Model Boat Mayhem

Technical, Techniques, Hints, and Tips => Batteries & Chargers => Topic started by: Nordlys on September 05, 2014, 09:08:55 PM

Title: Battery cells getting hot
Post by: Nordlys on September 05, 2014, 09:08:55 PM
I've recently noticed that two cells on my 9.6v Nimh pack are getting quite
hot after 20mins or so out on the water in my twin prop model.

I am having some trouble with the prop tubes getting very hot but this, I think
may be due to a slight misalignment of the couplings (they are not the Huco type
but have a rubber centre piece joining the two alum coupling pieces)
Model boatbits sell them.

Its the battery warming up that puzzles me -anyone any idea how this could happen please?
Nordlys.
Title: Re: Battery cells getting hot
Post by: Tug-Kenny on September 05, 2014, 10:28:07 PM

It sounds like an overload.  Have you checked the free rotation of the prop shaft when disconnected from the motor.

For the battery to get hot it must be excess current being taken.

Cheers

ken
Title: Re: Battery cells getting hot
Post by: Leaky Bottom on September 06, 2014, 07:44:58 AM
If it's only two cells in the pack that are getting hot then the internal resistance of those two cells has increased and causing a heat build up, so I would say the pack is nearing the end of it's life
Title: Re: Battery cells getting hot
Post by: boatmadman on September 06, 2014, 08:27:48 AM
I would agree that the battery is on its way out.


Regarding the shaft running hot, have you stripped out the shaft and cleaned it? A good scrub with scotchbrite often helps, finished with a smear of oil on re assembly.


Ian
Title: Re: Battery cells getting hot
Post by: Nordlys on September 06, 2014, 08:34:24 AM
Yes, the shaft does rotate quite freely (both tube and shaft are new) when disconnected from coupling.
I thought there was a slight misalignment which may be causing the shaft to rotate tighter on the bearing than normal, hard to say. I am about to change the coupling today.

The battery may well have a fault I suppose - all a bit trial and error?
The print on the two cells in question has faded with the heat!

Blew a 25a fuse last week out on the lake which may be due to the shaft alignment.
I am running with two 600 Mtroniks Vision motors, 6-12v, with one 25a Esc.
N
Title: Re: Battery cells getting hot
Post by: Tug-Kenny on September 06, 2014, 10:16:19 AM

You don't say the amperage of the battery.
 
I bench tested my 600 and found it can take over 12 amps when under load  ??


ken

Title: Re: Battery cells getting hot
Post by: Nordlys on September 06, 2014, 10:33:35 AM
The battery rating is 4600mAh - 8 cells at 1.2v. VP Racing battery written on side.

I did pack grease into the tube, most of it comes out of course once you fit the shaft.
N
Title: Re: Battery cells getting hot
Post by: boatmadman on September 06, 2014, 11:16:18 AM
Best not to pack the tube with grease, it causes drag and increases load. All you need is a smear at each bush. Use water proof grease.
Title: Re: Battery cells getting hot
Post by: malcolmfrary on September 10, 2014, 10:14:02 AM
If an entire battery gets warm, or even hot, it is a sign that it has been working hard. Probably not particularly harmful in itself. If one or two cells get hot, they are the weak link, and are not as good as their companions.  Unless you can replace individual cells with others to match the remainder, the pack is on its way out.
Title: Re: Battery cells getting hot
Post by: Nordlys on September 10, 2014, 11:55:14 AM
Thanks for that summary Malcolm.
Just two cells are warming up when running AND when charging.
Ran a different pack today - altogether different.
Actually the suspect pack is not that old ie less than 2yrs.
Bit disappointing considering it was quite an expensive one from Component shop.
N
Title: Re: Battery cells getting hot
Post by: NFMike on September 10, 2014, 12:50:57 PM
Battery lives seem to be extraordinarily variable. I think there are two major issues that play.

One is the quality of manufacture. Tricky one as there aren't actually a lot of battery manufacturers so a lot of badge engineering occurs. You might be safer with a 'known' make, but then again it's not a certainty.

The other issue is how the battery is treated. Most cells can be damaged by shock, so if posted to you and not very well packed they could be damaged before you get them. Obviously if you drop them, etc, yourself you can damage them.
The other treatment issue is charge and discharge. If mishandled electrically - overcharge, over-discharge, shorts, too high rates of charge/discharge, and/or the battery getting too hot during any of those (eg. when charged in situ) - then the battery, or some cells within, can be damaged.

I have a Braun battery shaver with a NiCd which has been going for donkey's years and is still fine. But it has a dedicated charger, is obviously only discharged at it's designed rate and doesn't sit unused for months at a time. Unfortunately not many of our models have the same predictable and well controlled environment, so a higher early death rate is almost inevitable.
Title: Re: Battery cells getting hot
Post by: Nordlys on September 10, 2014, 01:03:45 PM
The battery had been performing ok up until a few months back. I think I
noticed a drop off in length of time my boat was running on this battery
followed by a lack of speed of the boat too- on a full charge.

I didn't take a lot of notice until last week when a fuse blew (25A)
not that that had any particular connection that I could think of!

But because of the battery cell(s) temp it made me ask the question.
9.6v 4600maH can be quite expensive!
Running on 8.4v today and quite adequate.
N
Title: Re: Battery cells getting hot
Post by: RongTick on February 07, 2015, 09:53:31 AM
which brand of the battery do you use ?
Title: Re: Battery cells getting hot
Post by: tigertiger on February 07, 2015, 10:57:09 AM
Just a thought.

If the shaft is hot, suggests friction, maybe leading to increased load on motor and battery, and subsequent battery heat.
Changing coupling may also fix battery heat issue. Or maybe not.
Title: Re: Battery cells getting hot
Post by: roycv on February 07, 2015, 11:28:03 AM
Hi on the battery points. About a year or so ago I asked fellow club members if they had any duff batteries and I received a half dozen 6 cell batteries.
From these I isolated the duff individual cells, re-soldered the packs  and now have 3 sets of 7.2 volt and one 6 volt and one 4.8 volt  batteries, not quite up to the original full spec but I only have low current applications so no problem.

All good stuff from above contributors so consider removing 2 duff cells and you have a good 6 cell pack.

You could also contact the suppliers and ask for suggestions?  They might put 2 new cells in at a cost, you never know!
regards Roy
Title: Re: Battery cells getting hot
Post by: RAAArtyGunner on February 07, 2015, 10:37:42 PM
Roy,

Just about everyone says to not solder packs but spot weld???? to eliminate heat easier said than done.

Have often considered what you have done, ie salvage packs and repair, particularly for power tools, what size iron did you use.
Title: Re: Battery cells getting hot
Post by: mermod on February 08, 2015, 04:22:28 AM
I may have missed it but have you checked the back and forward play in the shaft with the uni in place? unless your uni is phenomenally out of alignment it shouldn't cause heat but if the uni is pushed hard enough against the front bushing/bearing it will heat up real quck, I usually aim for 1/2 mm play.
Obviously this relates to the shaft heat not the batteries :)

Phill
Title: Re: Battery cells getting hot
Post by: roycv on February 08, 2015, 09:45:52 AM
Hi RAAArty...I have been salvaging packs for years now.  I use a 100+ watt iron and solder very quickly and cool with wet tissue after.  Spot welding is best but as I can't do it is not an option.
As you are salvaging packs you are not dealing with top performance cells so think of it as a bit of green re-cycling.  I only have low curent use anyway.
My current 32 inch cargo boat runs all afternoon on a 2 Ah pack!  I also have one of those current charge monitors, very good for sorting out cells with a 'declined ' Ah capacity.
regards Roy
Title: Re: Battery cells getting hot
Post by: RAAArtyGunner on February 08, 2015, 11:00:23 AM
Roy,
 Thank you will have to get a bigger iron as spot welding is also out of the question for me. :-)) :-))