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Author Topic: How "fused" am I?  (Read 4242 times)

sunnybob

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How "fused" am I?
« on: February 18, 2008, 08:21:59 PM »

I have finally started to put together the electronics on my cruiser, and my single sheet of instructions just dont cut the mustard (nothing unusual there  >>:-()

I have 2 x electronize 545/12 motors, controlled by a single elctronize FR30HX esc.The diagram shows a fuse between the battery and motor, but nothing as useful as a value by the side of it ::) ::)

Suggestions please?? :) :)

Also, while youre here, I have 2 x JP energ 6.0volt motor batteries. Can I rig them up in parallel to give me more run time? or will that overload the system with too many amps?

All help gratefully received :D :D
Bob
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boatmadman

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Re: How "fused" am I?
« Reply #1 on: February 18, 2008, 08:40:10 PM »

Hi,
The fuse size to fit should be no greater than the max continuous current rating of the esc - if you have any doubt about what that is or should be, contact electronize, they will tell you.

As for the batteries, assuming they are gel cells, yes you can rig in parallel without risk, that will give double the run time of a single battery.

The amps pulled in the system is dependant on the type of motor and size of prop, so parallel connection of batteries has no influence on this.

I recommend connect up one motor/prop to the battery - exclude the esc at this time, and measure the amps drawn by connecting an ammeter between the motor and battery. Do this with both motor/prop drive lines. This will give you the total max running current of the set up.

As an aside, I have fitted fuses between the motor and esc on a twin motor setup - ie. 20amp esc feeding 2 motors, each motor has a 10a fuse between it and the esc. This means the esc cannot be overloaded and, if one prop gets fouled up and stalls a motor thus blowing the fuse, there is a good chance the other motor will get the boat back to shore.

Hope this helps

Ian
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sunnybob

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Re: How "fused" am I?
« Reply #2 on: February 18, 2008, 09:13:20 PM »

Ian, your post has answered some, but raised other questions.
My digram from electronize, shows the (single) fuse between the battery and the esc.
But i like your idea better, as hopefully one of the motors will still run if a fuse blows.
But whats the likelihood of a short between battery and esc.

I know that each fuse adds load to the circuit, would it be "overkill" to have a bigger fuse between battery and esc as well as the 2 smaller ones?

The esc handles 30 amps, so logically, I should have a 30 amp before the esc, and a 15 amp on each motor?

The motor batteries do not have any amperage on them, but they are NiMH, is that the same as "gel"?
The actual label reads 6.0volt SC-3300H FLAT. Any idea what that translates as?

The electronics wiring isnt finsished yet, so at the moment I cant try a motor. But I do have the meter and ability to find out the current draw.
Thnaks
Bob
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Colin Bishop

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Re: How "fused" am I?
« Reply #3 on: February 18, 2008, 09:37:45 PM »

Fuses don't load the circuit, they are just a thin bit of wire that will "blow" if the current exceeds a certain level.

NiMH batteries are Nickel Metal Hydride. "Gel" cells are lead acid and not the same at all. The main difference is that the charging regimes are different. Plenty of info available if you just Google!

NiMH batteries should normally state their amp hour capacity Not sure exactly what your label means but it suggests that the capacity is 3.3 amp hours (3300 milli amp hours). The quoted voltage of 6v suggestes that there are 5 cells as each NiMH cell has a nominal voltage of 1.2v.
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boatmadman

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Re: How "fused" am I?
« Reply #4 on: February 18, 2008, 09:48:14 PM »

Using my suggestion of fuse after esc, the battery connects straight to the esc, so there is no way a 'short' can take place, unless of course the positive and negative leads come into contact - and we all know not to allow that.

You really only need to fuse one side of the esc - either twix battery and esc, or esc to motor. There is nothing to gain by fusing both sides as the 15a fuse between esc and motor will always pop before the larger between battery and esc.

As for the Nimh batteries - I stand to be corrected here, but it is my understanding that you have to be very careful connecting these in parallel, because if they are not balanced electrically, there is potential for one battery to feed another with potential overheating and exploding issues!

Incidentally, I blew up a Nimh pack accidentally by overcharing, it was a AAA PACK.Two of the cells disintegrated completely and there was powder everywhere!
So, the moral is - be careful, there is a lot of energy in those little batteries.

Ian
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sunnybob

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Re: How "fused" am I?
« Reply #5 on: February 18, 2008, 09:50:58 PM »

colin, absolutely right, there are 5 cells in each battery.

So does my original plan of 2 of them in parallel cause any problems?
If they are only 3.3 amp each, then the 30 amp controller wont be bothered.

Now I'm wondering if I should get more batteries? I have no idea how long the motors will work on those sizes. I can see me having a bordom threshold of around a hlaf hour. will the boat last that long?
 O0 O0 O0
Bob
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sunnybob

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Re: How "fused" am I?
« Reply #6 on: February 18, 2008, 09:55:03 PM »

Ian, how do I balance these batteries? can I charge them in parallel? Or do I need a diode in each line to stop back emf?

Once again, the deep end is where I appear to have settled into, without bothering about the shallows ??? ???
OK, youve saved me one fuse  O0 the search for the pefect system continues ;D
Bob
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boatmadman

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Re: How "fused" am I?
« Reply #7 on: February 18, 2008, 09:55:32 PM »

Bob,

The rating of the batteries at 3.3a indicates that they will supply 3.3a continuously for 60 mins, or for example, 33a for 6 mins!!!! or 66a for 3 mins!

So, you need to think in terms of amp/hours, hence when a battery is specified as, say, 3.3ah. or 3300mah (these are both the same rating).

So, as you can see, the esc can be overlaoded by these batteries, but, as I said before, the load depends on how much work the motor has to do to turn the prop and drive the boat.

Ian
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boatmadman

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Re: How "fused" am I?
« Reply #8 on: February 18, 2008, 10:00:47 PM »

Again, I stand to be corrected, but I understand that for these batteries, you need to match the individual cells inside the battery at the time of making up the pack.

For your application, I suggest you think about using one battery at a time, bring the boat in as it runs down and change the pack - or fit wiring and a changeover switch so you can swap batteries by flipping a switch over.

You should be aware that these batteries give full performance almost until flat, then drop off very quickly, not leaving you much to get back with if you are a long way out. You should experiment and get an idea of duration on the water.

Depending on the type of boat you are putting them in, it may be worth thinking of a gell cell (sealed lead/acid).

Ian
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sunnybob

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Re: How "fused" am I?
« Reply #9 on: February 18, 2008, 10:11:16 PM »

"xxxxx"! now I'm worried.
This old boat has bronze rods inside close fitting brass tubes for the props. There are no bearings, and there is a fair amount of resistance, even turning the props by hand.

I can see them causing a huge amperage to turn them properly.

I need to make a jury rig and see what these props pull from the battery before i commit any other resources.

Thanks Ian, even though youve given me more work, rather that than watching the boat catch fire on its maiden voyage.
bob
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boatmadman

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Re: How "fused" am I?
« Reply #10 on: February 18, 2008, 10:13:02 PM »

Good luck and keep us posted.

Ian
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Stavros

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Re: How "fused" am I?
« Reply #11 on: February 18, 2008, 10:58:41 PM »

Sunnybob if I was you I would take the shaft out and clean them up with 1000wet dry in case there is rust on then reassemble packing the shafts with grease spin then up just with the batt no esc and feel the shaft tubes to see if they are getting hot.If they are well as NASA would say HUSTON WE HAVE A PROBLEM but thats another story.

Stavros
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malcolmfrary

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Re: How "fused" am I?
« Reply #12 on: February 18, 2008, 11:17:01 PM »

Quote
But whats the likelihood of a short between battery and esc.
Very little likelihood of that, but a possibility of a problem inside the ESC.  The fuse between the battery and the ESC protects the rest of the boat from the possibility of an electrical fire.  As a previous poster has said, there is a lot of energy in those batteries, and you don't want it all let loose inside the ESC in a few destructive seconds.
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sunnybob

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Re: How "fused" am I?
« Reply #13 on: February 18, 2008, 11:24:10 PM »

Stavros, no rust on these babies, 50 year old bronze shafts. Must be worth more than the boat!!! But yes, I think houston should be put on defcon 3 {-) {-) {-)

mmmm. looks like I might as well use 3 fuses instead of two that was originally one. ::) ::)
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Stavros

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Re: How "fused" am I?
« Reply #14 on: February 18, 2008, 11:32:34 PM »

Posh shafts then but one question have you had them out and regreased them???????????????????????????????


Stavros
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Proteus

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Re: How "fused" am I?
« Reply #15 on: February 19, 2008, 12:10:49 AM »

sunnybob

I saw a post of your on another site I think , and you only have about i/2 a mill clearance iner to outer shaft so dont put grease in,

fredy
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FullLeatherJacket

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Re: How "fused" am I?
« Reply #16 on: February 19, 2008, 08:15:42 AM »

This might help you:
http://www.modelboatmayhem.co.uk/forum/index.php?topic=8674.msg84258#msg84258
PM me for any further info - I've got loads of it.
FLJ
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boatmadman

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Re: How "fused" am I?
« Reply #17 on: February 19, 2008, 08:20:41 AM »

As previously stated, there is a risk of a short in an esc, there is also a risk of an internal short developing in batteries. You cant get protect from internal battery shorts with a fuse.

The bottom line, I think, is that you have to determine what is an acceptable and reasonable risk compared with the cost required to minimise that risk.

I have never had an electronic failure or a disastrous short in over 10 years, but there is always the risk!

Ian
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Shipmate60

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Re: How "fused" am I?
« Reply #18 on: February 19, 2008, 04:53:43 PM »

Just a reminder of what can happen with an internal short in the ESC.
I recommend fuse between battery and ESC.

Bob
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boatmadman

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Re: How "fused" am I?
« Reply #19 on: February 19, 2008, 05:38:34 PM »

Very graphic, Bob.

Its got me thinking again, for the price of a fuse and holder............. :o
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sunnybob

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Re: How "fused" am I?
« Reply #20 on: February 19, 2008, 07:09:04 PM »

wow, so many replies,
so here are the answers to each of you.....

Stavros, yes i have greased them, thats the problem. This boat was built 50 years ago when R/C models needed a suitcase to carry the transmitter. Its all hand built, but is now not compatible with modern stuff. Those shafts were made for something like a half horsepower motor to work both through a hand built double splitter crown wheel gearbox. Theres no room for bearings, no room for seals, just no bloody room for anything  :'( :'( and these poofy little new motors are going to have earn their keep.


Proteus, yes, thats me, struggling to get this boat in the water without mortgaging my inheritance (hey, this boat IS my inheritance).

FLJ, they look terrific (shows what a sad person I am when I can get excited over a FUSE!!! {-)) but as already posted, total cost is number one issue with getting this boat going.

Boatmadman and shipmate 60, I'm convinced, If this boat were to catch fire for the sake of a fuse, my brother and sisters would hunt me down and drown me in a sack. :o :o

To all.... I've now tested the prop shafts, one is good, one makes a lot of bad noises. Obviously one of the shafts is bent and rubbing. It looks like I am going to have to find a way of fitting two new shafts through the hull . C.R.A.P.
Bob


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boatmadman

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Re: How "fused" am I?
« Reply #21 on: February 19, 2008, 07:16:27 PM »

Bob,

What is the inner diameter of the tubes, and the diameter of the shafts? Could you bush the tubes and run a smaller diameter shaft?

4mm diameter shafts are plenty strong enough for most applications.

Ian
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sunnybob

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Re: How "fused" am I?
« Reply #22 on: February 19, 2008, 07:31:48 PM »

No, the problem is in the tubes. because of the age of this stuff, its all home made. the tubes are just rolled brass, 1/4" outside diamter, and the shafts are a sliding fit inside them. I did grease the shafts, and the turning resistance was huge.

Theres not enough free tube at either end to start cutting or altering them. Theyre 14" long.

I think I'm going to have to buy new shafts, as I saw some at a model shop recently, and they had bearings and all manner of new fangled bells and whistles. Luckily, they are thicker rather than thinner, so I will just have to enlarge the holes through the hull,  But then I will have to work on brackets to hold them. SIGH.

I think I should have found this place and asked these questions BEFORE i talked my brother into parting with it. :'( :'(
Bob
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malcolmfrary

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Re: How "fused" am I?
« Reply #23 on: February 19, 2008, 11:42:04 PM »

If the tubes are a long way to being doomed, why not un-lube them, then "lube" with Brasso, and run them for a few minutes slowly.   They should show signs of freeing up, then when they sound a bit better, clean off the dead brasso, lube with oil, and try again.
Measuring the tube on my Graupner Lotse, the OD is 6mm, a bit smaller than most, and about the same as yours, but still with a 4mm shaft and bearing bushes.  A pair of Graupner shafts might do the job failing all else.
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Shipmate60

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Re: How "fused" am I?
« Reply #24 on: February 19, 2008, 11:50:34 PM »

If they are that large a diameter cant you fit a "modern" complete shaft inside the original tube.

Bob
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