Help from the electrical people please

[CRS]

I have a Tracker Grizzly 1448 on the front I have a Minn Kota Ulterra 80 pound thrust on the back I have two Traxxis 80 pound thrust. Minn Kota refuses to give any estimate on how long the run time is for their motors. I know that wind weight and current will change the distance and speed achieved but it should not effect the actual run time. They give the amp usage at top speed but none for the lower speeds. The battery meters built in are like a poorly designed gas tank that will read full until it's about out of gas. I have run the two transom motors for 2 hours at 50% and still the meter shows full charge. The Ulterra read full charge for about 2 hours hard running ( I was not timing it) until it dropped to 75% then rapidly dropped to 50% then 25% in less then 30 minutes. (I had to paddle the last 200 yards) Each motor is hooked up to 120 amp hour AGM batteries. My question: How can I accurately measure the amount of discharge and calculate the remaining run time.
Information: the 2 Traxxis 80 pound thrust at max gives me 4.7MPH (speed given on the Ulterra hand device and agreeing with the Humming bird fish finder.) I like the 3 motors because I do not like rowing or paddling since the Grizzly is not designed to be rowed or paddled. If a motor fails when i am 3 or 4 miles from the ramp having the multiple motors is necessity.

 

[DaleH]

Never saw them applied to trolling motors but many of us who fish waaaaaaaay offshore added 'amp hour draw' battery monitors, as they function as a real time indicator of amp draw and remaining amp hour battery status.

I'd give them a call and see what they can advise you, for use with trolling motors: https://www.xantrex.com/power-products/power-accessories/linkpro-battery-monitor.aspx

I'm not sure you have enough total battery capacity. You are aware, aren't you, that for maximum battery life that you should never discharge more than half the rated capacity of the battery?

 

[Scott F]

Brand new batteries may have 120 amp hour ratings, but depending on their age and how well they’ve been maintained, that number may drop. Also, the rate of discharge on the batteries, as you’ve seen is not linear. As a battery is used up, the voltage drops. As the voltage drops, the amperage draw increases so the battery will drain faster than it did when the batteries were fully charged. How many total batteries are you using now? Your best bet is to purchase a digital volt meter for each set of batteries. Also, if you are running out of juice, you may need to connect more batteries. An Amp meter showing what the actual amp draw is at any time might give you more information as to what is going on on your boat. One last thing, what kind of battery charger are you using? Does it fully charge all your batteries? Are all the batteries the same age and condition?

 

[CRS]

the ulterra has batteries 1 season old the traxxis motors each have new batteries. each motor has its own 2 battery system. I know that batteries should not be discharged more then 50% that is why my questions. I am attempting to establish the amount of time I can run the motors at certain speeds without going past the 50% discharge. As I stated the meter on the motors are useless and very inaccurate. Using an amp meter is a thought I had to find the 50% line. Problem is I do not know what I am reading to translate the numbers into the value for the remaining charge. I will check on the gauges mentioned.