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Too many volts?


Larfin Frog

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Vitesse MK2. Just fitting an Autosound Vintage 100 dab radio. Works fine through auxiliary position on ignition and though main ignition switch when first starting. But after a mile or so the DAB cuts out and most of the other functions of the radio wont work. Switching off and on while driving does not help! Get home turn it on again and it's fine! Spoken to Autosound, they suggest I may have too much voltage off the dynamo. 

At idle I'm getting 12.5 ish but at higher revs (2,-3000) it topping out at 14.9 ish

 Does this seem too much? If so how to rectify? Any help gratefully received 

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Thats about the right voltage according to the manual settings for the regulator although these are running with the battery disconnected. You must have a good battery that is recharging after a start and the volts then climb to the maximum regulator setting. However even a modern alternator will put out around this voltage as youve got to have sufficient to push current into the battery. You could ask the radio supplier what voltage it can take but yours doesnt sound excessive. It wouldnt be difficult to adjust the voltage down a little in the regulator if thats the only solution....

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Personnally, I would regard that as too high avoltage in hot weather. In my manual, the settings are lower voltage in high temperatures. Either adjust the control box or fit an alternator. The control boxes must be old now and have age ing components.

I set all of my chargers to 13.8 volts for 12 lead acid batteries. Plenty high enough for general use and bulb failure is minimised.

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1 minute ago, Larfin Frog said:

Autosound reckon 14, maybe 14.5 at a push. How would I adjust the voltage down please?

There is a procedure in the Brown Haynes manual. You may find it online, just search fo Lucas RB whatever the nunber is and it should come up.

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Download for free the Triumph GT6/Vitesse workshop manual with all the procedures at vitessesteve.co.uk then remove regulator cover (access not brilliant as up under dash on passenger side) identify the correct one of the three coils and with an appropriate tool rotate the contact adjuster wheel a smidge in the right direction...

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I'd use Colin Lindsay's suggestion, if the higher voltage is not outside normal parameters and it's awkward to adjust the regulator. I'm sure those more knowledgeable above will help if you're going to adjust the control box.

I haven't got experience of dynamo cars, but I do have several integrated circuit voltage regulators in my stores that I could knock up on a piece of veroboard and put into the supply to the radio, which is what I'd do to protect it. If you are not electronically confident in making your own (components required are probably a couple of pounds in total), then there are examples like this available. The three-legged ICs take a varying voltage input and provide a regulated voltage output, up to a certain maximum current. I doubt your radio draws very much, but before going down this route it would be as well to check the figures in the manual. Use a 12V regulator and your radio will probably thank you.

My partner's MGBGT has a resettable 'PolySwitch' cut-out in tandem with a battery isolation key switch for security, so with the battery disconnection switch turned off, the radio clock still functions. However, if the ignition key is turned with the battery off, the fuse blows (it resets itself) so the car cannot be started even though the battery is still connected to the radio.

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The manual has all the info and the hardest bit (apart from access and getting the cover off) is turning the adjuster wheel without the special tool. A drop of penetrating oil on its centre pivot helps and then I use an appropriate size flat blade screwdriver to lever the wheel round a fraction. You can see the three adjuster wheels with their teeth here and certainly a good idea to mark its position before you start...

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3 hours ago, Larfin Frog said:

Many thanks for the replies, and after some googling I think I understand how the regulator works. Will have a look with a more electrically minded friend and see if we feel confident in adjusting, otherwise I like the voltage limiters so may go that route!

Voltage limiters will draw current from the dynamo and could overload it. Far better to obtain the tool and adjust the VR each way until you reduce the voltage to 14v or just under. You can measure this at the battery with the engine running at about 2500 rpm. It needs to settle for half a minute. Sometimes it is quicker with just the sidelamps on. Batteries take a while to drain down with no load.

An alternator kit could be a quicker solution.

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