Battery Gauge with remaining time indicator

[zpalffy]

I saw a few threads on this but some of the links were very old and did not work so I am re-posting.

I would like to hook up a battery indicator to my trolling battery to show me how much time I have left on my trolling motor battery.
I know I need to check the status of the battery with the trolling motor off.
I know I should use an in-line fuse and I am thinking that I need 10 Gauge wire to run from my battery to my dash to mount my indicator and that the in-line fuse should be within 1 foot of the positive terminal.
I know that I should also install an on/off switch between the battery and the indicator as not to have the indicator also drain battery
I have read the the needle ones end up sticking
I have seen the status indicators ones where the status goes from green to red but I have no idea what that means in terms of remaining battery run time
I have also heard that some do not work when it gets too hot out and the sun beats down on the indicator all day and heats it up I saw some operating ranges up to 187 degrees.

all that being said of what I know and a whole lot more of what I don't know
does any one know of a good battery indicator ?
thanks

 

[Silvertip]

None of them can tell you remaining run time. They tell you percent of charge. These are basically a volt meter that is set up to indicate state of charge. Batteries are tested under load for a meaningful check.

 

[alldodge]

Agree ^^ if you install a voltmeter just use it and compare to this chart for lead acid bats

 

[fishrdan]

You can get a pretty decent panel mount 1"x3" LED volt meter off Ebay for $2 from China, takes a couple weeks to arrive. Reference (remember) the chart AD posted and you're good to go. Myself, it the batt is at 12V, it's discharged and done, so going from 12.7+-V down to 12V gives the range. It's one heck of a lot more accurate than the 4 (or 5?) light battery indicator that several of my TM's have built-in.

Also, you don't need 10ga wire to connect the meter as it draws very little current, 18ga and a 1 amp fuse would be more than enough. Wire for the TM itself is a different story as the wire gauge needed depends on the distance and current draw, 8ga is pretty common, but may need to go bigger depending on length of wire run. I'm using 6ga for a long run.

 

[gm280]

There are ways to do what you are looking for. But not easily. A circuit using a microcontroller or even a good PIC controller and a program would be needed. And they are available for other battery electronics. My laptop actually does calculate the remaining time on the battery if used at the same current draw or rate. So search the net for a circuit that can tell you what time remains on the battery.

But also understand that the time displayed will only be close to accurate if the current remains constant to the end. Any change in that current draw will certainly have to be recalculated for the new remaining time.

An easier and actually better idea is what AllDodge displayed in his reply. After a few outings, you will get the hang of percentage remaining to time. It is a learning curve but easy to figure it out after some real usages. JMHO!

 

[zpalffy]

thanks guys some really good info here that I can use the chart is not helpful. I agree that an actual reading is far better than and 4 or 5 light indicator, I will try the 1"x3" Led volt meter with a 8ga wire and a 1 amp in line fuse that should do it.

follow up questions

fishdan if I run the wire from the rear of the boat to the dash will 8 ga still be ok ?

AllDodge I see at the bottom of your chart you mention temperatures below 30 degrees Celsius (Below Freezing) can reduce a batteries capacity by 30%. Do you mean 0 degrees Celsius because thats freezing for Celsius. 30 degrees Celsius would actually be 86 degrees Fahrenheit. So what you are saying is that at a battery stored at the freezing point will reduce a batteries capacity by 30%. I am storing my boat in side but in a non heated storage unit. I live in northern Virginia I do not know how cold it can get in those storage units. So I guess the best thing would be to pull out both batteries and put them in my garage (also unheated) at home and charge them from time to time in during the winter months ? Or do I use a trickle charge on them ?

 

[alldodge]

Below 0 Celsius, so -30 C = -22 F
I leave the batteries in the boat with Bat switches in the OFF position and charger turned ON. If you don't have 3-stage charger or maintenance charger I would suggest pulling the Bat and charge them once a month or so for an or so (2 to 3 amps)

 

[Silvertip]

You do NOT use 8 gauge wire for the voltmeter. 18 gauge is adequate. Depending on the size of the trolling motor you need #8 or perhaps #10 for it. A switch on the instrument panel for a digital voltmeter is not really necessary. I have one of the Chinese cheapies in my cargo trailer and it is powered constantly. They use very little current.

 

[sam am I]

There are ways to do what you are looking for. But not easily. A circuit using a microcontroller or even a good PIC controller and a program would be needed.

#include <math.h>