Bow thruster not producing much thrust

[O C Diver]

Amps don’t get pushed, they get pulled. A battery will only accept as many amps *at a given voltage* as its chemistry and state of charge dictate. You don’t cook a battery by”pushing” too many amps through it. You cook it by supplying too high a voltage for too long, thus allowing it to pull more amps than its design (charge curve) intended.

So you're saying it's impossible to charge a battery at too high an amperage? Sorry not true. Most reputable battery manufacturers have a specific not to exceed charge rate for each of their batteries.

Ted

 

[O C Diver]

I guess the simplest example I could give is a battery at Float. Hook up a 200A charger and set the voltage to 13.4V and (assuming the start battery is full as in the example given) there will be no current flow. The battery is full and it cannot accept any more current at that voltage. If you ran the voltage up to 15V then there would be current flowing into the battery, and then the battery would start gassing, and that-there is bad things happening. Run it up to 16V and you’re into Equalization mode, which is a fancy term for controlled boiling. Actually intended for FLA batteries only although a couple manufacturers (eg LifeLine) employ it in a very limited and controlled way in their AGM liline.

A better example would be a bank of Trojan T-105. Lets assume they're at 12 volts or less. Lets assume they are a bank of 6, each pair in series to make 12 volts, and 3 pairs in parallel. The bank is approximately 675 AH. Trojan's not to exceed charge rate is 15%. At 12 volts, a multistage regulator will run wide open in bulk phase until it reaches target voltage, where it switches to absorption. So, instead of charging at 101 amps (15% of 675), it now charging near 30%. Not difficult to over charge (amps) an open lead acid battery with a big alternator and a multi stage regulator.

Ted

 

[NoRain]

Hi Ted, that’s actually not a better example, it’s quite a different scenario than I was responding to in your post #52. I believe the scenario there was concern over exposing an almost fully charged start battery to a 200A charging source. Further, this would occur because an ACR closed paralleling the start battery to the house bank. Do I understand that correctly? If so, then what I said is true — the almost full start battery would only accept a small amount of current. Increasing of course as the voltage of the now paralleled banks would increase due to the charging of the house bank. The house bank would consume the lion’s share of the available charge current, up to the 200A max that was mentioned. The start battery would be exposed for a period of time to a higher than desirable charge voltage, but this would not be tragic….depending of course how long and for how many times. So in that scenario, with an almost full start battery you cannot push any more current into it, it is full. (Disclaimer: not without doing something you shouldn’t be like raising the voltage to an unreasonable number).

The scenario you just described in #62 is very different, a 50% SOC battery, and you’re quite right an overcharging possibility exists. But as you know this is a complicated subject and difficult to discuss in anything less than 500 word epistles without making some assumptions. First, that recommended # from Trojan is not an arbitrary #, it is based on the fundamental concern of not cooking the battery. ie as KnotYet said, absorbing energy and turning it to heat. You can in fact charge at a much higher rate as long as you are monitoring the battery temperature to ensure you stay below gassing voltage (approx 2.4V per cell). And once you reach that level (14.4V) you should be back down to the .2C recommendation (varies some by manufacturer). There are temp sensors for shore chargers and alternators that can regulate the max current available to ensure that doesn’t happen.

 

[Bmarler]

As in post #41…

Great minds think alike

 

[Comodave]

Great minds think alike

Oh yee.

 

[more]

. If you ran the voltage up to 15V then there would be current flowing into the battery, and then the battery would start gassing, and that-there is bad things happening. Run it up to 16V and you’re into Equalization mode, which is a fancy term for controlled boiling. Actually intended for FLA batteries only although a couple manufacturers (eg LifeLine) employ it in a very limited and controlled way in their AGM line.

who is stupid to run alternator 15-16v. every factory made alternator maintain (13,8)14.05 up to 14.4V . with cable loss you have on battery 13,5-14,05. if alternator produce 15-16V is broken and need repair. alternator is not made to Equalization,for this go on marina and shore power and proper charger.
you and other think product like this Universal External Voltage Regulator 13.4v-16.2v - AD alternators
is good. i don't suggest nobody use this if you don't understand how from scratch how in house make lithium,agm cell. you have 100 kg lead,touch sulfur acid and make battery. USA farmer before ww1 make own battery in barn,

 

[NoRain]

I believe you are missing my point completely.

 

[Comodave]

Boy, this thread has gone way out in left field.

 

[Iggy]

Very interesting topic on push and pulling of amps.

I would agree with both of you but I am not that smart. One way I look at it is. In charging, the battery is the load. Voltage goes up, current flows.

You turn on a light, again current flows. So it sounds like amps are being pulled towards the load, yes? Bottom line, it works.

Off topic -- There is a YouTube video of this physicist stating that its the magnetic field around the wire that carries the current, not the electrons.

 

[KnotYet]

Very interesting topic on push and pulling of amps.

I would agree with both of you but I am not that smart. One way I look at it is. In charging, the battery is the load. Voltage goes up, current flows.

You turn on a light, again current flows. So it sounds like amps are being pulled towards the load, yes? Bottom line, it works.

Off topic -- There is a YouTube video of this physicist stating that its the magnetic field around the wire that carries the current, not the electrons.

In a sense, the electron flow is a result of the field or current.
A field exists first and the electron flow is induced and 'carry' the field with them.
Not pulling or pushing so much as going with the flow.

 

[Delta Riverat]

Current flow is like heat or fluid flow. Current flows from high potential (voltage) to low. Heat flows from high temp to low. Fluid flows from high (pressure) to low.

Easy.

 

[Bmarler]

Thread drift much?

 

[HeadedToTexas]

Interesting debate.

For better or worse, our haul out arrived before I could test voltage at the thruster motor. I did however confirm that tunnel or prop fouling was not the culprit. This is before and after power washing.

More as I know it, though that likely won't be until May 2025. I am tempted to make the wiring modifications without knowing about the voltage results since running the thruster and windlass off the start battery just makes more sense to me. Thoughts?

 

[O C Diver]

I am tempted to make the wiring modifications without knowing about the voltage results since running the thruster and windlass off the start battery just makes more sense to me. Thoughts?

I think the concept is good, and there will certainly be an improvement. It would certainly have been nice to make comparisons on voltage sag. Have you determined that after the wiring change, alternator voltage will be elevating the start battery voltage? A volt or more can make a significant difference in bow thruster performance.

Ted

 

[Jeff F]

I'd advise reading the manufacturer's advice, and then rereading this thread.

Voltage sag under thruster demand comes from two sources - battery voltage sag (CCA allows 7.2v) and cable loss. If you want peak performance you need a strong starter bank as close as possible to the thruster.

 

[Jeff F]

4.7 KW (4,700 watts) ÷ 12 volts = 392 amps. From recollection, a DC motor running at below rated voltage shouldn't require more amps, it should slow down.

Even more keen to know how much of a voltage drop you're getting.

Ted, not disagreeing with your math. But realistically the thruster never sees 12v.

My curiousity about this was satisfied recently when I noticed that one major manufacturer rates their thruster based on a lower voltage - something like 21.6v on a 24v rating.

Vetus seems to consistently quote 100a/kw through their 12v range, so they may be using 10v as their nominal voltage, or something in that vicinity. That would be realistic with LA batteries.

 

[O C Diver]

Ted, not disagreeing with your math. But realistically the thruster never sees 12v.

My curiousity about this was satisfied recently when I noticed that one major manufacturer rates their thruster based on a lower voltage - something like 21.6v on a 24v rating.

Vetus seems to consistently quote 100a/kw through their 12v range, so they may be using 10v as their nominal voltage, or something in that vicinity. That would be realistic with LA batteries.

Not sure what you're trying to say.

I understand your point about what the bow thruster sees under load (the key phrase). But if you start with 12 VDC at the battery and see a under load voltage of 9 VDC, it would be better to have 13 VDC at the battery (with the alternator producing) and 10 VDC under load.

Ted

 

[Jeff F]

Not sure what you're trying to say.

I understand your point about what the bow thruster sees under load (the key phrase). But if you start with 12 VDC at the battery and see a under load voltage of 9 VDC, it would be better to have 13 VDC at the battery (with the alternator producing) and 10 VDC under load.

Ted

My point was that the manufacturer likely gives a rated output based on an expected voltage of less than 12v. So a 4 kw motor may have an expected working voltage of 10v and a design draw of 400a.

Taking a motor's rated output and dividing by 12 to get design amperage may understate the current by 10-20% if that's true.

 

[HeadedToTexas]

I finally got ahold of Vetus and their support rep said that the motor is rated for 4400 watts (4.4 kW or 6 hp) at 12 volts. He explained that the minimum voltage at the motor I should see under load is 10.6 VDC. His suspicion is that pulling 600 amps for several second at a time has fatigued the batteries more than I expect and that is why the thruster seems to produce less thrust than it used to. My 5 year old AGMs may be okay for powering the DC fridge, running the water pumps now and then, and making coffee on the inverter in the morning, but not okay to keep the voltage around 12 when the thruster is pulling 600 amps.

He also recommended not powering the thruster off the engine start battery with a Cummins QSB as it has a solenoid that can kill the fuel pump if the voltage drops below 12 volts. The best bet is to upgrade the house bank if volts are low, or add a battery dedicated to the thruster.

You guys have also said these things, so this is just an update on the feedback from Vetus.

I asked about the 6 blade prop producing more thrust than my 17 year old 3 blade prop. He said it would, but not enough to notice that the thruster is no longer moving the bow of the boat. Almost certainly an electrical issue.

 

[KnotYet]

I finally got ahold of Vetus and their support rep said that the motor is rated for 4400 watts (4.4 kW or 6 hp) at 12 volts. He explained that the minimum voltage at the motor I should see under load is 10.6 VDC. His suspicion is that pulling 600 amps for several second at a time has fatigued the batteries more than I expect and that is why the thruster seems to produce less thrust than it used to. My 5 year old AGMs may be okay for powering the DC fridge, running the water pumps now and then, and making coffee on the inverter in the morning, but not okay to keep the voltage around 12 when the thruster is pulling 600 amps.

He also recommended not powering the thruster off the engine start battery with a Cummins QSB as it has a solenoid that can kill the fuel pump if the voltage drops below 12 volts. The best bet is to upgrade the house bank if volts are low, or add a battery dedicated to the thruster.

You guys have also said these things, so this is just an update on the feedback from Vetus.

I asked about the 6 blade prop producing more thrust than my 17 year old 3 blade prop. He said it would, but not enough to notice that the thruster is no longer moving the bow of the boat. Almost certainly an electrical issue.

I don't see where you derived 600 amps but even 366-415 amps is a fairly heavy load.

 

[HeadedToTexas]

I didn't either and did not check his math at the time, but you are right that 4400 ÷ 12 = 367 amps is still quite a load through all that wire.

 

[O C Diver]

Lot to be said for a battery at the bow thruster.

Even more to be said for a 24 volt motor and 2 smaller batteries in series at the bow thruster.

Ted

 

[HeadedToTexas]

If it gets to that point, I will be joining the 24 volt bow thruster group. Do you use a DC to DC charger to maintain that 24 volt bank?

 

[Comodave]

I have 4 thruster batteries, 2 at the bow and 2 at the stern. Short cables and each thruster has its own charger. Works great. Have you checked every connection?

 

[Comodave]

If it gets to that point, I will be joining the 24 volt bow thruster group. Do you use a DC to DC charger to maintain that 24 volt bank?

I just use a dedicated 120 volt charger for each thruster bank. I haven’t ever discharged the thruster batteries enough that I can’t wait until we are plugged into shore power to recharge them. That way I don’t have to run DC power cables for long distances.

 

[O C Diver]

If it gets to that point, I will be joining the 24 volt bow thruster group. Do you use a DC to DC charger to maintain that 24 volt bank?

Below is a picture of my bow thruster conversion to 24 VDC. I used a 6 amp two bank 12 volt battery charger. While there are a lot of amps driving the bow thruster, the pulses are very short. Simply, your refrigerator consumes more watts per hour than your bow thruster, unless you use it in place of your rudder. I went with 4/0 battery cable for the incredibly long runs, mostly because it was orphan cable.

The battery charger draws negligible power when the batteries are full. So, I wired it to one of my inverter circuits to charge while underway. It's transfered automatically to shore power when at the dock or running the generator.

This is an identical charger that maintains the generator and engine batteries.

Ted

 

[Jeff F]

My point was that the manufacturer likely gives a rated output based on an expected voltage of less than 12v. So a 4 kw motor may have an expected working voltage of 10v and a design draw of 400a.

Taking a motor's rated output and dividing by 12 to get design amperage may understate the current by 10-20% if that's true.

One more thought - Vetus likely rates output power. Not sure what efficiency is, but that would also indicate higher current.

Getting back to batteries, I think most people don't realize how much the battery voltage drops under load with LA batteries.

Below is the first thing Google brings up, and it says that a battery that supplies 9.6v at 1/3 CCA passes a load test.

ETA: going to 24v doesn't change this challenge.

Load Testing Your Battery

Use this same procedure for VRLA DRY CELL batteries and Flooded batteries: Recharge if the open circuit voltage is below 75%. If you have an...

discoverbattery.com

Forget cable loss. Getting 10.6v from a LA starting pack @400a isn't a trivial challenge.

 

[tiltrider1]

I just upgraded the boat to a 24v thruster. I used two AGM Group 41 batteries in series. For charging I used a 24v 15 amp AC charger. I rarely use any thruster to get off a dock so see no need for charging while under way. Once on a dock the charger usually has 24 hours to recharge which is more than enough to replenish the bank. The 24v charger was only $59

 

[Comodave]

I just upgraded the boat to a 24v thruster. I used two AGM Group 41 batteries in series. For charging I used a 24v 15 amp AC charger. I rarely use any thruster to get off a dock so see no need for charging while under way. Once on a dock the charger usually has 24 hours to recharge which is more than enough to replenish the bank. The 24v charger was only $59

That is what I did when I installed mine except I used a $500 Promariner 20 amp charger, oh well…

 

[tiltrider1]

That is what I did when I installed mine except I used a $500 Promariner 20 amp charger, oh well…

We’ll see how long my charger lasts. I figured it was worth a try but I won’t be surprised if I end up with a more expensive marine charger.