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[ray t]

I have a 12v 500ma charger I use for charging 2 x 6v 7ah batts.  However, I have noticed that it gets quite warm (the charger) to the touch after 20 or so minutes of being switched on.  I measured the output and it reads at just over 19v.  Is this normal for a 12v charger?????

Secondly, I want to be able to charge a 12v 7ah battery in my wireless boat cam rx kit without removing it from the case.  I will be using a phono type socket as my charger has the male side.  Will this cct work???  I will obviously only plug in the charger when the switch if off/open.

[knoby]

I assume you are measuring the charger output with out the battery being connected, in which case its perfectly normal. The charger has to have a higher output voltage when off load in order for it to 'push' the voltage up in the battery when its charging.

The circuit will work fine, although some would advocate using a double pole switch wired so that you can not charge whilst the load is switched on.

cheers Glenn

[treeboa]

i have a bait boat wired similar  way, sealed hull with nimh`s,twin pole on/on switch, one side feeds the battery, the other the the esc`s, that way theres no way you can have the boat turned on while charging, no issues except
mitroniks esc`s and a planet 2.4 sysytem, every so often its had the rx locked out,  mitroniks nor jd perkins is willing to admit theres a problem, removing and replacing the esc lead that feeds the bec reinitialises the rx and its still bound to the tx, three rx`s and two esc`s and its still the same, gone back to 40mhz and no problems

[malcolmfrary]

What knoby said, if the battery is not connected to the charger, it will have a higher voltage.  If the reading is with the battery connected, there is a severe problem.  With many low current chargers, the "regulation" consists of having a transformer wound so that it can only give so much current.  When the load wants to draw more current, it just loses some efficiency, and warms up.  as long as it doesn't heat up beyond the point where the internal fuse (internal to the coil winding, that is) ruptures, getting warm is OK.  Getting hot (where the fingers are withdrawn with a choice oath) is another story.  There might be an actual regulator in there, but usually, these will just dissipate spare energy as heat causing the case to warm up.
The switch is best being a single pole, double contact, or change over type.  Black wire from the socket down to the normally closed contact of the switch.

[dreadnought72]

Perfect timing, Ray!

I have just finished wiring the Racundra in exactly that manner - male tip of phono = +ve, switch just so, etc. Do stick a fuse in before the load, though.

AND I then discovered that my 12v charger similarly spouts 19V when not connected. 

All is good! 

Andy

[ray t]

Thanks for the replys guys.  Will most definately be putting a fuse on the pos side of the load, just forgot to draw it.

@treeboa.  is it a diy bait boat or have you rewired a bought one???

[treeboa]

Thanks for the replys guys.  Will most definately be putting a fuse on the pos side of the load, just forgot to draw it.

@treeboa.  is it a diy bait boat or have you rewired a bought one???

both mate, did a rework on an at boat earlier in year, radio gear totally boolarxed , plus a cat i recently purchased part built thats a sealed hull and carries a 7.2 5ah nimh pack and twin graupner jet drives