(Not so) simple?

[Scuba Steve]

I have what I would assume is a simple problem, but it is proving quite the opposite for me!

I recently got a Scubapro Sea Glider. This is a diver propulsion vehicle. It is used to pull divers through the water faster than they could swim. The item is not sold/produced in the U.S. any longer and I have been having considerable difficulty finding any kind of technical manuals or schematics.

The circuit is pretty simple. It consists of a 12v 26a dc sealed lead acid battery for power, a switch, and a dc motor with a propeller attached. There is a diode connected to the terminal block of the motor with the cathode on the positive terminal and the anode on the negative terminal.

The problem I am having is overheating of the conductors at the terminal block. I used the Sea Glider on a dive today and it just stopped working in the middle of the dive. When I took it apart, I saw that the wire's insulation at the terminal block got so hot that they melted together and melted the terminal block.
Since I got this item used, I am wondering if perhaps the wrong diode has been installed and is causing too much resistance (heat). Is the diode even necessary? What is the diode's function in the circuit?

Thank you in advance for any assistance!

 

[Leftyretro]

I have what I would assume is a simple problem, but it is proving quite the opposite for me!

I recently got a Scubapro Sea Glider. This is a diver propulsion vehicle. It is used to pull divers through the water faster than they could swim. The item is not sold/produced in the U.S. any longer and I have been having considerable difficulty finding any kind of technical manuals or schematics.

The circuit is pretty simple. It consists of a 12v 26a dc sealed lead acid battery for power, a switch, and a dc motor with a propeller attached. There is a diode connected to the terminal block of the motor with the cathode on the positive terminal and the anode on the negative terminal.

The problem I am having is overheating of the conductors at the terminal block. I used the Sea Glider on a dive today and it just stopped working in the middle of the dive. When I took it apart, I saw that the wire's insulation at the terminal block got so hot that they melted together and melted the terminal block.
Since I got this item used, I am wondering if perhaps the wrong diode has been installed and is causing too much resistance (heat). Is the diode even necessary? What is the diode's function in the circuit?

Thank you in advance for any assistance!

Not sure what the purpose of the diode is for that application. It is wired such that it is normally reversed biased so it's not conducting and shouldn't be a problem. However if the diode failed and shorted cathode to anode that would of course cause a direct short circuit for the battery and melt the wires. So I would remove and test the diode, replace all wiring, recharge/test the battery and test the motor. You really should have some kind of fuse or circuit breaker in series with the battery. I wouldn't bother replacing the diode if it's bad.

Good luck

PS: Take Pommie advice on protecting the switch contacts and replace the diode if bad.

 

[Pommie]

The diode is to prevent arcing at the switch. The heat will be caused by a bad connection. Cleaning it may be all that is required. Can you post a picture of the connection?

Mike.

 

[Scuba Steve]

Thanks for your quick responses Mike and leftyretro.
Here is a pic of the terminal block and the wires that were attached. I had to take it apart to get it out of the bulkhead. The wire terminals were held down by two small nuts. The connections were tight when I took them off.
The crescent wrench is just there to hold the terminal block. You can see where the insulation on the wires is burned and also the plastic insulation of the terminal block itself.
I was thinking of switching to a terminal block with set screws so I can do away with the wire terminals. What do you think?

Thanks again!

**broken link removed**

 

[RadioRon]

It appears that the hottest spot was right where the red wire lug touches the stud in the terminal block. I don't see any evidence of overheating of the diode body or on the diode wire. I also don't see very much heating of the black wire. In fact, the heat appears to have been concentrated only at the red wire connection point on the stud. This seems to have heated the stud up and melted the plastic around the stud. This seems like a classic case of too much resistance right at the point where the wire lug should touch the stud and stud nut. Obviously a lot of current is flowing in this connection. Something about that connection was not good. When such connections carry a lot of current, the metals have to be extremely clean and bright with no oxidation before they are tightened together. Scrubbing each metal surface to expose bare metal is often done in automotive connections and this is similar. A bad (resistive) connection could be the whole problem here. It might be wise to use an electrically conductive paste around the connection.

edit: it could be that the heat is being generated on the other side of the stud. What does it look like behind there?

 

[Scuba Steve]

I think you are right on the money RadioRon. The connection on the back of the terminal block isn't anywhere near as bad as on the front. It is obvious that this terminal block in now junk. Since it is an OEM part (and these things are out of production) , I will have to replace it with something else. I was thinking a set-screw type of terminal would work well.

 

[eblc1388]

I was thinking a set-screw type of terminal would work well.

You'll need to solder up the individual copper strands before they can make a good connection with set screws. Alternately there is bootlace ferrules (i.e. thin metal tubing) to place onto the stripped end of the wire so the force of the set screw is onto the metal tube instead.

 

[JimB]

You'll need to solder up the individual copper strands before they can make a good connection with set screws. Alternately there is bootlace ferrules (i.e. thin metal tubing) to place onto the stripped end of the wire so the force of the set screw is onto the metal tube instead.

Ferrules and crimps OK, but soldered multistrand wire in a compression type terminal? NO WAY!

Depending on the type of terminal, the screw will just cut straight through the soldered wires, or if a good connection is made, the solder will "creep" over time and the connection will become loose.

If you are putting a multistrand wire into a compression terminal, twist the strands together (no too tightly), insert wire in terminal and tighten the screw.

Solder? been there, done that and regretted it a couple of months later.

JimB

 

[RBeddow]

Hey Steve,
I just got one of the ScubaPro Sea Glider too and having the same issue trying to find information on it. I was curious to see if you ended up finding an online manual or just a good site to refer to about it. My dad gave it to me, I just bought a battery for it, but there is a lot of corrosion on the battery connector so I'm pretty sure I might need to buy a new one.

I would really like to hear what you think about it after you have it up and going now... Does it work well? Are you having any other issues? Is it dependable?

Rick

 

[KeepItSimpleStupid]

I don;t like those connections period. For, one solid wires, should not be crimped. Even so, some sort of compound needs to be used under the connections, There is also way to many different materials there that can create little "batteries" when a tiny bit of electrolyte shows up.

The diode is there to protect the switch which was said earlier.

Aside from the obvious poor choice of connection method and even non-tin plated wire, one should look at the actual motor current. worn brushes could be another thing to look at. I've been successful going to the hardware store or a vacuum cleaner repair place and getting brushes and either filing them to size or making the holder smaller. I did that to a car heater motor.

If you had the room, I might think about adding a operating hour meter and doing preventative maintenence.

What comes to mind is actualy re-wiring the thing. Use the proper anti-corrosion paste and maybe even using adhesive lined heat shrink.

The only way, you can attach a diode like that is to crimp, solder, clean the flux and cover with adhesive lined shrink tubing, You can even buy crimp connectors that have the adhesive lined shrink.

I might consider a stainless bolt and a stainless bellville washer with anti-corrosion paste. The stud would not be conducting current anyway.

 

[audioguru]

I think the crimp of the terminal on the red wire is not tight enough, or maybe the red wire strands or the inside of the crimp part were corroded a little before they were crimped.
I had some small low current brushed motors get so hot that they melted their nylon holder. The commutator was worn out and was shorted together by the brushes.