# How About a Boost?



## RJSakowski (Jan 25, 2022)

I have two deep cycle batteries on my fishing boat; one fore for the bow mount trolling motor and one aft for the transom mounted trolling motor, the sonar/GPS, and miscellaneous electronics. The aft battery also is used for starting the outboard. The aft battery has a few years on it and has been losing capacity although I'm not quite ready to chuck it yet.

The dilemma is this; if I use the rear trolling motor too much, I stand the danger of depleting the battery to the point that it won't start the outboard. While it is possible to pull start the motor, the cowling has to be removed and a length of rope used. Add to that, that it is a 50 hp. motor and takes a bit of oomph to pull start it.

A solution I tried was to purchase a booster which had rechargeable Li-ion batteries and can put just enough charge into the battery to start the motor. The problem with that was that the batteries don't do well when stored in a hot compartment on a boat. The first time that I needed it, it was totally dead.

However, it came to me last fall that I had another battery up front that I could use. I went on line and bought a DC-DC converter which would operate on a supply voltage between 8 volts and 16 volts and output a user set constant voltage between 12 volts and 60 volts and a user set constant current between 0 and 10 amps.








						600W DC-DC Step Up Boost Buck Voltage Converter High Power Supply Module 16A   | eBay
					

(Input 36V 10A=360W, input 48V 10A=480W, input 60V 10A=600W. Module nature: non-isolated boost module (BOOST) (can't step down). Output current: 12A MAX. More, the lower the charging current.). The circuit structure of the boost module cannot be adjusted in a short-circuit mode.



					www.ebay.com
				




The idea was to provide a connecting cable between the two batteries and use one battery to boost the other. My boat has two sets of exposed charging posts so a 15' connecting cable and battery clips would complete the booster. Even a dead battery would generally have enough charge left to provide 10 minutes of charge at 10 amps which would be enough to start the outboard.

I bought a 15 ft. 16 AWG zip cord at the DIY for the input side and pulled a 3 ft length of zip cord from my collection for the output side. Two pairs of battery clips provided the connections. While it would have worked as is, I decided to add a digital volt/ammeter for monitoring the charge current and the output voltage.








						Mini DC 100V 10A Digital Voltmeter Ammeter Blue Red LED Volt Amp Meter Gauge US  | eBay
					

Current Testing range: DC 0 - 10A. - Display: 0.28" digital tube, Two color blue and red. You will be pleasantly surprised by our service. - Got a problem?. No Problem. This can only delay our service.



					www.ebay.com
				




The only actual machining was making a protective case for the electronics. I used a piece of .063" aluminum for the case cut into a cross configuration. Since I had eight blind cuts to make as well as a cutout for the meter, I decided to use the mill. I had eight inside corners which I filed square.

One of the case dimensions was 3" which was fortuitous was I could use a 1-2-3 block as a bending form. The other dimension was close enough to 2-3/8" that a 3/8" x 3/4" bar between the 1-2-3 blocks could be used for support. To make the bends, I clamped the blank to my RT using the two 1-2-3 blocks and strap clamps. A wood chisel allowed me enough purchase to start the bends and a piece of flat stock was used to bend the side close to 90º. A little bit of hammer work and I had nice crisp bends. The same was done to bend the 2-3/8" sides. With the box bent up, I used Miracle Rod aluminum braze to join the sides. After checking the fit of the meter bezel and the box to the DC-DC converter, I gave it a quick coat of flat black enamel.

The converter has two modes of operation, one which has an input voltage range of 8-16 volts and a second where the input voltage can range between 12 and 60 volts, selectable by jumper. I chose the former setting. A constant voltage/constant current supply functions so that neither of the settings will be exceeded. As a charge approaches completion, the charge current will be limited by the set maximum voltage and will drop to a lower value. I set the output voltage at 15 volts which is a safe short term charge voltage for a lead acid battery regardless of state of charge. I set the charge current at 10 amps.

Piece of mind....priceless!


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## Aukai (Jan 25, 2022)

My boat had 2 engines, and 2 banks of batteries, if I killed one side running electronics, and lights at night this switch was between the 2 banks. 1 positive to #1, and one positive from the other bank to #2, and left the switch in the off position unless needed.


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## mksj (Jan 25, 2022)

Lithium Iron Phosphate (LiFePO4) Battery have very low rates of discharge even at temperatures up to 50C, not inexpensive, but compact and light compare to traditional batteries. Was considering one for my car, but a bit too pricey vs. the 5-6 years I get out of a standard lead acid. Also seems to be used for solar energy banking.


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## Dhal22 (Jan 26, 2022)

I use LiFe batteries in my large radio control airplanes.   Virtually zero discharge right now while I wait for spring.


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## jeffkash (Jan 26, 2022)

Dhal22 said:


> I use LiFe batteries in my large radio control airplanes.   Virtually zero discharge right now while I wait for spring.


Where do you fly?


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## Dhal22 (Jan 26, 2022)

NGMA 

Ngmarc.com

You?


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## jeffkash (Jan 27, 2022)

Dhal22 said:


> NGMA
> 
> Ngmarc.com
> 
> You?


Cobb County Radio Control Club


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## Alcap (Jan 27, 2022)

I’m trying to grasp what you did . Your taking a slightly discharged trolling motor battery and stepping up the voltage above say 14volts at  10 amps to charge the outboard motors battery ?


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## Dhal22 (Jan 27, 2022)

jeffkash said:


> Cobb County Radio Control Club




What do you fly?  I love glow classic pattern but generally fly gas (currently 107" Yak and 3.1m Sukhoi).


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## extropic (Jan 28, 2022)

RJ,

Please explain why you didn't just use jumper cables?

Are both batteries normally charged only from shore power (no alternator on the motor)?


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## RJSakowski (Jan 28, 2022)

Alcap said:


> I’m trying to grasp what you did . Your taking a slightly discharged trolling motor battery and stepping up the voltage above say 14volts at  10 amps to charge the outboard motors battery ?


The booster steps up the voltage to 15 volts to provide 10 amps of charge current.  Ten minutes of charging will provide enough charge on the dead battetry to start the motor.  The booster will provide 15 volts , 10 amps with an input as low as 8 volts.  In theory, I could use a dead battery to charge a dead battery, squeezing the last few electrons out. (A dead battery would be one at 11 volts or less).  I seldom completely discharge either battery.


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## Alcap (Jan 28, 2022)

That’s kind of what I thought you were doing !   Fantastic!     Have you tried it out yet ?


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## rwm (Jan 28, 2022)

This is brilliant! 
Robert


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## RJSakowski (Jan 28, 2022)

Alcap said:


> That’s kind of what I thought you were doing !   Fantastic!     Have you tried it out yet ?


Both my batteries are fully charged so not on the boat.  I have fed it into a .8 ohm load though and it was putting out 10 amps with less than 11 volts on the supply battery.


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## rwm (Jan 28, 2022)

Ya know. If these are not in production, I think you could sell these. Many boats have 2 batteries and it is not unheard of for some idiot to run them both down too low to start the 496. All you have to do is leave the switch in the ALL position, turn up the radio and open the cooler. Or some variation of that....


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## extropic (Jan 28, 2022)

@RJSakowski 

The link you posted for the "boost buck" sold at $17.99, but the sellers "re-listing" is $117.99.  Crazyflation.

A search shows it elsewhere for $23.49.









						600W DC-DC Step Up Boost Buck Voltage Converter Power Supply Module 16A  | eBay
					

Input Current: 16A (MAX). - Enhance heat dissipation over 10A operation. - Output Current: 12A MAX ,over 10A enhance heat dissipation. - Properties: non-isolated step-up module (BOOST). - Do not exceed the maximum arc distance electricity.



					www.ebay.com
				




Thanks for the thread and the detailed explanation.


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## Flyinfool (Jan 28, 2022)

So, just thinking out loud, if your dead charge battery is at 8V and you are putting out 15V at 10 A to charge the starting battery. that means that the dead supply battery has to be able to hold that 8V while outputting ~20A.


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## rwm (Jan 29, 2022)

Flyinfool said:


> So, just thinking out loud, if your dead charge battery is at 8V and you are putting out 15V at 10 A to charge the starting battery. that means that the dead supply battery has to be able to hold that 8V while outputting ~20A.


This is true. Energy must be conserved. I am thinking that a lot of times, the battery is just dead enough not to crank the engine and just needs a little help.


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