Re: [Electric Boats] Minnkotas

battery management units would have prevented this. need to come up with a pc board to make them affordable. Because of their fragile nature lithium battery packs use bmu's. I think everyone could benefit.

 

 remember you are unique. Just like the rest of us.

---

From: Myles Twete <matwete@comcast.net>
To: electricboats@yahoogroups.com
Sent: Sunday, June 23, 2013 12:55 PM
Subject: RE: [Electric Boats] Minnkotas

 

"Double the power, yes, but it's my understanding that the HEAT comes from the AMPS (could be wrong)."

 

Almost…the heat is resistive power dissipation, which is proportional to AMPS SQUARED.

Double your amps, quadruple your power.

 

A lesson on heat and amps: Yesterday, I drove my 1920 Milburn Light Electric car to a friend's wedding.  A day earlier I picked the car up from storage and drove 25 miles to my home.  On arriving from my 1 ½ hour journey, I finger-checked the temperature of all the 28 battery posts and found 6 of them of concern (very hot).  Two pairs of these had battery interconnect cables that were also very hot, yet the connections were secure.  So I concluded that these cables themselves were defective and made a mental note to replace those 2 cables.  Wedding day arrives, I charge the car up, then assumed I'd be okay with the existing cables for the day---wrong!  Two-thirds the way up the hill to the wedding location, we smelled smoke, then almost just as we saw smoke, we heard a "pop" and the car came to a halt.  So, off to look for the source of the smoke.  A minute later it was clear: One of my battery terminals had 'melted' and left a pool of lead on the top of one of the 1yr old batteries.  Not coincidentally, this terminal was one of the 4 that I knew were at risk due to defective cables.  Now how much heat or power loss in that cable would it take to do this?  100watts? (no way).  500watts? (maybe) 1kw?  (sure).  How does it relate to resistance?  At the time of failure, the car's motor was probably drawing about 120amps.  Even 500watts of loss would imply a huge 4v drop across that cable!  This suggests about .034ohms of resistance.  Now, if the current were reduced merely from 120 to 80amps, the heat power would have been reduced to less than 50% of 500watts and may have saved the battery terminal.  Still, I consider this a lesson to be learned: Don't ignore high heat when you see it and don't delay in fixing the problem.  Also, while its seems like just a minor thing to see current increase from 70 to over 100amps, the power increase this represents is 2x and so every resistive element in that path will see power(heat) increase 2x for this mere 40% increase in current.  Pay attention to current.

 

-Myles

 

From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of stmbtwle
Sent: Sunday, June 23, 2013 9:47 AM
To: electricboats@yahoogroups.com
Subject: Re: [Electric Boats] Minnkotas

 

 

Double the power, yes, but it's my understanding that the HEAT comes from the AMPS (could be wrong). However considering the cost of the mods and the uncertainty of the outcome, it might be better to simply get a 24v unit. My canoe should fairly fly!

Willie

--- In electricboats@yahoogroups.com, "cire" <cirejay@...> wrote:
>
> You still will have doubled your power - watts.
>
> eric SV Meander
>
> --- In electricboats@yahoogroups.com, "stmbtwle" <stmbtwle@> wrote:
> >
> > Aye, there's the rub. Paddling a loaded canoe five miles against the tide is not my idea of fun; if it were I wouldn't bother with the motor!
> >
> > If I were to keep the total amps to no more than the motor was designed for (say with a circuit breaker) could I avoid this?
> >
> > Willie
> >
> > --- In electricboats@yahoogroups.com, George Schnellman <vectorges@> wrote:
> > >
> > > DC motors are very forgiving of the voltage supplied. at no-load the rpm
> > > will be directly proportional to the voltage., Double the voltage and you
> > > double the rpm. Triple the voltage and you triple the rpm. This holds right
> > > to the point 2 nanoseconds before the armature gets too hot and melts and
> > > the operator says, "Wow, I didn't see that coming".
> > >
> > > Be careful how much voltage you apply. Generally you will shorten the life
> > > of your equipment. It would not be fun to be an hour into a cruise and have
> > > the motor melt and have to paddle back.
> > >