Can Digital Ammeters Display Both Negative and Positive Current?

Vexilar D-130 Digital Battery Status Indicator $24.99 Sportsman's Gu... Special offer

Thanks for your reply, Lyn.

Unfortunately though that device doesn't measure (or display) the current (in Amps) at a point in time, just the overall battery condition i.e. its percentage charge.

I really want to be able to see the effect in terms of both battery voltage and current when various devices on the boat are switched on or off. Some devices e.g. a 1100 gallon per hour livewell/bilge pump, draws some 1-6 amps depending on a variable (rheostat) speed setting, so I would like to be able to monitor the overall current being drained from the boat's batteries whilst the engine is switched off (and not being charged by the alternator).

Sometimes, for example, when fishing at anchor for several hours, the engine will be off and the boat's batteries will be drained fairly quickly, leaving the possibility of insufficient charge to start the engine later! Not an ideal situation with a large inboard diesel engine that cannot be hand started!

I also need a fairly quick visual "alarm" ideally such as the red/orange/green multiple LED's which surround one of the example meters I listed.

The reason for that is when I am busy fishing I will be concentrating on the fishing and just want an obvious instant coloured display when I return to the boat's console. I believe the first example would achieve this requirement but unfortunately it lacks the current measuring display.

Some other devices combine both digital voltage and current but they do not have those multi-coloured warning LED's.

Thank you for your reply anyway.

Regards

What's more important to you? A visual indication of the state of charge of the battery/batteries on your boat or how much power is being drawn from them?

Knowing the amp drain on your batteries is worthless information unless you can rapidly calculate the level of charge of your batteries based on varying power drains with bilge pump on/off etc. I don't believe such a gauge exists.

So, get two instruments. The round volt meter, as you already found and an amp meter. (probably an analog)

Hi again Lyn and thanks for your reply.

If I had to choose between voltage/battery "state" or current, I would choose voltage over current, but I'm really looking for both so I can monitor how much current drain each device (fishfinder, livewell pump(s), lights, fan, radios etc etc) contributes to the total current drawn, especially while the engine is off and the alternator is not charging.

I was hoping to find my "ideal" setup in a single instrument rather than two. With my limited knowledge and after fairly extensive "Googling" I wasn't able to find the perfect single instrument so therefore sought advice from this community in the hope that someone would be aware of such an instrument at a very reasonable price i.e. less than £30/$40.

It looks like I will have to lower my expectations and install 2 separate instruments as you've suggested.

The device that SolarEagle mentions below, is unfortunately too expensive ($343) even though it may well have the functionality required. I like the look and description of the digital voltmeter surrounded by multiple (3 coloured) warning LED's that I originally mentioned, as I believe this will give a rapid assessment (at a glance) of the overall battery state/voltage without having to necessarily even read the voltage reading whilst I am busy fishing etc. The other instrument would be a digital ammeter hopefully installed so that I can see both positive and negative current to reflect the alternator working (or not with the engine off).

Thank you for your advice.

Regards

You're welcome. Keep your lines tight!

Yes, one can acquire a digital or analog current meter that measures and displays both positive and negative directions of current. One can also acquire an ammeter in either analog or digital format that can only display one current direction.

Something like this?

DC Digital Multi-Function Meter with Alarm

8248

• Displays amperage from -500 to +500 Amps
• Displays voltage from 0 to 60 Volts in 0.01 Volt increments
• High and low voltage, audio and visual alarms
• Standard meter operates in negative side of circuit only. Shunt Shifter required for positive side installation such as alternators
• 3 levels of display brightness
• Programmable sleep mode blanks display for power conservation
• Splashproof front
• Includes 500 Amp shunt

https://www.bluesea.com/products/8248/DC_Digital_Multi-Function_Meter_with_Alarm

DC Shunt Shifter

8242

• Shunt Adapter for DC Digital Ammeter positive side shunt applications, such as alternator measurement
• The Shunt Shifter is designed for use with Blue Sea Systems’ 8255 Digital Meter Shunt
• Advanced technology shifts the shunt’s positive reference to negative as required by digital meters
• Easily installs directly onto shunt using existing sense screws
• Ideal for use with 12-36 Volt DC systems
• Includes all necessary hardware

https://www.bluesea.com/products/8242/DC_Shunt_Shifter

https://www.amazon.com/Blue-8255-Digital-Meter-Shunt/dp/B00TLFAL6I

Thank you for your reply but unfortunately this product would be too expensive for me, but thanks anyway.

Regards

So what's your budget? You can buy used...

Thanks SolarEagle.

As little as possible! I've seen several compromise options (i.e. devices that don't do everything I want) for under £20/$30. I wouldn't need to justify that sort of expense level to "she that must be obeyed" (the wife)!

Thanks again.

Regards

Ah yes the alternative for me in that sort of situation is bartering around the old boatyard....Bartering for goods and services is categorized as just helping friends out in the court of marital inquiry.....haha

Even a cheap one at Sutherlands or Home Depot will show forward or reverse current.

Wow! REally?

You can clamp one of these around your battery cable when you go fishing and put it in your toolbox at home.

Here is on for ~$18 for a 100A $24 for 400A meter from Amazon. Hall effect ammeter and volt meter combined. If the current is negative, it puts a small dot in the lower right corner.

For only a dollar more, you can get this one by the same company. It includes a power (0-10KW) and energy reading (0-9999KWh), too. But the voltage limit is only 6.5V-100V. https://www.amazon.com/bayite-6-5-100V-Display-Multimeter-Voltmeter/dp/B013PKYILS/ref=pd_bxgy_328_2?_encoding=UTF8&psc=1&refRID=W3QP6D9ZBXN033HEKVFC

Thanks Dennis R. Levesque.

I've seen very similar ones on eBay and I am compiling a short list of the options currently (that will be on it). The only thing that put me off this type initially was the fact that it's an LCD screen as opposed to LED screen so not quite so easy to see with a quick look like the LED's but if it does everything else I want then I could go for it.

Thanks again.

Regards

Another thing to consider: This is not for use outdoors. You might need to get one more rugged for boat use, or weather-proof this one.

Thank you Kilowatt0.

I haven't seen one of this type yet so it looks interesting especially as it appears that I could install the hall effect sensor around one of the main high current battery supply cables and presumably in that way it could possibly even display the DC current being used by the starter motor (unless of course that exceeds 100A which it may well do). In addition it should display both the net charging current (alternator current minus the load current) when the alternator is working, and just the load current when it's not working.

Thanks for that.

Regards

Yeah they can, just hook them up backwards, and get a negative number.

Yes, most digital meters will display Negative and Positive.

To make a digital ammeter all you need is a millivolt meter (cheap multimeter for example) and a suitable current shunt. A shunt can also be just part of the existing wiring tapped into at the correct spacing to give you 1 millivolt per Amp

2.9 inches for #16, 4.5 inches for #14, 7.7 inches for #12 etc

Just bare off a little insulation and solder a couple of small wires to the conductor. It's very important that there are no joints in the wiring and the current connection must not be made at the Voltage tapping point or the reading will be effected by joint resistance.

Try it out by touching your meter probes to the copper.

If you have wire of an unknown size it's dead easy to calculate the tap spacing, just pass a known current through it, tap in at a couple of spots a few feet apart then back calculate the correct spacing. Of course if you want 1 decimal place just make the tap points 10 x greater.

I measure the starter current ~170 Amps with a #12 shunt, it's ok for 10 seconds or so.

Roy