connecting my drill nicad to the gell battery

[simonfraser]

my 12V gell boat battery is empty = 12.0V
being lazy here and knowing the wind/solar will sort it out in a week or so:

i have an 18V battery pack for the portable drill.

that will have enough in to drive my autohelm for a few hours for a solo sail on sunday.

so how about connecting the nicad pack to the 12V battery, that should give it enough of a boost to work ??

comments please before i blow the lot up

 

[andy01842]

blow it up

my 12V gell boat battery is empty = 12.0V
being lazy here and knowing the wind/solar will sort it out in a week or so:

i have an 18V battery pack for the portable drill.

that will have enough in to drive my autohelm for a few hours for a solo sail on sunday.

so how about connecting the nicad pack to the 12V battery, that should give it enough of a boost to work ??

comments please before i blow the lot up

I can say with confidence you will almost definitely blow it up. both battery have very low resistance and with a 6 volt difference the amps will be very high!

 

[pampas]

I have a cheap Callenge 14.5v, battery duff. Opened up and soldered to the incoming terminals(Not directly to the battery) with a long enough lead to reach the whole boat inside and out. Found it gave me more power than when new but top speed is down a bit.

 

[simonfraser]

if i put a 12 light bulb in series to create a resistance i might be ok ?

 

[VicS]

if i put a 12 light bulb in series to create a resistance i might be ok ?

yes good idea. I was going to suggest a resistor of a few ohms but it'll need to have an adequate power rating.

25 watt navigation light bulb or a car stop or flasher (21 watt) or a head light bulb for a bit more current.

 

[simonfraser]

tnx, i've got a 20W ceramic resistor, i'll put that in.
sunny and 10knots sunday, that's gota be done

 

[William_H]

Resistor

You don't say what resistance your 20w ceramic resistor is. They can be had from .1ohm up to several thousand ohms. The resistance will dictate the current that flows from the 18v battery into the 12v battery.
So given a 4 to 6 volt difference of battery volts. A 1 ohm resistor will limit the current to 6 amps reducing to 4 amps. hat is probably Ok to decant the drill battery into the gell battery.10 ohms would be a bit slower (safer) Bearing in mind the drill battery might be good for say 2 Amp hours which you may get into the gel battery. But is that enough? good luck olewill

 

[simonfraser]

indeed, it's a 2A one, decant, that's a good description

 

[VicS]

As Will says you do not say what the resistance is. That is the important factor.

something between 2 and 10 ohms makes the idea a goer but if more than 10 rather slow to "decant" the charge. Much more then much slower

 

[simonfraser]

2A 20W resistor used, it did the trick.
11.90 before connection.
12.8 at first on connection.
lasted about 2 hrs, drill nicad capacity 2.3Ah (18V), so that figured.
then dropped down to 12.1 after 5hrs.
so it sorted the autohelm, which is what i needed.

tnx for the tips.