Fuses

[Phil HadnuttParticipant @philhadnutt]

Hi

do you guys use Fuses in your boats if so any ideas how and where to buy the bits thanks

phil

[Phil HadnuttParticipant @philhadnutt]

Equipment

[Charles OatesParticipant @charlesoates31738]

A fuse is an insurance policy but not everyone fits them. Generally, the less someone knows about electrics the more important it is to fit one, because there a higher risk of making a mistake..

The simplest way to fit them is to buy spade fuses from Halfords, or a similar shop. Then cut a power wire and fit spade connectors to each end and the fuse will just plug in.to the connectors.

If you type 'fuses' into the forum search box you'll find a lot more discussion about them.

Charles.

 

Edited By Charles Oates on 12/11/2022 15:29:17

[Chris EParticipant @chrise]

Yes, yes & yes again!

I might overdo it but I put one between the battery and anything else & then another between the esc and the motor. I use the blade fuses that can be obtained from any car accessory shop and a couple of spade connectors – one onto each fuse leg. Cheap easy to buy & work just fine.

You can go way upmarket and perhaps you need to do so if you have a very high power installation but for me the blade fuses are perfect.

Example fuses

Example Spade Connector

Edited By Chris E on 12/11/2022 15:35:35

[The Long BuildParticipant @thelongbuild]

Component Shop do one as well.

Fuses

[Richard SimpsonParticipant @richardsimpson88330]

In any electrical installation, domestic, industrial, plant, vehicles, ships, etc…etc… fuses or circuit breakers are there primarily to protect the wiring then secondarily to protect the components. In most circuits the wiring is inaccessible, which is not quite such an issue for model boats however the result of overload on wiring is excessive heat, which is obviously to be avoided at all costs.

While we may know exactly what we are doing as regards sizing components and wire capacities what the fuse does for us in our model boats is prevent overheating of the wires in the event of overload. Overload could occur for any one of a number of reasons such as the shaft seizing or coupling failure but the most likely cause is something fouling the propeller, such as weed or plastic debris in the water. Any of these things can cause higher than normal loads in the components to the point of serious overload and consequently overheating. This can lead to insulation failure and potential short circuits and ultimately fire. The fuse is designed to rupture before temperatures in the wiring become excessive, which is why, when choosing the fuse size to use the current carrying capacity of the wiring is just as much a consideration as the components.

The bottom line is that you should always fit a fuse to protect your boat from any issue that may lead to abnormally high current. The most common location is in the positive wire from the battery to the speed controller, which would also protect against a short in the battery.

As regards sources, model electrical suppliers such as Component Shop will have what you need.

[Richard SimpsonParticipant @richardsimpson88330]

Sorry Larry, posts crossed!

[Colin BishopModerator @colinbishop34627]

I am also a fan of fuses on the belt and braces principle. They cost peanuts to fit but can save you a lot of money if something gets jammed down the line.

A fuse next to the main battery will protect the whole system and as Chris says, another between the motor and speed controller can protect the final drive.

Colin

[Dave Cooper 6Participant @davecooper6]

Yes, fit a fuse as per previous posts. The question often arises "what size" (fuse rating). This will be in AMPS or, electrical current. Firstly, you'll need to measure how much your motor is drawing under load…..not easy, so this will probably have to be an estimate with the boat in some water…

You can use an ammeter, multi-meter or watt meter. (For, the watt meter you'll need to convert from watts to amps). You can always start with small fuses (from the low end of the estimate) and move up in steps until you find one that doesn't blow. Sounds crude but it does work. I use a calculation method and then add a percentage safety factor (say 50%).

I also do some tests on the bench first to give a useful starting point.

Good luck.

Dave

[Colin BishopModerator @colinbishop34627]

When you buy a motor the specs often state the stall current, that is the maximum curent the motor will draw if physically stopped from rotating such as when a propeller gets jammed for example.

The stall current will be well in access of the normal loaded current (which may also be stated) so you can set your fuse value to a level below the stall current and slightly above the maximum efficiency draw at 6/12v.

We did discuss a lot of this a couple of years ago (maybe old age is catching up with us!)

**LINK**

Colin

[Chris EParticipant @chrise]

Stall current is voltage specific so be aware when reading manufacturers specs.

[Kev.WParticipant @kev-w]

Had 2 boats fitted with fuses, was told this was needed to protect my ESC / Battery.

Boats kept stopping & had to be rescued, spoiled my days sailing, so after 2 or 3 fails, I removed the fuses, not had a boat die in the water since.

The fuse is designed to be the "weakest link", but if your system is robust enough, the last thing you need, is a weak link, it will always spoil your day.

Don't use fuses anymore, not had a failure since deleting them from my boats.

 

Edited By Kev.W on 13/11/2022 16:03:13

[John W EParticipant @johnwe]

So, you wish to run the risk of NOT FITTING A FUSE? – This is a result of not fitting a fuse and this happened to me on the test bench – on an Ebay special speed controller – all the way from Ongy Pongy good job it was on the bench and not in the middle of the lake.

I fit fuses as everyone else – between the battery and the speed controller and I tend to use the automotive blade type fuses.

John

[Colin BishopModerator @colinbishop34627]

If your fuses kept failing Kev then the problem was that they were too low a rating.

A fuse has no downside really, in normal circumstances it is just part of the wiring and will only fail if the wiring or one of the components aboard becomes overloaded or develops a short circuit.

Speed controllers contain a number of components and have an open circuit to the battery when the model is switched on. If one of the power handling components fails then the battery could go short circuit and dump a large amperage through the wiring which can ruin the battery, melt the wiring and quite likely cause a fire, just like in John's photo. It can and does happen.

Likewise, if a motor stalls due to a jammed prop or something breaks in the driveline then, unless the speed controller has its own fuse or internal power breaker, the motor will fry.

Your house supply is protected by RCDs to cope with short circuits – you wouldn't remove them would you?

Fuses are very cheap and effective insurance. If correctly rated they will be effectively invisible. In the event that you do need them it could save you a lot of money and even a lost boat given the high discharge rates even model batteries are capable of.

Colin

[Richard SimpsonParticipant @richardsimpson88330]

I think to be fair Kev that the 'weakest link' does not necessarily mean a 'weak' link. It is designed specifically to be the point of failure in the case of an overload, thereby protecting everything else. It should be sized to operate continuously and reliably under normal operating currents. If the fuse is failing under normal operating conditions then, as Colin says, either the fuse is incorrectly rated or there is something wrong with them. I have equally had fuses fitted to my boats and never had one blow in as many years as I care to remember.

It is nothing more than an insurance against something going wrong. You can argue that a perfectly set up model that is correctly maintained and serviced should never fail, which is perfectly true. The fuse is not only there for that though, it is insurance against that bit of weed, fishing line, plastic bag or whatever you might pick up that gets caught round the prop. And before anyone says I shut the throttle off before anything can happen, invariably it won't lock up and stop the boat dead, it will increase the load on the motor enough to make you wonder why it looks like it has slowed down a little and while you bring it into the bank it will die because the high current has just blown the speed controller.

To me its a bit like saying "I don't bother with pet insurance because my dog's never been ill".

[Ray Wood 3Participant @raywood3]

Hi All,

I can only speak from personnel experience on this, I have built 25 electric boats built over the last 6 years, no fuses fitted never had a problem !! So I'm with Kev on this one

I only use Mtronics speed controllers, my cat insurance cost's the same as one a month

Would seem a good idea if you can be bothered

Regards Ray

[Colin BishopModerator @colinbishop34627]

Paul Freshney never fitted fuses either – we agreed to disagree! My Dad worked in the electricity supply industry and taught me good practice.

You must love your Moggy Ray, at that price I'd be having kittens…

Colin

[Charles OatesParticipant @charlesoates31738]

To be fair to Kev, he made a point of saying 'if your system is robust enough'. I bet that doesn't include the often suspect far eastern speed controllers with ridiculous specifications. The late great Dave Milbourn often didn't bother with fuses either, but he knew his stuff better than almost anyone. Me? Some boats have a fuse, and always in a lipo powered model, seldom in other more sedate models. A lifetime of models,lets me know when I should fit one. My only advice is that anyone who needs to ask about them should always fit one, there's not enough knowledge there to take a risk.

Charles.

[Chris FellowsParticipant @chrisfellows72943]

Yes, I remember Dave saying in one of his posts that he didn't fit fuses. The Huntress I bought off him doesn't have one.

I will only be fitting good quality components in my builds but will give fuses some thought.

Chris

[Colin BishopModerator @colinbishop34627]

I never realised we had so many Refuseniks on the forum!

In the end, it's whatever floats your boat. I prefer the peace of mind but then I am a cautious person and listened to my Dad. Richard is a professional engineer.

Granted a short circuit causing a burnout is not all that common, but when it does happen it can be quite expensive and a replacement fuse is cheaper than a new speed controller or motor. I've seen or heard of it happening on a number of occasions.

Yes, Dave Milbourn didn't fit fuses but when he was running ACTion Electronics he was quite happy to sell fuse and power distribution boards and fully recognised the potential risks! You can still buy them.

**LINK**

Colin

[Charles OatesParticipant @charlesoates31738]

Not refuseniks Colin, just differences in use and application. To expand a bit, a fuse is at its best in a constant current system, less so in a circuit repeatedly changing polarity and load. If I have a model where the burst current is repeatedly higher than the safe constant maximum the fuse is rated at I'd try and get a slow blow fuse or not use one. The escs I use are happy with a burst current higher than the constant current, so it's not a problem for them.

When Kev said he kept having fuses blow, and I'm quite sure he's well able to work out the best value, I wondered if a high burst current was the reason.

It all depends on the model and equipment used, and electrical loads they're subjected to.

Re Dave selling fuse boards etc, of course we sold them, he was in business, and his customers weren't as smart as him about electrics.

[Colin BishopModerator @colinbishop34627]

I've actually got one of the ACTion fuse boards! It's not in a boat yet though.

Colin

[ashley needhamParticipant @ashleyneedham69188]

Usually I find myself soldering on a Deans connector to virtually all the ESCs I buy, it is very easy to fit female blade connectors and an extra short bit of wire while you are about it.

So saying, probably only half my boats have fuses, mostly the newer ones with Lipo s.

Ashley

[Richard SimpsonParticipant @richardsimpson88330]

Posted by Charles Oates on 14/11/2022 10:45:17:

Not refuseniks Colin, just differences in use and application. To expand a bit, a fuse is at its best in a constant current system, less so in a circuit repeatedly changing polarity and load. If I have a model where the burst current is repeatedly higher than the safe constant maximum the fuse is rated at I'd try and get a slow blow fuse or not use one. The escs I use are happy with a burst current higher than the constant current, so it's not a problem for them.

When Kev said he kept having fuses blow, and I'm quite sure he's well able to work out the best value, I wondered if a high burst current was the reason.

It all depends on the model and equipment used, and electrical loads they're subjected to.

Re Dave selling fuse boards etc, of course we sold them, he was in business, and his customers weren't as smart as him about electrics.

Just goes to show we are learning all the time. 40 years at sea and a qualification in Marine Electrical Engineering and I never knew that polarity changes had any effect on a fuse. Surely though when the fuse is fitted between the battery and the ESC the polarity doesn't change?

[Colin BishopModerator @colinbishop34627]

As Richard says, the polarity at the battery end can't change! Only that between the ESC and the motor and I dobt if that would affect a fuse wire in normal circumstances. Obviously when a motor starts there is a momentary peak but that should normally be within stall current limits. Correctly rated fuses should be able to pass working currents in all normal situations in both directions (it is only a wire after all!) and only break if a short circuit or motor stall current occurs. I have always fitted fuses and they have only blown if I have inadvertently caused a short circuit. Basically, shortcircuits, however caused, are what I am aiming to protect from and so far so good but each to their own and you take the risk as you wish.

Colin

Edited By Colin Bishop on 14/11/2022 20:29:31

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