Power for VHF

[Spuddy]

While mast is down I'm checking on why radio doesn't work. Thought I'd power up the set in kitchen and rather than disconnect car battery I used a battery charger. No joy and charger only shows 0.18V between + and - . So is charger no go as an alternative source of 12 ish volts because of its design, or has the charger had it ?

 

[philip_stevens]

The battery charger may need a battery connected to get the output voltage.

The one I have on the boat requires the battery to be connected before I get an output.

 

[srp]

Most power supplies need a load connected if you're going to get an accurate voltage reading from them. Some power supplies (eg switch mode supplies as used in computers) HAVE to have a load connected before you power them up otherwise you risk serious damage.
A sophisticated battery charger may regulate the output according to the batterys internal resistance, which may account for the low output with no battery connected. A cheap battery charger will probably show a high voltage on the output with nothing connected.

 

[Spuddy]

Thanks gents. I'll raise the bonnet tomorrow and use car battery.

 

[GrahamC]

Its not a good idea to key the transmit switch without an ariel connected, a cheap ariel can be nade by stripping backa about 2 feet of co-ax cable and taping it to a stick, Inner core one way and the coax cover the orher, a simple dipole is the result that works quite well, 20ft of cable should be fine, or buy an emergency ariel but you must have one in circuit if you are going to transmit
Regards
GrahamC

 

[shamrock]

Had the same problem testing 12v equipment and quickly realised that a battery was needed in circuit because the charger senses the VHF or whatever as a full battery and knocks back the charging accordingly.

Went to the local dump (sorry, recycling centre) and they have a batteries bin, in which I found a set of five small sealed 12v batteries about 6x3x2 inches with spade connecters. The guys at the dump swapped them for 5 of my grubby pound coins.

These have turned out to be really useful, as I keep a couple of them charged up on board in a locker, and if I need to test something before wiring it in, or if I am fault finding and want to check the 12v supply, I can put one of these anywhere.

You can also buy them from maplin for about 15 quid each. 12v sealed battery