Electrical Brownout When Starting Motor

[Paul D.]

I had only one issue with my new hybrid autopilot I installed last year. It is a new Raymarine EV 200 ACU, EV Sensor core and P70 control head hooked up to the wonderful old Benmar rotary power drive. It steered beautifully last year from flat calm to 37knots with a pretty good seaway.

Problem comes when sailing with the autopilot and starting the motor. The autopilot briefly shuts off, control head shows the improperly powered off message and then it sets itself up again. This never happened with the old 1980's Benmar Cetec control so I reckon the electronics are more sensitive now. I can't imagine this is a good thing to happen regularly so I would like advice to even out the electrical flow during an engine start, at least to that circuit.

I generally start the motor with the battery switch on ALL and then switch to the house battery after motor is running. This brownout has also occurred when I started with the battery switch on the start battery too. The pilot is wired on an instruments circuit with the only other navigation instruments being ST60 Depth and Speed units. The shutdown occurs despite whether the pilot is steering or in standby mode.

Is there a simple solution to even out the voltage during a start that doesn't involve a total rewiring?

New Autopilot control head


Old Belowdecks Rotary Drive

[Maine_Buzzard]

I was all set with a reply about not starting on both, and then saw that it happens on start battery only.

Likely the electronics are just more sensitive, have you discussed this with the manufacturer?

It would also be a good time to have a skilled boat electrical tech review the installation and your battery wiring. You may have a hidden problem in the primary cables causing voltage drop on starting.

To see if it is related to the wiring, try running power to the autopilot straight from the starting battery (with a fuse) and start the motor. If it does not reset, there may be a line drop from the wiring. If it resets, load test both batteries to evaluate their condition.

If it's just sensitive electronics, the solutions I know of are not ABYC reviewed. If the autopilot is actively steering when starting the engine, it needs 5-15 amps of electricity while the voltage is under load.

Having a dedicated gel cell battery (20-35AH scooter sized) tied to the switched power for the instruments and a off-1-all-2 switch would let you power the instruments independently and charge the battery with the engine running.

http://www.ebay.com/itm/BATTERY-SWITCH- ... 1512032174

http://www.ebay.com/itm/Casil-12v-35ah- ... SwnHZYRxWY

Connect the instruments circuit breaker load side to Bat 1, the gel cell to Bat 2, and the autopilot and other instruments to Common. To start the engine, you would set the switch to 2 (standalone gel cell) and kick it over. With the engine running, switching to all would charge the gel cell. Off will isolate everything. Bat 1 setting will power the instruments and isolate the gel cell.

Fusing will be an issue, it will need a fuse at the gel cell (10-20A) and downstream for each device that needs to be protected. Some electronics may still have their inline fuses, so careful checking is required.

On a side note, this would be like a kicker outboard for your nav setup. If something should wreak havoc on your start and house batteries, the gel cell could power the GPS for a day.

Again, ask the vendor and consult with an ABYC competent tech about any changes- I'm mapping out a possibility, but have not actually done anything like this on a boat. Free internet advice is worth its cost.

[bottomscraper]

Make sure all your battery connections are clean and good. E=I*R Your starter draws a significantly higher current "I" than your electronics. If you have any significant resistance "R" in your battery wiring (both positive and negative) you will have significant voltage "E" drop when the starter is being used.

[Maine Sail]

Could be a number of issues:

#1 Weak batteries

#2 Too small a house bank to avoid brown outs during starting. A good sized healthy house bank 300Ah+, for a 33' vessel, should easily start most any small AUX diesel without causing brown outs.

#3 Improperly wired electronics. Your + & - takes offs should always come from as close to the house battery bank as possible. A mistake far too many make is to tap into existing circuits or use the engine block as a negative path for electronics. This can result in not only brown outs but also voltage transients. Sensitive electronics should always have their take off points coming from as close to the bank as possible. if I had a dime for every electronics wiring job that used the engines ground point or starter neg cable as a path back to the bank I be retired... D'oh....

#4 The battery switch is too far from the bank and the wiring is too small. Battery switches should be installed as close to the bank as possible.

#5 Corroded terminations, poor crimps, or undersized wiring.

#6 Incorrect lug stacking leading to voltage drop. Highest current load lug/terminal goes on the bottom. For example if your house panel runs off 4GA wire and your starter is 1/0 you don't stack the 1/0 wire on top of the 4GA wire at the "C" post of the battery switch.



Remember, it does not matter which bank or switch position you use with a 1/2/BOTH switch because your electronics will always be connected to that bank when starting the motor.

There are many paths to fix this but it really should not be happening, in an otherwise healthy system, and is most likely driven by one of the above points..

[Bill Goldsmith]

Paul,

In the generic factory wiring setup, the off/1/all/2 switch governs which battery(ies) is/are being called on to handle the entire load, starting and house. If you have labels indicating that one battery (assume #1) is the start battery, and the other (assume #2) is the house, those designations do not isolate the starting load from the other circuits--they only remind you which battery you want to switch off after the starter is finished doing its job.

The only way to be sure to avoid the brownout (aside from following the other helpful suggestions here) is to completely isolate the starting circuit. I did that on Loonsong. I have a separate on/off switch for the start bank and a separate one for the house bank. That way, when starting, it does not draw any current from the house bank. I installed a battery combiner that kicks in when shore or engine charge current is present, but separates the batteries when not charging. I also installed an emergency combiner switch in case I need to pull the house bank into the starting circuit. But I've never had to use it since I did the re-wire.

It's a lot of work to reconfigure but provides peace of mind. Some of the other suggestions here would be good to follow if you are not in the mood to re-wire the panel.

[Paul D.]

Thanks for these suggestions. I will have some more time to ponder this solution through the long, but getting shorter, Minnesota winter.

I forgot to mention that the autopilot has an old push-pull switch in line from the panel to the ACU. It was there because the old Benmar had no off or standby on the control head. I wondered if this could introduce some voltage drop. Though, it does not have noticeable corrosion on it. Anyway, I had planned to remove it entirely.