Thruster Battery: Deep cycle or not??

caltexflanc · May 12, 2014

Delta Tango said:
Can I say that Deep Cycle and dual purpose batterys have no place driving DC Bow thrusters. The issues are simple, deep cycle batteries do not deliver cranking amps for anything like the duty cycle required and although some quote outstanding CCA numbers the duty cycle is in some cases less than a second. The other problem with dual purpose batteries including deep cycle is in their in ability to recover - they dont absorb current well and need trickle charging.
In my experience thrusters will fail when the boat owner is returning home after being away and the batteries are down, there is a thought that simply running home is enough to re-charge the banks but that isnt always true.
In a series wound DC motor cranking capacity of your battery and its duty cycle is the only thing that matters.
Sometimes the cheap batterys are the good ones - good old lead acid for me.

Funny thing, Vetus specifies what size battery to use for their thrusters by giving an amp hour (not a cranking amp) specification and range. They also note that if the capacity exceeds the top end of that range, and the cables are larger (or much shorter) than that specified in their table, the usage time must be reduced to avoid motor damage.

Delta Tango · May 12, 2014

caltexflanc said:
Funny thing, Vetus specifies what size battery to use for their thrusters by giving an amp hour (not a cranking amp) specification and range. They also note that if the capacity exceeds the top end of that range, and the cables are larger (or much shorter) than that specified in their table, the usage time must be reduced to avoid motor damage.

Vetus are wrong.
What the issue is with your comment on motor damage is like this - most providers of DC thruster make their specification based on an expected voltage loss. For example, Sidepower quote their performance in KG of thrust at 21vdc, other brands do the same so the run times are based on the voltage / amps = KG of thrust. If you increase the voltage at the thruster you also increase the current; Increase current you increase heat and therefore shorten run times (or potentially damage motor). The offshoot of all that is increase current = increase power with a shorter run time due to all being thermaly protected.
In my experience - Deep Cycle batteries have no place connected to a Bow Thruster of any brand.
I have watched my Clamp Meter tell me the story of just how poor they are 100 times.
DT

caltexflanc · May 12, 2014

voltage / amps = KG of thrust. If you increase the voltage at the thruster you also increase the current;

You really didn't just say that did you? Really?

Vetus is wrong???

Delta Tango · May 12, 2014

caltexflanc said:
You really didn't just say that did you? Really?

Vetus is wrong???

Yes I did, based on your assertion - however I believe its all about how you understand their instructions - just had a look

125 kgf’ - 12 V : 2.5 min. at 840 A

‘125 kgf’ - 24 V : 2.5 min. at 470 A

I read this differently and dont read into it stored amps rather I read this as capability of the battery required to deliver current. They are requesting in my opinion cranking requirements not deep cycle storage.

For the record I dont believe Vetus are incorrect. I have installed and sold many of their product (without problem) as well as Sidepower, C Marine (a good new brand) as well as fixing just about all the rest over the last 20 years or so.

sunchaser · May 12, 2014

Well Ski, amazing the discussion you raised. I must say though, sure glad I have AGMs for the thruster given the batteries' location. Lots more to this than arguing battery types.

FF · May 13, 2014

AC motors (except universal ((with brushes))) eat power in watts. V x A = W

So if the power ,Voltage, goes down yes more amps are required.

Thats why so many air cond refuse to start in summer , low dock voltage can not deliver the watts required for it to run. The Watts are constant, as is the power.

DC and universal AC motors are quite different , feed them 120V and receive a certain HP, feed then 90V (chain saw at the end of 4 extension cords) and the HP is less , as is the amperage drawn.

Thats why they are selected for the task.

A DC windlass is similar , lower the supply voltage and the amperage is also decreased.

caltexflanc · May 13, 2014

These are DC motors and they power in watts too (V x A = watts) . So does your engine (1 horse power = 745 watts). So on an electric motor, to generate the same power, as volts increase current decreases as illustrated in the number of amps in the Vetus specs for 12 and 24 volt versions.

Look down the Vetus manual a few more pages to "The Power Supply" and you will see the battery is spec'd in ah. By coincidence I have the same manual, in mine it is page 16 in the English section.

rwidman · May 13, 2014

Delta Tango said:
Vetus are wrong.

It takes a pretty big pair to say the manufacturer of a piece of equipment is wrong when they specify how to install or use it.

My thruster is a Key Power and it came as original equipment on the boat. It's powered by the house bank which used to be deep cycle batteries but is now AGM which are pretty much deep cycle in operation.

Regardless, it's worked just fine since I bought the boat in 2008.

Billylll · May 13, 2014

rwidman said:
It takes a pretty big pair to say the manufacturer of a piece of equipment is wrong when they specify how to install or use it.

My thruster is a Key Power and it came as original equipment on the boat. It's powered by the house bank which used to be deep cycle batteries but is now AGM which are pretty much deep cycle in operation.

Regardless, it's worked just fine since I bought the boat in 2008.

I'm with you Ron, I have (3) 31 series Lifeline AGM's and the thruster has never let me down. It was installed in 2007.
Bill

FF · May 14, 2014

These are DC motors and they power in watts too (V x A = watts) . So does your engine (1 horse power = 745 watts). So on an electric motor, to generate the same power, as volts increase current decreases as illustrated in the number of amps in the Vetus specs for 12 and 24 volt versions.

TRUE , that is how they are rated for static comparison ,,my point is the HP goes down as the DC voltage decays.

An AC motor will attempt to create the HP by demanding more amps.

A DC motor ACCEPTS the fact that it creates less power with lower volts and does not demand more amps.

ON a DC motor the watts and therefore HP output change , by design.

caltexflanc · May 14, 2014

Low voltage will cause a DC motor to slow down. On a bow thruster, it can cause the solenoids to freeze up. Kind of like your car, sometimes hammering on 'em will help, on my Vetus I had to stick my finger down the hole to loosen it. Yes, I did tell it that it may experience a little momentary discomfort.

Delta Tango · May 28, 2014

DC Bow Thrusters are a series wound electric engine that as the voltage drops so does the amps. Just wanted to correct a few comments above. The constant with the thruster is the torque load at the propeller so with this constant you will only see an increase relative to the torque loading. An example is when the propeller is a bit crusty - it will increase the torque load and therefore the amp draw at a given voltage.
Just the facts.

Billylll · May 28, 2014

I see no harm in using AGM batteries for the bow thruster power. Many boats that is the only type of battery that can be safely installed in the bow. AGM batteries are as close to a dual use battery as you are going to get.
George you are correct low voltage can be a real issue with any DC powered bow thruster. I guess there are installations from aft engines where the thruster wires run from the ER to the bow the round trip distance can easily exceed 60 feet even on a small vessel. This is why I like to see the batteries for the thruster be located within 10 feet round trip in the bow. This applies to stern thrusters, although they are rare compared to the number of bow thrusters.
Bill

Thruster Battery: Deep cycle or not??

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