Bow thruster not producing much thrust

NoRain said:

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.

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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

NoRain said:

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.

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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

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.

Comodave said:

As in post #41…

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Great minds think alike

Bmarler said:

Great minds think alike

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Oh yee.

NoRain said:

. 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.

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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,

I believe you are missing my point completely.

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

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.

Iggy said:

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.

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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.

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.

Thread drift much?

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?

HeadedToTexas said:

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?

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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

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.

O C Diver said:

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.

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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.

Jeff F said:

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.

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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

O C Diver said:

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

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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.