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.

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.

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

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.

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 :drink:

I think they will show I haven't the slightest idea of what the hell I'm doing. :D

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.

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.

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

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.

Sony DVD head unit,
JL Audio 300/4 amp
JL Audio 250/1 amp
Cabin has both rope style lightsfor lack of better descriotion, and several flouracent (sp) tube lights.
Sharp 13" flatscreen TV

on board 10 amp battery charger, BUT thats 5A to each battery. Only 1 battery powers all the ACC. The other is just a starting battery.

After an hr or so of playing the stereo in the slip with the shorepower/charger on, the stereo/amps would shut down for lack of juice. Have even been watching a movie thru the headunit but with amps off, and the rope lights on and the DVD would quit playing do to low voltage. Even with the charger on. I'm thinking of going to a 30 amp charger: 20 amps to house battery, 10m amps to starting. battery. Just want to make sure it's big enough, hence the draw testing. I'm just not sure doing it right.

Yes, the probes were in either the 10A or lower AMP value plugs depending on range I was using.


Fuse is good. Checked it.
Thanks

In the Formula's there is a constant hot feed to the stereo for memory feed ....even with the batteries switched off its hot .. a pink wire ... 1 amp breaker .... Also the bilge pumps are hot all the time .....seems you could get more than an hour of what you described ...Have you tested the battey? I'm thinking about adding the third battery too for house load .. I know you hate the 2 batteries for starting doing nothing but if you were out somewhere you might be glad yo have them ...if you ad the third battery you'll need a charger with 3 outputs ..plus Like Chris states an Isolator ...cept I would use one that isolates all three batteries for charging while underway ...m

to get an accurate measurement disconnect the ground cable and go between the - cable and the battery with your meter
Phil

AUGH!

Truer words have never been spoken. :drink:

4 fuses later at $10 a pop, this trouble shooting chit is going to be costly. :D

I know that the 'A' is straight amp reading when the probe is plugged into the mA/A socket. Meaning 1 A, 3A, so on up to 10 A. I think....:rolleyes:

The milli and micro range terms are foreign words!

But when checking for something like the memory draw on the radio, it shows something like 0023. Is that .0023, .23, or 2.3 amps? Don't recall the exact reading as after the 2nd fuse popped, US1 wasn't a happy camper and was just looking for something to do anything to make numbers pop up. Tried different combos of probes/dial settings. Course the wrong ones ended up in blown fuses.

2 probe choices, A and mA/uA
2 dial choices: mA/A and uA

Which ones do I use? and what will the readings be as?



What I did see is an inconsistancy betweeen the 2 stereo amps. One had a lot lower number than the other (0039 vs 2250) while both off. (remote turn on signal wire switched off) So I assume this means 1 has is drawing current even while off. Just don't know what the actual numbers mean.


I see I can get AC/DC clamp meters that go up to 1000A. I assume these have no fuses to be blown? Do these have straight forward readings such as .5 or 5 amps?

There are two main current "Ranges" on most digital multimeters.

You have, amps, and milli/micro amps. Basically to combine both ranges would make for a terribly inaccurate measurement, so they separate them. You have to know ahead of time what measurement to expect before you try and measure.

If are unsure of what to expect, then start on the high range and work down. So, measure Amps (anything over 1A, or 1000mA). Put the probe on common, and A plug. If the measurement is close to zero, or .00 something, switch to the milliamp mode. Then, move the probe to the mA/uA plug, and measure in milliamps. Is it still zero, then switch the dial to microamps. Once you get a reading you will know your in the range with a good accurate number.

Now, all that you said is going to draw way more than 10 amps, so you can not measure it with a current meter. There are two ways to measure after that. A shunt, or a current transformer (ct/clamp meter). The clamp meter goes around the wire transmitting power, and through inductance has a proportional output. You then use the clamp meter, or a DVM hooked up the the CT to calculate current draw.

A shunt can be place in series with the main lead, and it has a resistance, which causes a voltage drop. The voltage at the max current the shunt is rated for is usually 50mV. So a 100amp shunt will output 50mv between the terminals for 100amp draw, 25mv for 50amp draw.

Thats how its done.

This is a really nice compact easy to use unit.


If you were closer I always carry a DVM and current clamp on me.

Thanks Joe.

I take it the different ranges work just like the metric system: 1000mm =100cm=1m and so forth?

yeah, kilo amperes, amperes, milliamperes, and microamperes.

A third deep cycle battery, with a good charger and isolator should solve the problem. We sell battery chargers, but not for marine enviroments.