>>>SIMPLE<<< 12V Battery Level Indicator

[absolutsnwbrdr]

Zach, Thanks for the post. I don't want to carry a voltage meter around and my battery is mounted underneath the trailer where it's hard to get to. This is the kind of solution I'm considering. Are you going to wire it so that it automatically shuts off power to your 12v accessories? The wiring below is from the Ebay listing.

Pin 1 is for Positive Volts DC

Pin 2 is for Ground

Pin 3 and 4 are the connections to make use of the relay function. Connect a positive voltage supply to pin 3. Connect pin 4 to equipment that you wish to operate limited to 3 amps max. This connection provides an open switch. When the meter senses full voltage, it activates the relay allowing current to flow to operate accessories. When the battery becomes discharged, the relay will open and shut off the power supply to an accessory that is wired thru the meter to conserve battery life.

I saw that too. That would certainly be helpful. I may wire it to shut off the power to my stereo system, but I would need to add a stronger external relay compared to what the meter has. The internal relay is only rated to 3A, and my stereo specs claim it pulls 3-5A. Using an external relay, you could even have it cut power to the entire trailer. I wonder what the shutoff voltage is though. If its in "the red" then thats kinda too late. If it shuts off at 20-30%, then that would be pretty good.

[absolutsnwbrdr]

Found an almost identical meter (it also has an hour meter) on Amazon, with this description:

The battery gauge, meter, monitor, charge indicator has an integral hour meter to monitor hours of operation. It is an accurate low battery indicator that provides a clear indication of the battery level of charge. It is water proof with a glass window. Only one LED lights at a time to save battery power. An internal relay output is also provided to power auxiliary equipment (max power output 90 watts). This relay will open and shut off the auxiliary equipment when the battery power is down to about 30% of full charge. The hour meter can be operated independently of the battery status indicator by connecting terminal 4 (may be marked C) to plus volts. Battery Gauge Indication The battery gauge or battery charge indicator has 10 LEDS that will light to show the battery level of charge. When fully charged, only the 10th LED will light shown as a green LED. As the battery discharges, successively lower LEDs will light; the 9th, 8th, 7th and so on lighting only 1 LED. At approximately 30% battery life, the #3 LED will light and the color is Yellow as a caution indicator. Relay will open shutting off power to auxiliary equipment if this function is used. At approximately 20% battery life remaining, the #2 LED will light as a Flashing Yellow. When the battery discharges to approximately ~10% remaining life, the #1 LED will start FLASHING RED with the #2 LED FLASHING Yellow alternately. It is recommended to have the battery or batteries recharged when the #3 LED lights Yellow as a safety margin to prevent dead batteries.

That one appears to have an internal relay capable of 7.5A (90W/12V).

[jonw]

Unfortunately I don't think any of these will work well with deep-cycle batteries, or at least will mis-read them. I suspect I'll need to go the Doc Watson route...

[absolutsnwbrdr]

Unfortunately I don't think any of these will work well with deep-cycle batteries, or at least will mis-read them.

Would you care to elaborate?? Why won't the Doc Wattson mis-read them? If I understand correctly, and I'm pretty sure I do, the only accurate way to measure battery usage and capacity is to measure the amount of energy going in AND out. IIRC, the Doc Wattson only reads one way. I think this is probably why SC spent the big bucks on the Victron.

[GuitarPhotog]

. Connect pin 4 to equipment that you wish to operate limited to 3 amps max. This connection provides an open switch. When the meter senses full voltage, it activates the relay allowing current to flow to operate accessories. When the battery becomes discharged, the relay will open and shut off the power supply to an accessory that is wired thru the meter to conserve battery life.

With contacts rated at only 3A, you may burn out your contacts with a normal load. My TD draws about 3.5A just running normal reading/cooking lighting.

That is a very light duty relay.

<Chas>

[parnold]

Unfortunately I don't think any of these will work well with deep-cycle batteries, or at least will mis-read them. I suspect I'll need to go the Doc Watson route...

Jonw: Are you old enough to remember cars that used floats for fuel level? The gauge that Zach has, and the Doc Wattson both are basically like a float. A pretty close approximation. Not they are not 100% accurate, but for the majority of us, they will provide the information we need. If my battery approaches 50%, and I'm not near power I will charge my battery from my tow vehicle with jumper cables. I might really be at 41% or 58%, but it really doesn't matter enough to me to spend close to $200.00 for a more accurate device. I'll gladly spend 30 though for a rough estimate.

OH.. I never ran out of gas with my 64 beetle either, even though the gas gauge was ridiculously innacurate.

[absolutsnwbrdr]

. Connect pin 4 to equipment that you wish to operate limited to 3 amps max. This connection provides an open switch. When the meter senses full voltage, it activates the relay allowing current to flow to operate accessories. When the battery becomes discharged, the relay will open and shut off the power supply to an accessory that is wired thru the meter to conserve battery life.

With contacts rated at only 3A, you may burn out your contacts with a normal load. My TD draws about 3.5A just running normal reading/cooking lighting.

That is a very light duty relay.

<Chas>

3.5A for lights? Go get some LED pods man!!

I agree though... that relay is very light duty.

[jonw]

Yeah, I am old enough to remember.

I believe deep cycle batteries can be safely discharged at voltages below regular lead acid batteries, and can be safely and repeatedly recharged from these lower levels.

My (possibly incorrect) thinking was that a meter calibrated for a lead acid battery would not read the percent of discharge correctly from a deep cycle battery, and would indicate it was more drained than it actually was. In other words, the state of charge diagram referenced above probably does not apply to deep cycle batteries - the voltages for each percentage would be different.

If you were using the meter wired to cut off power below a certain threshold, for a deep cycle battery you'd actually be doing so prematurely and would not be able to fully utilize all the power in the battery.

I know that a higher voltage should be used to charge a deep cycle battery but I don't know if that would affect these meters or not.

If I'm blowing smoke here someone with more knowledge about these things please jump in...

Thanks.

[jonw]

Unfortunately I don't think any of these will work well with deep-cycle batteries, or at least will mis-read them.

Would you care to elaborate?? Why won't the Doc Wattson mis-read them? If I understand correctly, and I'm pretty sure I do, the only accurate way to measure battery usage and capacity is to measure the amount of energy going in AND out. IIRC, the Doc Wattson only reads one way. I think this is probably why SC spent the big bucks on the Victron.

Zach - the Doc Watson reads out actual voltage and amp (and other) values, and doesn't extrapolate them to a percentage. That's all I'm sayin...

[absolutsnwbrdr]

Unfortunately I don't think any of these will work well with deep-cycle batteries, or at least will mis-read them.

Would you care to elaborate?? Why won't the Doc Wattson mis-read them? If I understand correctly, and I'm pretty sure I do, the only accurate way to measure battery usage and capacity is to measure the amount of energy going in AND out. IIRC, the Doc Wattson only reads one way. I think this is probably why SC spent the big bucks on the Victron.

Zach - the Doc Watson reads out actual voltage and amp (and other) values, and doesn't extrapolate them to a percentage. That's all I'm sayin...

No problem I was just curious. The product description for this little meter does say its for golf carts and forklifts, and I believe that they are a type of deep cycle battery. I could be wrong.

I do agree that a digital readout would be more precise. But precision and accuracy are two different animals. Basically, I'm not concerned whether my battery is at 12.23V or 11.91V. As long as I stop using it before I hit red, I'll feel that I'll be fine. Then as soon as I have access to electricity, I'll plug her in and let the battery charger/maintainer bring it back up to "full charge".

[droid_ca]

would this work if you were running more then one battery? or would the increased Amps burn it out?

[absolutsnwbrdr]

would this work if you were running more then one battery? or would the increased Amps burn it out?

Since this only measures voltage, I'd say that it would be fine. Voltage is measured in parallel, whereas current is measured in series. The current limitation of 3A is only for the internal relay (if you choose to utilize it)


*I'm no electrical engineer, but I do have a couple degrees in electronics technology and fiber optics/microwave communication systems, so no I'm not ignorant to electrical theory

[jonw]

Ok, here is some info from my Optima Yellow-top (deep cycle) D25/75 model battery:

Open Circuit Voltage (Fully charged): 13.1 volts
Battery Charger (Constant Voltage): 13.8 to 15.0 volts
Float Charge: 13.2 to 13.8 volts

It mentions 100% discharge is 10.5 volts which does line up with the state of charge diagram. So I stand corrected on the low end, but the higher voltage at 100% will still cause somewhat incorrect readings. But I do agree with Paul, it's close enough for gov't. work... I think we're all in violent agreement!

[absolutsnwbrdr]

it's close enough for gov't. work...

PERFECT!!

[parnold]

it's close enough for gov't. work...

Unfortunately if this was for the gov't, it would be a $500.00 gadget, not a $30.00 gadget.