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Can Digital Ammeters Display Both Negative and Positive Current?

12/02/2017 1:25 PM

Hello All. Can anyone provide some advice on the following please?
I am trying to work out whether modern digital ammeters are capable of being wired up to display DC current as both the normal positive way (i.e. the load on a system), and also in a negative way. The old car ammeters (not digital) were capable of displaying the current being used by a car (or in my case a boat), and once the engine's alternator was working it would display the current going back into the batteries (presumably minus the load current). I assume that this latter display would have been the difference between the alternator's nominal charging current (e.g. 60 amps) less the load being consumed by the car/boat at the time (e.g. 15 amps with lights/heater etc etc), so would display 45 amps.
My thinking is that such a display would confirm that overall the alternator is successfully charging the boat batteries at a net rate of +45 amps whilst the boat's engine is working and once the engine is stopped (e.g. to do some fishing), then the current display would then display -15 amps (i.e. the system load).
Can anyone please advise whether such an arrangement is possible with the cheap modern digital ammeters (e.g. those available from eBay links below)?
My ideal arrangement would be a dual 12V DC digital voltmeter combined with a 12V 50A digital ammeter.
I've seen some round shaped digital voltmeters which also have set of red/amber/green LED's around the perimeter of the display see

https://www.ebay.co.uk/itm/Car-Digital-LED-Volt-Gauge-Meter-Voltage-LED-Panel-Voltmeter-Display-DC-12V-New/302484123665?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D2%26asc%3D49480%26meid%3D6f1a0a0eb6a44de19b88b5f6cb6dc9bc%26pid%3D100005%26rk%3D3%26rkt%3D6%26sd%3D152563575373&_trksid=p2047675.c100005.m2219

The various coloured LED's light up according the the actual voltage e.g. 12V+ displays all the red & amber LED's plus some of the green ones. This coloured LED arrangement enables the user to very quickly see if there is a voltage issue whilst fishing e.g. if suddenly all the green LED's extinguish.
The combined voltmeter/ammeter below is a reasonable compromise but isn't ideal as it doesn't have the extra perimeter coloured warning LED's

https://www.ebay.co.uk/itm/DC-10-20A-12-24V-Dual-LED-Digital-Voltmeter-Ammeter-Amp-Volt-Meter-Guage-/142122673209?_trksid=p2349526.m2548.l4275

Does anyone know if there is my ideal combined 12V 50A digital volmeter/ammeter with additional warning coloured LED's out there which can display both negative amnd possitive current being consumed?
Thanks for any help in advance!

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#1

Re: can digital ammeters display both negative and positive current?

12/02/2017 2:03 PM

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

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#2
In reply to #1

Re: can digital ammeters display both negative and positive current?

12/02/2017 2:40 PM

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

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#6
In reply to #2

Re: can digital ammeters display both negative and positive current?

12/02/2017 3:56 PM

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)

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#8
In reply to #6

Re: can digital ammeters display both negative and positive current?

12/03/2017 8:42 AM

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

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#11
In reply to #8

Re: can digital ammeters display both negative and positive current?

12/03/2017 10:39 AM

You're welcome. Keep your lines tight!

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#3

Re: can digital ammeters display both negative and positive current?

12/02/2017 3:17 PM

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.

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#4

Re: can digital ammeters display both negative and positive current?

12/02/2017 3:26 PM

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

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#7
In reply to #4

Re: can digital ammeters display both negative and positive current?

12/02/2017 4:46 PM
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#9
In reply to #4

Re: can digital ammeters display both negative and positive current?

12/03/2017 8:46 AM

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

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#12
In reply to #9

Re: can digital ammeters display both negative and positive current?

12/03/2017 10:58 AM

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

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#15
In reply to #12

Re: can digital ammeters display both negative and positive current?

12/03/2017 12:26 PM

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.

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#18
In reply to #15

Re: can digital ammeters display both negative and positive current?

12/03/2017 4:37 PM

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

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#20
In reply to #9

Re: can digital ammeters display both negative and positive current?

12/04/2017 4:22 PM

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

Wow! REally?

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#5

Re: can digital ammeters display both negative and positive current?

12/02/2017 3:27 PM

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

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#10

Re: can digital ammeters display both negative and positive current?

12/03/2017 10:09 AM

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.

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#13
In reply to #10

Re: can digital ammeters display both negative and positive current?

12/03/2017 12:03 PM

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

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#16
In reply to #13

Re: can digital ammeters display both negative and positive current?

12/03/2017 12:31 PM

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

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#17
In reply to #16

Re: can digital ammeters display both negative and positive current?

12/03/2017 12:42 PM

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.

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#14
In reply to #10

Re: can digital ammeters display both negative and positive current?

12/03/2017 12:21 PM

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.

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#19

Re: Can Digital Ammeters Display Both Negative and Positive Current?

12/04/2017 4:21 PM

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

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Users who posted comments:

Dennis R. Levesque (2); James Stewart (2); Kilowatt0 (1); lyn (3); redfred (1); Rixter (1); SolarEagle (4); SteveAinsworth (6)

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