Lights Out Part two

Mephisto26

Easier said than done man...

Mephisto26

Just to inform,

I gave the batteries to a friend this morning who is on the way to the states and he is going to send them to ISC. So hopefully like next week (or a month from now) I'm going to get news from them what they want to do in the matter...and of course I keep you guys posted about that...cross your fingers in any case...

In any case, it's a beautiful day here in Playa del Carmen, the sun is shining, it's warm already (08:20am) and I'm just packing to go cave diving...that just makes all the bad thoughts go away...

Cheers,
Patrick

Outlaw

Hey Patrick,

in order to claim the warranty you would have to have an "indepented" body who ISC will "recognize" stating that the fault did not come from your handdling. you realise that this is very very hard to happen.

i really do sympathize with you, honest. you are just one very unlucky meg diver...i dont know what else to say.

nice to see that you prepare for the worst and hope for the best...

Take care. hope you get a happy ending in the end.

Spyros

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Mephisto26

Here we go again...

So finally everything is said and done and soon hopefully I get my Head back...

So what happened in the mean time:

I ve sent them the battery pack that fried my electronics the first time (only the primary battery box and the electr.) which came from them and was wrongly poled. Back than I thought that they were lost in the trash but they reappeared in a strange coincidence...and so that time I spent 700 smth bucks on the repair...
Plus I ve sent them the two nimh packs I made which are rechargeable and where in the meg when the lights went out as explained before. Allthough they had the nimh packs before and told me that they are fine to use allthough not recommendet due to the voltage drop at the end...

Well the voltage drop didn't concern me that much since I regularly charged them and never experienced a problem...

Anyway long story short, they told me that allthough the nimh packs are good to use I may have used a wrong charger or smth like that and the output was too much and so the nimh pack in battery box 2 (secondary) fried the electronics. Is that possible by the way???
Anyway they said that this is why they do not recommend rechargeables...well this is kind of funny to me since the only reason I can recall from reading all the papers is that they don't recommend them due to the voltage drop...even when they inspected them they didn't warn me that this could happen...

But so it's my responsability and I need to pay...BUT...they do acknoledge that the other pack I ve sent them is from them and responsible for the first "frieing" and so I have the 700 smth bucks I paid back then as credit...and it covers pretty much this times repair...

So I'm almost/kind of ok/happy...

But still can anyone confirm/disconfirm the story of the charger mutating my batteries into electronic killers and/or show me where it says in any manual/hp that this can happen...???

Thanks in advance...

Anyway they also updated my Head to 2.06 for free and I will let you kow how that works...

Now I'm looking fwd to the 15th when I finnally get my head back (in dave I trust)

Warm 2008 regards,
Patrick

Skipbreather

Hi Patrick-

I am far, FAR from an expert on NiMH rechargeables, but I’ve played w/ them quite a bit both in building dive light battery packs and Rebreather packs as well. Using cheesy self built chargers I’ve seen over 30 v on a nominal 24 v Rebreather pack and close to 20 v on a nominal 14.4 volt dive light pack when fresh off the charger. I believe the literature calls this over voltage “surface charge” and if left unto themselves the packs will eventually calm down to several volts lower. If hooked up to a load the surface charge goes away quickly, but not instantly. My understanding is that my hot chargers shortened overall pack life. Quality “smart” chargers are both kinder to the pack’s overall life and do not have such a high over voltage when the pack shows ‘fully’ charged.

What nominal voltage were your packs? If memory serves, the APECS fry at anything much over a 9 volt primary (alkaline, lithium, etc) cell’s output.

Hope this helps. I have no doubt there are folks here on the board who know NiMH cells far better than I do.

Best,
Ken

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jradomski

I've also heard it referred to a "float" charge.. This usually happens when a charger only terminates by time or delta t change.. Pluggng in a nearlyy full pack that does not have the best temp sensing this can happen.. in most applications with the properly chosen pack voltage this should not be an issue.. usually you figure the max voltage of 1.6v per cell and calculate you pack size by that.. so a 5 cell pack should have a float voltage of about 8 volts-- even if you calculate it as 1.7 that will still only be 8.5v.. if you made a 6cell pack, it s definately a danger possibility.. the nominal voltage of a 5 cell nimh pack is 6.25v with a normal full charge volatge (for just a few minutes at most) of about 7.5v.. With the voltage range normally wanted on the meg NIMH cells are not the best choice.. a dual lithion ion or li polimer with a combined float voltage of 8.2V-8.4v (2 packs) is probably a much better choice as lion charges really dont want to charge above this voltage BUT the packs should be recharged around 7V (most will be permanently damaged around 5 v some even as low as about 6v)..

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snicks

From experience with RC-car races I find this problem with rechargeables, especially NiMHs not surprising (several smacked receivers along the way).

This "overload"-problem is present even if you use a $300+ charger with dU and dT (like I do). The problem lies in the charge characteristic of NiMH accumulators. While NiCd show a very pronounced drop in idle-voltage after a charging pulse when approaching full charge (pulse duration variing, typically 1-5 minutes) this drop is rather small in NiMHs. On some chargers the sensitivity of the dU criterion can therefore be adjusted.
If you made the packs yourself you probably didnt use matched cells (internal resistance and capacity). This is crucial during charging and when riding the pack down till its empty. During charging cell 1 (smallest capacity) is full and gives you a dU peak while the other cells are still properly charged. When the next cell is getting full ist also gives you a dU and so on. As a result the dU-peak of the whole pack ist "smeared-out" over a long time which makes it very difficult for the charger to determine when the pack is full (multi-cell chargers "know" how many cells are present and how big the dU peak should be). So you constantly overcharge the weakest cell, which is thereby damaged and will deteriorate the fastest... small step from there to death of pack. When this pack is being emptied, the weakest cell is empty while the others still have almost full voltage. As a result this cell will see a reverse polarity from the other cells, something that NiMH cells dont like very much. So this cell is damaged on this end as well. Because the dU-peak is "smeared-out" due to the individual cells getting full at different times the charger will overload the whole pack since no dU-peak is detected. If I remember correctly the float charge originates from oxygen bubbles forming on the electrodes inside the cell due to electrolysis when overcharging the cells (increasing cell resistance, thereby heating up the cell and giving internal cell overpressure). It is rather easily reversed by a 1-10 ohm high power resistor for about 5-10 secs (1-10 A peak ) or by resting the pack overnight. Reflex-chargers are said to avoid this problem, but I have fried several packs with one of those, so I cannot recommend it.

If you absolutely want to use rechargeables, I would advice to buy matched packs which are very common for RC-applications.

cya soon
Dirk

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steveharriss

Excellent comprehensive info...thanks