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Checking ampherage draw

Old 11-15-2007, 06:05 PM
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Default Checking ampherage draw

Can I use a cheap automotive amp gauge (like what comes in the oil press/water temp/amp 3 gauge set) in line of the + battery cable to check for total draw the battery sees while running stereo amps, lights and such? Trying to determine the size of an onboard battery charger needed to keep up with the draw.

Or is it not that easy? My multi tester is only rated for 10amp max. So no go.
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Old 11-15-2007, 08:20 PM
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Yep. That's what they do. Pull the alternator field wire so you're getting only demand, not supply. You'r reading won't be too accurate but you'll be within a few amps.

The gauge goes between the main feed to your fuse block, not in-line between the battery and the primary cable that runs to the starter.
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Old 11-15-2007, 09:48 PM
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This is for testing while the boat is in the slip and on the charger and jamming on the dock and maybe the cabin lights on. So motors are off. I rarely run the stereo on the water for much more than a few minutes. In that case, can I simple connect right at the battery?

Been having trouble this summer with house battery always being low to the point of the amps shutting down. Battery was new this spring. 1000 CCA dual purpose. Battery will be tested, but also planning on upgrading my 10 amp charger if need be.

Thanks
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Old 11-16-2007, 06:13 AM
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For a test, sure- just go inline between the terminal and the cable. If you try to crank it will fry the gauge. Prior to your test, take a test light and hook it up in-line as you would the gauge. Make sure everything is off but the battery disconnects are on. if there's a current drain, the battery will light. It might just barely light if the draw is slight. You can also do this same test with a volt meter in-line. This will tell you if you have a current drain that's slowly killing your battery. If you have EFI motors, you'll have to un-plug the ECM- it draws a tiny bit of current at rest.

If your charger works, it's plenty for keeping the batteries fully charged. The only reason to use a bigger unit is if you're in a hurry. 10 amps will warm one up overnight if it had enough to crank the motor the day before. Fast charging is bad for all batteries if done repeatedly. I'm not a huge fan of dual-purpose batteries. If you need one, you probably need a dedicated deep-cycle on an isolator. You can get a nice box for $100, the batt for $75 and the isolator for about the same. Then you can suck it dry and still start the boat. You can also toss a set of jumpers in your anchor locker and bail yourself out if your main battery shorts a plate from all that bouncing around.
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Old 11-16-2007, 05:33 PM
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Originally Posted by Chris Sunkin
For a test, sure- just go inline between the terminal and the cable. If you try to crank it will fry the gauge. Prior to your test, take a test light and hook it up in-line as you would the gauge. Make sure everything is off but the battery disconnects are on. if there's a current drain, the battery will light. It might just barely light if the draw is slight. You can also do this same test with a volt meter in-line. This will tell you if you have a current drain that's slowly killing your battery. If you have EFI motors, you'll have to un-plug the ECM- it draws a tiny bit of current at rest.
Thanks.
Yes, testing is just for while docked referencing only. Just a check to see what draw each item has for a baseline.
I did do the test light last summer. With my stereo amps off, both (independently) would make the test light flash. Never would go off. Was told because of the capacitors in the amps.
An dedicated deepcycle battery has been considered for house use, with 2 starting batteries for the motors. Just seems eccessive to have 2 batteries just for starting the motors, hence the reasoning of the dual purpose one.
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Old 11-18-2007, 08:15 PM
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Originally Posted by US1 Fountain
Thanks.
Yes, testing is just for while docked referencing only. Just a check to see what draw each item has for a baseline.
I did do the test light last summer. With my stereo amps off, both (independently) would make the test light flash. Never would go off. Was told because of the capacitors in the amps.
An dedicated deepcycle battery has been considered for house use, with 2 starting batteries for the motors. Just seems eccessive to have 2 batteries just for starting the motors, hence the reasoning of the dual purpose one.
dont forget to post what ya find
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Old 11-18-2007, 08:28 PM
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Originally Posted by offthefront
dont forget to post what ya find
I think they will show I haven't the slightest idea of what the hell I'm doing.

Yesterday I unhooked the + cable, hooked my Fluke meter in series between the battery and the disconnected cable. Set to10A setting. Flipped the power switch on to power up the cabin. Nothing happened. Not even the indicator light would light up showing the cabin power was on. Meter showed nothing. Touched the main battery cable to the battery, power came on. I assume the meter won't act as a pass thru?
Haven't picked up an car amp gauge yet. Just piddling with the meter and the small current draw stuff 1st getting an idea.
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Old 11-18-2007, 08:55 PM
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Just describe what kind of stereo you are running. Lots of amplifiers/subs and what not, you need a pretty big charger. One sub, a few lights, and what not, maybe a 20 amp will do, the battery will fill in the low spots when draw is a little more, and recharge when less.
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Old 11-18-2007, 09:04 PM
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Originally Posted by US1 Fountain
I think they will show I haven't the slightest idea of what the hell I'm doing.

Yesterday I unhooked the + cable, hooked my Fluke meter in series between the battery and the disconnected cable. Set to10A setting. Flipped the power switch on to power up the cabin. Nothing happened. Not even the indicator light would light up showing the cabin power was on. Meter showed nothing. Touched the main battery cable to the battery, power came on. I assume the meter won't act as a pass thru?
Haven't picked up an car amp gauge yet. Just piddling with the meter and the small current draw stuff 1st getting an idea.
in most test meters like the Fluke you have to put the probes into different plugs on the meter to test DC current ...not the same as the settings for dc or ac voltage ... your right that the meter needs to be in series to test DC amps .. Even if its a "clamp on" type meter I think that will only apply in a "ac" circuit ...The do make a clamp on DC tester but I dont think a standard type clamp on will show DC amps ....m
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Old 11-18-2007, 09:22 PM
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On the flukes, there is a fuse that protects the 10 amp circuit. If your draw is more than that, you need to use a clamp meter (CT) to check the draw.

Open up the back of the meter to find the 10 amp fuse, and see if its blown.
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