Bow Thruster drains battery even when off!! And it's normal!

Apr 14, 2010
195
Jeanneau 42DS Larnaca Marina
I was leaving my boat with everything OFF including the charger thinking it was not necessary and preventing any zinc usage by unplugging the shore power. After returning in 2-3 days, I would find that the Starting battery was below 12V with the alarm flashing while the House battery had it's full charge. mmmm major issue here and a challenge to identify problem. I spend hours taking volt reading at all different locations and with different switches on and off. I thought maybe was the windlass contactor sticking but that was not it. It turned out that it was the Max-Power Thruster Control Box (not the panel at the helm) which is powered (as per manual) by a separate battery than the thruster and it only has an 8A breaker. The thruster battery is a dedicated one sitting right next to the motor without a way to disconnect it. It has a 200A fuse but not a breaker. So even when you think that the thruster of OFF by turning it OFF at the helm, the Control Box contactor is still active and using some power from the "other" battery, in my case the Starting battery and that's why it was being drained. Turning the 8A thruster breaker OFF will prevent this by cutting power to the control box...but who would think that! I have the option of connecting the control box to the house bank instead of the starting bank to prevent accidental draining while sailing but I could introduce another problem to the house bank. I have to really think about it before I do it.
So when you turn the engine off and enjoy sailing, be aware that the thruster control box still needs power unless you turn off this breaker or the battery supplying it. Just thought I would share this experience with those who like to turn off the charger for the winter.
 
Last edited:
Nov 26, 2012
1,653
Hunter 34 Berkeley
Seems not right. I am by no means an electrical expert but a bow thruster that drains the batteries all the time is faulty in some way. Has to be.
 
Last edited:
Sep 20, 2014
1,320
Rob Legg RL24 Chain O'Lakes
The easy solution is to just use a 12 volt latching solenoid rated for continuous duty. This is what I use in the motorhome. When I walk out the door the last time, I hit the button and the battery is disconnected. This way I know there is nothing discharging it.
 
Dec 19, 2006
5,809
Hunter 36 Punta Gorda
I think there should be a power breaker and in between the the power circuit breaker should be
another type circuit breaker that pops if a over load or short happens before the thrusters.
But I think nothing should be draining a windlass or thruster when no being used that is for sure,
check these batteries that they are good.
Nick
 
Apr 27, 2010
966
Beneteau 352 Hull #276 Ontario
I don't know what model you have or if it was factory installed, but if you look at a sample electrical diagram from max power, they show a switch to the control box. Maybe you have a spare breaker on your electrical panel?
Good luck
 

Attachments

  • Like
Likes: Ron20324
May 24, 2004
7,129
CC 30 South Florida
Bow thruster is non essential; just install a breaker switch to cut all power to unit until it is needed. When the boat is docked I keep shorepower On all the time. Sacrificial Anodes are inexpensive and their wear is not exclusively controlled by your electrical system. House batteries need to be charged after every outing for longevity and due to battery charge absorption rates it takes between 2 to 5 hours to bring them to 100%. No need to sit around watching batteries charge. I also like to have fully charged batteries when I show up next time to the boat and there is some evidence that if you run refrigeration constantly the unit will last longer. Having cold beer is just a side benefit.
 
Last edited:
Dec 29, 2008
805
Treworgy 65' LOA Custom Steel Pilothouse Staysail Ketch St. Croix, Virgin Islands
There is no way a thruster putting a constant load on a battery is “normal”.
 
Last edited:
Apr 14, 2010
195
Jeanneau 42DS Larnaca Marina
I don't know what model you have or if it was factory installed, but if you look at a sample electrical diagram from max power, they show a switch to the control box. Maybe you have a spare breaker on your electrical panel?
Good luck
Yes I do have a switch below on the panel, as I mentioned in my posting...but you have to turn it off when sailing and remember to turn it back on before you need to thruster.
 
Apr 14, 2010
195
Jeanneau 42DS Larnaca Marina
There is no way a thruster puting a constant load on a battery is “normal”.
It's normal and per installation manual...unless you remember to turn the control box breaker below OFF. The point here is to not think that by turning the thruster panel OFF at the helm everything is OFF. Go below and turn off the breaker too unless you are out for a short sail.
 
Dec 29, 2008
805
Treworgy 65' LOA Custom Steel Pilothouse Staysail Ketch St. Croix, Virgin Islands
It's normal and per installation manual...unless you remember to turn the control box breaker below OFF. The point here is to not think that by turning the thruster panel OFF at the helm everything is OFF. Go below and turn off the breaker too unless you are out for a short sail.
Ok, normal for them - just silly. I can think of no useful purpose for it drawing power other than when it is engaged. Thankful ours does not draw any power until the joystick is pushed left or right...
 
Last edited:
  • Like
Likes: capta
May 17, 2004
5,032
Beneteau Oceanis 37 Havre de Grace
What strikes me is that it seems to be drawing a significant amount of current, not just a small nuisance parasitic draw. To take your started battery down under 12V in 2 days is probably about an amp. That really is territory of "we designed this thing to be off when not in use", unlike a device like a bilge switch or alarm.
 
Apr 14, 2010
195
Jeanneau 42DS Larnaca Marina
Ok, normal for them - just silly. I can think of no useful purpose for it drawing power other than when it is engaged. Thankful ours does draw any power until the joystick is pushed left or right...
I'm not convinced that you are correct on your assumption. Have you verified that? In order for the joystick to be ready, a contactor must be pulled in the control box, which takes power from a battery other than the thuster's. If you go below and turn the thruster breaker on and off you will probably hear the sound of the contactor under the bow bed click...
 
Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
The thruster battery is a dedicated one sitting right next to the motor without a way to disconnect it.
Any battery big enough to power a thruster needs a battery switch under ABYC standards.. Max Power usually recommends an electronic battery switch but a manual switch would meet ABYC standards.. With this switch in the OFF position there would be no power to the thruster. The control box should shut off automatically after a period of no use (can't remember the duration but it is pretty short). There should be no way to be killing the bank the controller is connected to if it is operating correctly. It sounds like something is not wired correctly..?
 
  • Like
Likes: capta
Sep 24, 2018
2,549
O'Day 25 Chicago
The controller for the thruster could have a partially blown output transistor. I've seen this many times with audio amplifiers. One channel will max out well before the other even though they have the same signal. It's like having a water valve that doesn't close all the way. Do you have a way to test if it's drawing more power than usual at various throttle positions? If it's significant I'd fix it. Otherwise I'd just throw a switch or relay on it since it's non-essential and not used all the time
 
Dec 29, 2008
805
Treworgy 65' LOA Custom Steel Pilothouse Staysail Ketch St. Croix, Virgin Islands
I'm not convinced that you are correct on your assumption. Have you verified that? In order for the joystick to be ready, a contactor must be pulled in the control box, which takes power from a battery other than the thuster's. If you go below and turn the thruster breaker on and off you will probably hear the sound of the contactor under the bow bed click...
Well, I can tell you that MY Max Power thruster is dead until the joystick completes the circuit by pushing it left or right. The switch (joystick) closes the circuit to the controller relay, which energizes the thruster. When I turn my battery switch on or off, there is no relay sound. There is no other breaker. Maybe my 18 year old unit isn't as fancy as other newer ones are, don't know. But, as Maine says in his post, "With this [battery] switch in the OFF position there would be no power to the thruster." That's how mine works. The battery switch is between the batteries and the thruster.
 
Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
Well, I can tell you that MY Max Power thruster is dead until the joystick completes the circuit by pushing it left or right. The switch (joystick) closes the circuit to the controller relay, which energizes the thruster. .
Just my 2 cents, but it seems like a thruster is like a windlass, but goes left/right instead of up/down. It seems the wiring should be the same? But maybe not. I'm learning here, too.
 
Last edited:
May 20, 2016
3,014
Catalina 36 MK1 94 Everett, WA
I think most missed the part where the control wiring was specified to go to the house battery rather than the thruster batteries. This implies that the control is a bit more sofisticated than a bang bang control. My guess is it provides some sort of PWM signal to the motor controller (not contacter) to provide variable thrust. The PWM and motor controller could draw substantial power ( it would be interesting to see recommended fuse for that line).

Any way I don’t see how it’s much different from having an autopilot (from gross circuit perspective) - I always turn mine off when not using it.

Les
 

MitchM

.
Jan 20, 2005
1,011
Nauticat 321 pilothouse 32 Erie PA
our maxpower bow thruster was powered off the engine battery and thus was only run with engine on. a joystick at the helm controlled it. there was a large dedicated rotary cutoff switch for the thruster, which we never used unless we were working on the thruster. in all 15 years of use, our thruster never created a parasitic drain on our engine battery as per our logs which recorded engine battery and house bank voltages.