# Swapping batteries for Fish Finder

Discussion in 'Power Electronics' started by cliffspab, Oct 9, 2014.

1. ### cliffspab

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0
Oct 9, 2014
Hi, I bought an old Sonar Fish Finder that I want to use for ice fishing. I don't want to lug around a full size marine battery. Which 12 volt batteries could I use without damaging my Fish Finder or blowing lots of fuses? Here is some info on the fish finder, Voltage- 12 volts (operates 10-15 volts), Current Drain- 175 ma, one echo, Frequency- 192 khz, Pulses Repetition- 40 pulses per second, Pulse Width (adjustable)- 200-1000 micro seconds, Output Power- 200 watts p-p typical (25 watts rms).
Any information would be appreciated.
Thanks

2. ### Colin Mitchell

1,418
314
Aug 31, 2014
How long do you want the fish finder to operate for?

3. ### Harald KappModeratorModerator

9,659
2,019
Nov 17, 2011
Welcome to our forum.

Any 12V battery should do.
As for endurance: Your numbers do not match. At 12V*175mA the average power input to the fish finder is 2.1W. It therefore cannot emit 25W RMS.
Assuming that the 25W RMS are for the active period of the signal only and further assuming that the input current to the fish finder is more or less constant at 175mA (peak current for the high-power pulses probably provided by internal bufffer capacitors), the lifetime of a battery can be calculated by:
T (in hours) = capacity (in Ah)/0.175A
You should factor in some allowance for deteriorating battery capacity due to lifetime, temperatire etc. Using a factor of 0.8 you arrive at
T (in hours) = capacity (in Ah)/0.175A*0.8 or equivalently T (in hours) = capacity (in mAh)/175mA*0.8

4. ### cliffspab

2
0
Oct 9, 2014
I has hoping to hook up a rechargeable battery that would last a day of fishing, 4-6 hrs. Ya, my electrical knowledge is limited. Its been many years since I took electronics and physics classes in highschool. The info for my sonar fish finder that I gave is what was in the owners manual. I appreciate the help.
Thanks

5. ### Gryd3

4,098
875
Jun 25, 2014
Well. Using Harald's formulas above:
6H = Capacity / 0.175A * 0.8
Capacity = 6H * 0.175 / 0.8 = 1.3Ah or 1300mAh
Take a look at some batteries to see what you can find with that kind of capacity.
(Batteries used in many home backup battery systems are about 8Ah, and some alarm backups are about 1.3Ah. So take a peak at some Sealed Lead Acid batteries and pick one that suits your fancy)