Low Cost Battery Monitor

[chala]

Originally Posted by sparrowhawk1

If anyone knows of one for under $100 please let me know

This may help.

Originally Posted by chala

Note:
Q2220 from Dick Smith
QP-5570 from Jaycar
Shunts QP-5412 & QP-5414 from Jaycar

[sparrowhawk1]

Thanks to Vladis I may be able to fine tune my meter. My meter is a little different than his, disconnecting it from the power supply didn't seem to make a difference. the middle button marked "out" is held in to go to settings. Then pressed to go to different settings.the buttons above and below are for increasing or decreasing. The first setting is for voltage the second setting is for current and the third setting which he PM'd me about on my meter says 2-Fl. On the top and has a number on the bottom. I can't change the 2 - FL but the number on the bottom can go from zero to in the hundreds. And by changing that I've been able to make my amperage readings much more accurate. The multimeter I'm using to calibrate only goes up to 10 amps so the best I can do is turn on a bunch of lights till it gets close to 10 amps, turn everything off to read close to zero amps. And keep messing with the number on the bottom of the 2- FL "screen"

[sparrowhawk1]

Up date. My meter reads accurately from zero to eight amps. And I'm assuming that it's accurate to a much higher amperage but I'm limited in my testing to my multimeter. Thanks again Vladis

[sparrowhawk1]

Just realized I can check the accuracy at high amps by turning on a high amperage item and turning on and off a light of a known amperage draw. At 4a it goes to 6. At 70 it goes to 72. spot on. And now I know how much amperage my induction stove uses

[powerelectronic]

I'm entertaining thoughts of mounting the display in my cockpit behind a clear plexiglass waterspray barrier. Can anyone tell me if the LEDs are sunlight readable?

[antoha]

Vladis, is this an autopilot course computer in the battery compartment i see in your first photo? does it mind being so close to batteries in particular and strong currents in general?

thank you!
Anton

[Vladis]

Originally Posted by sparrowhawk1

Just realized I can check the accuracy at high amps by turning on a high amperage item and turning on and off a light of a known amperage draw. At 4a it goes to 6. At 70 it goes to 72. spot on. And now I know how much amperage my induction stove uses

Hello,

A friend of mine pointed me out a way to calibrate the monitor for high currents with a cheap multimeter like ours. You need to make a voltage divider with precision resistors. In the following drawings I have my system shown in one of the drawings and a modification for the setup in the other.

My shunt is 100A 75mV. Therefore it is a resistance of 0,75 mOhms. Using the shown resistors I have a voltage divider of 1:223. If I measure a voltage of 12,5V across the battery, the 100 Ohms resistor has a voltage drop of 56mV. This voltage is supplied to the monitor. If it was 75mV the monitor should display 100A. With a voltage of 56mV, the monitor should show 74,66A. I hope this is useful to check the precision of the system.

Anthoa - yes it is. It came from Beneteau as shown. The only problem I had with the autopilot was when I placed a box with loudspeakers near the autopilot compass which is located in the wardrobe!

Powerelectronic - The LEDs are normal 8-segment units. They are bright but I did not test them on sun light.

Regards, Vladis

[antoha]

Vladis, thank you. About to install an autopilot on our boat, trying to figure out the safe distance to dc currents (e.g. batteries), fluctuating currents (e.g. speakers and radios), and metal (e.g. engine). Very tight, and i also don't want to run miles of wires (ohmic losses).

[Jim Cate]

FWIW:

After reading the early posts in this thread, I ordered one of these units. Arrived on sched, was well packaged, the instructions were clear and in good English, the wiring diagrams were also clear, and the supplied parts were in good nick and seemed of reasonable quality.

How nice!

Got it installed yesterday, found the voltage calibration to be ~0.1 volt off, easily corrected. The Ammeter agreed with my old one very closely at both high and low readings... except: at low currents there is a lot of jitter in the displayed values. Not sure it this is solely an artifact of the high sample rate (5/second) or if there is noise on the low voltage lead from the shunt. This lead is twisted pair with a shield, but I haven't yet messed with grounding the shield.

I have not bothered with the monitor functions (Amp hours in/out, batt level) because I don't think they can be usefully accurate without means of altering the Peuk... (I can;t spell that name) coefficient.

All in all it seems a good value indeed. I really only needed to replace my old digital voltmeter which had died, but this unit was less expensive than a simple panel meter of decent performance.

Thanks to the OP for bringing it to my attention!

Jim

[sparrowhawk1]

This meter measures either amperage in or amperage out not both so amp hour function is only helpful to me at night when by wind generators aren't producing electricity. I might get another one in the future have one set for in and one set for out.

[rognvald]

If we take for a given that knowing your battery bank's voltage is more important than amp hours consumed(since this has the potential to be erroneous), why is a battery monitor needed when a multimeter can give you those figures?

[sparrowhawk1]

Originally Posted by rognvald

If we take for a given that knowing your battery bank's voltage is more important than amp hours consumed(since this has the potential to be erroneous), why is a battery monitor needed when a multimeter can give you those figures?

Voltage can only tell you state of charge if the battery has rested( no power in or out for several hours) that never happens on my boat

[conachair]

Originally Posted by rognvald

If we take for a given that knowing your battery bank's voltage is more important than amp hours consumed(since this has the potential to be erroneous), why is a battery monitor needed when a multimeter can give you those figures?

Take it for a given that it's all really useful even just a volt meter straight to the terminals is a fantastic real-time window into your batteries.
Record of amps out even better.
A multimeter doesn't come close as it isn't there a glance away.

[onestepcsy37]

Originally Posted by rognvald

If we take for a given that knowing your battery bank's voltage is more important than amp hours consumed(since this has the potential to be erroneous), why is a battery monitor needed when a multimeter can give you those figures?

Been doing that for ten years and very satisfied with the results, although I did eventually replace the multimeter with a $10 digital voltmeter. Last set of golf carts lasted six years (trojans) current set now going on four years (sams club johnson control).

Some people just overthink/overspend these problems...

[GrowleyMonster]

Originally Posted by sparrowhawk1

Voltage can only tell you state of charge if the battery has rested( no power in or out for several hours) that never happens on my boat

Actually, for a given load at steady state for a couple of hours, you can by experimentation arrive at a meter correction figure that will generally closely approximate the resting open circuit voltage. Lately, I have been doing endurance runs at different power levels with my 48v electric drive to find these corrections for my installation, and also to calculate my 50% SOC range at different speeds. Additionally, after only an hour at rest, the voltage will be fairly close unless the current drawn was a very large percentage of capacity. Sure, 6 hours is the rule, but you can fudge it a bit and be in the ballpark, so a voltage reading can be very useful if you have been carefully monitoring the batts and recording your data.