I am an electrical type and have thought on this a bit. firstly Marks device will work but may cause problems due to poor regulation and noise from the regulator itself. If I was making one and I may do so, I would use an LM 317T which is a 4 amp device and incorporate a crowbar circuit with 2 amp fuse into the output, then if it goes tits up it will blow fuse and save little TomTom.
The trouble with the fag lighter thing with TTG is that the fuse protects the car circuit not the TTG hence the frying sounds followed by death!
Mike

bestyman · Posted: Mon Jan 10, 2005 11:19 pm Post subject:

HI,
Tomtom now sell separate leads on the website for about a tenner I think, but they didn`t sell them at the time I built mine.
Think I might invest in one!
Mark

epideme · Occasional Visitor Joined: Mar 30, 2004 Posts: 2

One tiny remark on the LM317 series regulators compared to the 7805 series.

The 317 is a variable regulator, which allows setting the voltage using a couple of resistors on the adjust pin. Even though the T model may supply more amps the 7805 is a better choice in my opinion. Why?

If one of the resistors in the LM317 design break you may end up feeding the output with too high voltages. Fatal if you're an expensive GPS thingie.
The 7805 is designed for 5 volts only and seem more secure to me.
Both LM317 and 7805 is internally heat- and overload protected so that is really no problems in that department.

Be VERY aware that the LM317 must NOT be grounded through the heat sink. The heat sink is always connected to the center pin on almost all TO-220 type components.

The 7805, on the other hand, can be grounded through the heat sink so it is theoretically possible to mount it with a screw to the car chassis to dissapate some heat and get more power from it.

Take care dudes and don't blow anything up.

dux · Occasional Visitor Joined: Feb 12, 2005 Posts: 3

I also don't like the wires from the cigarette lighter. Instead of building a regulator I simply used the supplied unit. After a few trials the simplest solution is to solder wires to the central pin (+ve) and side connection (-ve). These can then be spliced into a convenient positive (via a glass fuse) in the car and earth for the -ve.
I've done this in three cars so far; Nissan Micra, Rover 211 and Peugeot 307 (which also needed an external antenna). Although a bit fiddly there has always been somewhere to hide the regulator and wiring. In one case I used Maplins equivalent of the Tom Tom regulator ie would normally be plugged into the cigarette socket, this unit happens to have a built in fuse, and this unit has also worked fine.
Obviously there are choices on the +ve connection whether switched via the ignition or a permanent live, on balance a switched +ve is probably a better choice.

Skippy · Posted: Sun Feb 13, 2005 12:37 pm Post subject:

You shouldn't use a 317, you would have to manually set the voltage which is dangerous. The 7805 is a good regulator and it's fixed voltage it's bomb proof.

The comments about the 7805 being "noisy" and having "poor regulation" are completely untrue. They offer extremely good regulation and stability and they are virtually indestructable with thermal cut out and short circuit protection.

Read the datasheet if you don't believe me... Rolling Eyes

And to all the people who say you will fry your TTG. Go out and pay £30 for the same thing. :P
_________________
Gone fishing!

awdriver96 · Occasional Visitor Joined: Jan 02, 2005 Posts: 18

If you know enough to use a 317t then you should have no problems setting voltage and if you read my post in full i said that a crowbar on the output should be used, then there is no risk. The 7805 is fine but only 1.5A continuous. ther used to be a 7805h in TO3 case but this seems to be no longer supplied. The noise and regulation issue is real, if you know about psu design you would know that the smoothing caps are not just there to fill up the box but , provide smoothingand filtering. then you also need a more substantial crowbar device to take the current delivered by the caps until the fuse goes. i have built a couple since the original posting and they work ok, but rather than s fuse i have used a high speed mcb instead.

Skippy · Posted: Fri Mar 25, 2005 12:41 am Post subject:

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