pvb
Well-known member
I think I'll agree with Halcyon's professional opinion.
How big should my starter motor fuse be?
- Thread starter demonboy
- Start date
I think I'll agree with Halcyon's professional opinion.
jimbaerselman
New member
Picking up just the windlass point.
If your windlass is going to pull more than 60a, it's usual to feed it from the starter battery rather than the domestic (assuming the domestic bank is designed for AH capacity, rather than cold cranking amps - CCA). Domestic batteries are good at capacity, but poor at delivering amps (rapid voltage drop with time).
As to fusing windlasses, on a long cable run to the windlass, large diameter cables are needed to keep voltage drop low, so they are most unlikely to overheat before the motor melts down. However, a local thermal switch is needed to prevent the windlass from melting down through overload. At the supply end, the only threat is the possibility of a cable short through chafe or maintenance accident. An most unlikely event, but you may wish to guard against it.
Rather than big lengths of heavy cable between battery and windlass, many install a high CCA (starter type) battery close to the windlass, fed with light weight charging lines which carry low re-charging amps. With a bow thruster, this makes even more sense.
jimbaerselman
New member
Vic,
I think when looking at protection against a maintenance accident or chafe, it's perhaps appropriate to look at what the battery could deliver. I'm guessing here, but I imagine a battery spec for the above motor would ask for about 500 CCA - which means it could push well over 1,000a for a short time.
Are simple fuses reliable enough to distinguish between a demand of 500A and 1000A over (say) five seconds? You don't want nuisance blows!
ianj99
Active member
That's fine, but personally I'd spend the money on an automatic firextinguisher system for the engine compartment because if there is a fire, there's far more chance of a cause other than a short in the starter circuit...
I'm surprised some owners ever put to sea with all the 'health & safety gone mad' issues that could endanger them!
ianj99
Active member
This takes us back to my original post where I suggested that the battery cables be uprated closer to the fuse rating if one is fitted otherwise the cables and/or terminations become the fuse rather than the fuse itself.
Even if the copper of the cable survives, its insulation may in its entirety, not, so whilst the fuse may eventually blow, the cables may still need replacing.
So either fit a fuse and uprate the cables or leave well alone, having first inspected the routing for chafing and terminations for signs of overheating due to bad or loose connection.
pvb
Well-known member
This isn't necessarily as simple as it sounds. In operation, the bow thruster can draw a considerable current through the charging wires - especially if the engine's running and therefore the voltage in the charging wire is 14.5 or so. Consequently, these "light weight charging lines" need to be fairly heavy. They also need to be protected with fuses/breakers at both ends of the wire. When the cost is added up, it's usually cheaper just to run heavy cables from the main battery.
jimbaerselman
New member
I agree it's not so simple. But the charge rate can be limited by using a DC to DC charger, useful for a second or third battery which uses very few AH (albeit, high brief battery currents).
pvb
Well-known member
True, but again the cost is escalating. The simple "big wire" solution is often the best unless access for routing cables is very poor.
demonboy
Active member
Interesting debate!
@Jim - my windlass has been wired to my starter battery and even with the engine on it would frequently trip. I then added a 70aH battery right next to the windlass so I ended up with 170aH on my starter circuit with the ability to isolate the windlass battery when not in use and when not charging. This appeared to work but I then had the problem of mismatched batteries being charged. Ultimately, however, the 70aH battery got destroyed by the condition in which it was located (the result of a couple of monsoons). I am now thinking of putting the windlass on my domestic circuit.
@Ian - I already have a fire extinguisher in my engine compartment so I don't believe it is an either/or scenaio with the fuse. As long as there are no compelling reasons NOT to install a fuse (i.e. that it increases the risk of a short/fire) I aim to do so. I think pvb's comparison with fire extinguishers and lifejackets makes fitting a fuse a no-brainer, irrespective of what I am legally required to have.
@Jim - my windlass has been wired to my starter battery and even with the engine on it would frequently trip. I then added a 70aH battery right next to the windlass so I ended up with 170aH on my starter circuit with the ability to isolate the windlass battery when not in use and when not charging. This appeared to work but I then had the problem of mismatched batteries being charged. Ultimately, however, the 70aH battery got destroyed by the condition in which it was located (the result of a couple of monsoons). I am now thinking of putting the windlass on my domestic circuit.
@Ian - I already have a fire extinguisher in my engine compartment so I don't believe it is an either/or scenaio with the fuse. As long as there are no compelling reasons NOT to install a fuse (i.e. that it increases the risk of a short/fire) I aim to do so. I think pvb's comparison with fire extinguishers and lifejackets makes fitting a fuse a no-brainer, irrespective of what I am legally required to have.
mitiempo
Member
I agree a fuse is cheap insurance.
As far as a windlass, I prefer to wire from aft, usually from the domestic bank, with the appropriate sized cables and fused at each end. . A thruster can have a battery forward and charged through smaller cables, eg with an Echo Charge, if desired as it is used for only a few moments each time. I don't believe it makes sense with a windlass. There may be times when you have to re-anchor several times to get it to set and a windlass battery forward charged through small gauge cables may not be able to keep up with the repeated use.
A neighbour had a windlass foot switch short out when he was away for a few days - there was no fuse installed and the repair was over $10,000. While not a start cable any wire can cause a lot of damage if it comes loose or chafes on something.
As far as a windlass, I prefer to wire from aft, usually from the domestic bank, with the appropriate sized cables and fused at each end. . A thruster can have a battery forward and charged through smaller cables, eg with an Echo Charge, if desired as it is used for only a few moments each time. I don't believe it makes sense with a windlass. There may be times when you have to re-anchor several times to get it to set and a windlass battery forward charged through small gauge cables may not be able to keep up with the repeated use.
A neighbour had a windlass foot switch short out when he was away for a few days - there was no fuse installed and the repair was over $10,000. While not a start cable any wire can cause a lot of damage if it comes loose or chafes on something.
halcyon
Well-known member
It is simple, a small VSR that is interfaced to the windlass, run the windlass, drop out the VSR, turn off windlass re-engage VSR.
Fit 20 watt solar panel, bow battery is always topped up, VSR gives back-up charge from engine, main solar panel bank, and mains charger.
Whatever you fit you need fuses to protect the cable, you cannot rely on taking out the main fuse and all power on the boat, for a windlass fault.
Brian
jimbaerselman
New member
When running from your starter battery, which end caused the trip? The thermal cut-out at the working end? or the supply circuitbreaker/fuse at the battery end? I'll ignore the possiblity of an under-powered winch, but a low voltage at the winch (voltage drop due to too light wiring) slows the winch and increases it's current consumption, causing premature thermal trips. If adding the local battery removed that problem, that confirms the cause . . .
Balanced charging of multiple banks is always a bugbear on smaller boats. With a single 3 stage controller, you can match charging output to one bank, but others take pot luck. Switch controllers help, as can multiple output controllers. It's that poor little box of acid up front which suffers most though. If it's paralleled with the starter battery back astern, it's always going to get less than it's fair share of charge. That's why I went for DC to DC chargers - one for the starter, one for the windlass.
I kept windlass off the domestic bank in order to avoid the high voltage drop when it's used. My plotters tripped . . . just what you don't want when setting off at night with a tight bit of pilotage ahead. But perhaps they're much better at resisting voltage drops nowadays!
Edit: my "switch controller" = Halcyon's "VSR" I think - Voltage Sensed Relay?
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2Tizwoz
Well-known member
Protect your boat with the correct size wire and fuse
From the bluesea.com website
The motor current question has already been answered here for instance
Instantaneous currents are handled partially by the thermal mass of the wire and fuse. However if the engine doesn't turn over for some reason a protective fuse may blow. Which is no bad thing.
From the bluesea.com website
The motor current question has already been answered here for instance
Instantaneous currents are handled partially by the thermal mass of the wire and fuse. However if the engine doesn't turn over for some reason a protective fuse may blow. Which is no bad thing.
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ffiill
Active member
Starter motor fuse?-thats a new one on me-starter motors in my experience are wired live to battery-or do you mean on the relay circuit.
Do recall an incident however many years ago on a Ford Thames van which had a live push button starter switch next to drivers seat.I dropped something on switch whilst van was parked up and in gear-relsult a melted starter motor.Being a poor student I then got it home to Yorkshire from Skye with bump starts and its starting handle!
Do recall an incident however many years ago on a Ford Thames van which had a live push button starter switch next to drivers seat.I dropped something on switch whilst van was parked up and in gear-relsult a melted starter motor.Being a poor student I then got it home to Yorkshire from Skye with bump starts and its starting handle!
ianj99
Active member
I've tried to get this across, and even the US Coastguard doesn't require one, nor do Insurance companies, but its like talking to a brickwall the way some stubborn old fools won't listen....
Still its their money and hassle when their starter fuse blows at the wrong moment.
Ian
pvb
Well-known member
I've tried to get this across, and even the US Coastguard doesn't require one, nor do Insurance companies, but its like talking to a brickwall the way some stubborn old fools won't listen....
OK, so as I read it, you're saying that prv, savageseadog, lenseman, David2452, MrCramp, halcyon, mitiempo, 2Tizwoz and I are all "stubborn old fools". An interesting theory, but I'm afraid you're wrong again.
ianj99
Active member
Sorry, but the rules and regs governing the fitting of starter circuit fuses are not made by anyone on this forum.
I would therefore consider it foolish and arrogant for anyone on here to presume to know better than the Regulators.
mitiempo
Member
If the main switch you have for your battery banks is a 1/2/both/off switch that means both banks are either domestic banks or starting banks and ABYC require fuses on each. If your switching arrangement is not this way fusing is just common sense.
I think anyone who has seen the results of a chafed battery cable would fuse wherever it made sense.
I think anyone who has seen the results of a chafed battery cable would fuse wherever it made sense.
SimonPembs
New member
Hi all,
I have just found this conversation after joining today.
I work in the commercial boat sector and have worked in the leisure sector too, for many years.
I have never seen a engine starter motor protected by a fuse or circuit breaker, NEVER. It is accepted convention in the industry that you DO NOT.
I have pasted below MCA Brown Book Code for work boats extract, found here http://www.dft.gov.uk/mca/brown-withpage8.pdf
It mentions an overload alarm which I can also say I have never come across. This of course would be no good during a short circuit.
The safety of the vessel can not be compromised by fitting a device that may fail just when you need it.
The Brown book is not the only code out there, there are many and non expect a fuse. There maybe exceptions to this, but I have yet to see one.
8.2.5 All circuits, except the main supply from the battery to the starter motor and
electrically driven steering motors, should be provided with electrical protection
against overload and short circuit, (i.e. fuses or circuit breakers should be
installed). Short circuit protection should be for not less than twice the total rated
current of the motors in the circuit protected.
Steering motors should have an overload alarm in lieu of overload protection.
Thanks
I have just found this conversation after joining today.
I work in the commercial boat sector and have worked in the leisure sector too, for many years.
I have never seen a engine starter motor protected by a fuse or circuit breaker, NEVER. It is accepted convention in the industry that you DO NOT.
I have pasted below MCA Brown Book Code for work boats extract, found here http://www.dft.gov.uk/mca/brown-withpage8.pdf
It mentions an overload alarm which I can also say I have never come across. This of course would be no good during a short circuit.
The safety of the vessel can not be compromised by fitting a device that may fail just when you need it.
The Brown book is not the only code out there, there are many and non expect a fuse. There maybe exceptions to this, but I have yet to see one.
8.2.5 All circuits, except the main supply from the battery to the starter motor and
electrically driven steering motors, should be provided with electrical protection
against overload and short circuit, (i.e. fuses or circuit breakers should be
installed). Short circuit protection should be for not less than twice the total rated
current of the motors in the circuit protected.
Steering motors should have an overload alarm in lieu of overload protection.
Thanks
SimonPembs
New member
Starter Motor Fuse
Here is ISO (EN ISO 10133:2000) standards take:
8 Overcurrent protection
8.1 A manually reset trip-free circuit-breaker, or a fuse, shall be installed within 200 mm of the source of power
for each circuit or conductor of the system or, if impractical, each conductor shall be contained within a protective
covering, such as a sheathing conduit or cable trunking, for its entire length from the source of power to the circuitbreaker
or fuse.
The following constitute exceptions.
a) The main power-feed circuit from the battery to an engine-cranking motor, if sheathed or supported to protect
against abrasion and contact with conductive surfaces. See 7.2.
Find this standard here:
http://ec.europa.eu/enterprise/poli...sed-standards/recreational-craft/index_en.htm
Here is ISO (EN ISO 10133:2000) standards take:
8 Overcurrent protection
8.1 A manually reset trip-free circuit-breaker, or a fuse, shall be installed within 200 mm of the source of power
for each circuit or conductor of the system or, if impractical, each conductor shall be contained within a protective
covering, such as a sheathing conduit or cable trunking, for its entire length from the source of power to the circuitbreaker
or fuse.
The following constitute exceptions.
a) The main power-feed circuit from the battery to an engine-cranking motor, if sheathed or supported to protect
against abrasion and contact with conductive surfaces. See 7.2.
Find this standard here:
http://ec.europa.eu/enterprise/poli...sed-standards/recreational-craft/index_en.htm