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Unread 03-08-2009, 12:06
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Sound system Help

Our team's sponsor has recently purchased a car stereo system to put onto our robot for all of our exhibition needs. It is a totally wicked idea, i must admit, save for one problem. I have managed to get most of the system working (I.E. speakers/amplifier) however, the sub-woofer draws too much power from the 12 volt battery itself and just shuts itself off. The amplifier specs can be viewed here: http://www.crutchfield.com/S-1Ib96X1...-MRP-F300.html
and the woofer specs here: http://www.crutchfield.com/S-Nfjbzf1...-SWE-1043.html

I have already tried to hook two batteries in parallel to the system, and that worked a little, yet we still have too much draw. Furthermore, I have looked into amplifier capacitors only to confuse myself with the dilemma of farads. If anyone has any ideas, they would help, Thanks!
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Unread 03-08-2009, 13:02
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Re: Sound system Help

Everett,
It is likely that the power supply in the amp is unhappy. This power supply appears to be a switching supply and can have some pretty high starting current demands. First off, the battery needs to be near the power amp and the cables should be #6 the same as the primary wiring for the robot. (The manufacturer recommends #8 minimum.) The power cables should also be very short, just like the robot. If you are using long or small gauge cables, there is too much voltage drop in the wiring. Large capacitors may help with sudden low frequency demands on the amplifier. The caps listed in the accessories section should be OK but you are spending a lot of money on the LCDs and lights. If you use one, mount the cap very close to the power input on the amp. The amplfier should be turned on with the volume very low as well.
The specifications for the amp in the Crutchfield link says it is intended for 14.4 volt input or the voltage normal car systems might have during battery charge. The manufacturer specs the system at 14.4 volts for distortion and power output. Our batteries are lower at 12 volts nominal but lower dependent on load.
You didn't mention whether you are running the amp in the mono bridged mode or standard stereo. It is unlikely you will need the full power of the bridged mode on a robot cart but the speaker should handle it depending on the enclosure. If you are running in bridged have you followed all the instructions for wiring? I ask because bridged amplifiers cannot have the output tied to battery common. i.e. the output to speaker wiring is different than in standard stereo mode.
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Last edited by Al Skierkiewicz : 03-08-2009 at 13:15.
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Unread 03-08-2009, 17:53
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Re: Sound system Help

Why not do like in some cars and use a second battery. Go to Walmart or autozone and get a marine trolling deep cycle battery. It is not the most attractive idea costwise, but it will handle the power draw. I am not sure what the amp rating on the MK batteries are, but I know a marine battery would have a lot more power. We have a 1000 amp battery for our RV here, and I have been able to run several appliances off it for a year and a half with out recharging.
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Unread 03-08-2009, 20:12
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Re: Sound system Help

The amp is fused with two 25A fuses. The robot battery will happily supply 50 Amps, but not for long, several minutes at most.

A car with the alternator charging is usually at 13.8 volts - 14.4 is a peak maximum (battery damage occurs higher than that). Any lead-acid battery (like the robot battery) can't source more than 12.65 volts*, so you're already at a disadvantage, and under loads like 50 A the voltage sags to 12.2 or less in several seconds (!).

dpeterson3 gives an excellent suggestion: Go to a car store and buy a large marine deep-dischanrge lead-acid battery, and use it power ONLY the sound system, nothing else. Charge it like a robot battery (but it'll take longer), but treat it better, since it contains liquid acid.

Of course, the louder the sound, the more power it needs.

Good luck, let us know what you do.
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