Rethinking Battery Management

A

ATPNW

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Jul 26, 2020
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C Dory Year
2006
C Dory Model
23 Venture
Vessel Name
Fellowship
Current Setup

  • Twin Honda BF60’s
  • Two Group 24 Dual Purpose Batteries
  • Each motor has its own battery
  • All accessories are spread between the two batteries


Use Case

  • 90% of the time I am trolling for salmon, alternating every hour or so between each engine to try and keep the hours similar
  • Other 10% of time engines are off jigging for bottom fish


Issue With Current Setup

  • After port motor has sat for some time, and the starboard motor was running. If I start the port motor my electronics flicker. My autopilot is on the port motor and looses course when this happens and I have to reset everything.


Proposed Fix

  • Install this battery switch (attached)and ACR. Making one battery my starting battery and the other a dedicated house.
    • The big power draws on the house would be:
      • Two Downriggers
      • Wallas Heater
      • Garmin 1243
      • Garmin 943
      • Garmin VHF


Questions

  • For my use case is this a sufficient setup?
  • What might I not be considering with this setup?
 

Attachments

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You always want to isolate your electronics from the engine starting battery to avoid spikes, low voltages etc during the starting phase from damaging (or having to reset the the auto pilot or worse.

You want the house battery to be isolated from the engine start during loads, and the ACR does that. It also keeps the starting battery from being drained by the house battery.

Where I am going to raise a question about your diagram, is you have both engines directly charging a single engine start battery. That can lead to damage to the regulators or "alternator". Also there is a potential issue of "alternator" output without the resistance of a battery load, which can blow the diodes in an "alternator". The multi battery switch, has "make before break", but in this case, it seems possible to turn the battery off, if the engines are running and cause damage. This may be just in theory...but I would not take that chance.

You can charge the house battery from one of the engine start batteries, or use a switch and two ACR or there could be a case for diodes on one of the two setups.--in any case, you want to keep the electronics isolated from teh start battery. An arguement for the Diodes would be that circuit will not feed back into one of the start batteries, and avoid directly connect them to each other (and in effect the outputs of both engines.

Back to the fuse/circuit breaker--it is required within 7" of the battery on each circuit, except the engine starting circuits. I usually use a large amperage (250 to 500 amp) circuit breaker, but a fuse of comporable size would work. For the house loads, I use a 60 amp breaker, a separate 60 amp breaker for windlass on our size of boats. Also I would put a large fuse between the batteries and a large inverter if you have that to give a source of AC 120 V power. For mains power battery charging I use a 3 circuit battery charger.
 
I went down a different path to protect my primary electronics from voltage spikes or under volt conditions. I purchased a 12 volt DC voltage stabilizer and installed it between my batteries and electronics. This ensures the electronics have a stable 12.4 volts feeding them at all times. Starting the engine does not scramble or cause a restart on my Simrad navigational system.
I have used this for the last 3 years and never had a reboot while starting the engine under normal use. The one I purchased is made by Intervolt model SVS1212050 and has a 5 amp output rating. It is about the size of a deck of cards. Not cheap, but worth it to protect the electronics.
 
I was warned to never start my motor with all of the electronics running. I just switched it off and then back on when I started the motor, which was somewhat of a hassle. My initial change, back when Li was crazy expensive, was one 100 AH 12 VDC with a DC/DC charger between the starter and house battery. I got overvoltage shutdowns of my Garmin equipment when the house battery voltage went high. Shutting off the DC/DC and letting the voltage drop, then shutting off all equipment while it charged was the new pain. Restricting the max charging voltage with a new, programable DC/DC solved that problem, and I was happy until I wanted more storage. Currently, I have a 230 Amp 24 VDC battery and DC/DC charger that incorporates solar, and a 24 to 12 VDC Buck converter. The equipment voltage is almost always showing exactly 12 VDC, which is comforting.
 
thataway said:
Where I am going to raise a question about your diagram, is you have both engines directly charging a single engine start battery. That can lead to damage to the regulators or "alternator". Also there is a potential issue of "alternator" output without the resistance of a battery load, which can blow the diodes in an "alternator". The multi battery switch, has "make before break", but in this case, it seems possible to turn the battery off, if the engines are running and cause damage. This may be just in theory...but I would not take that chance.
Click to expand...
Thank you for the detailed reply. I have read that before on other threads. I have some confusion on this and I probably just don’t understand how the ACR works. Wouldn’t the ACR alleviate the issue of having both engines charge the same battery? Why would Blue Sea recommend such a configuration if that was the case?

Hopefully that didn’t come across accusatory, just genuinely confused as I’ve read conflicting information from two credible sources (you/others and Blue Sea.)
 
Some thoughts about what you have and want.

Two engines point most strongly toward two start batteries in my estimation. They could be downsized to the most compact that will do the job which might save some space and weight if they are currently oversized. 65AH/420CCA is what is recommended for your engines, and the charging output of each is less than 20 amps, so not much concern of overheating a smaller battery. Search for this on Amazon as an example of a smaller profile with the power needed.

Marxon Group 140R Car Battery 12v 50AH 570CCA H4 AGM​


Take all loads off the start batteries and move them to a house battery. Carry a basic jumpstart pack instead of installing wiring to do that on your boat. That way it can be used for another boat or land vehicle more also. They stay charged all season no problem.

Connect one of these small units between each start battery and the house battery/bank and you are taken care of. I have used them for years on multiple boats with no issues.


It would likely be workable to use a single battery for starting both engines but I would upsize it a bit more and still not really feel good about that setup. A single ACR would do the job with that setup of course. Not unsafe, just sub-optimal for a twin setup, and lacking the redundancy you might want to preserve.


Greg
 
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