NiMh batteries question - use and charging....

Zerogee

Zerogee

Clencher's Bogleman
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I know there are several threads already on similar subjects, and I've just been skimming through some of them - but I thought it was worth asking a specific question or two separately in case Those Wot Know Stuff About Batteries can help with some direct answers.... so here goes.....

I'm converting just one or two locos to battery power and the Tam Valley DRS control - I've got the control boards and stuff now (thanks Muns! :) ) but haven't yet chosen or purchased any loco power batteries. I want to keep away from LiPo or Li-Ion, for the simple reason that I want something which can be safely charged IN the loco - I want to be able to install the battery pack(s) semi-permanently with a charging socket wired in, so I don't have to disassemble the loco every time I need to recharge the batteries. I do realise of course that this means I'll only be able to run for a certain length of time per day with an overnight recharge, but I can live with that.

My thoughts at the moment are to go with NiMhs, probably 2 x 8-cell packs in series to give me 19.2 volts output - which should be plenty to drive the Massoth XLS sound decoder (the DRS receiver handles up to 24 volts). I haven't decided 100% which locos are going to get converted first, but just for the amount of internal space available my LGB whizzy-cranks 2095 is a likely candidate.

So, question 1: what sort of cell capacity should I go for to get a decent few hours of running time from a twin-motor LGB loco, with sound? Would packs of AA cells be enough, or should I look at sub-C cells?

Question 2: any particular type/make of NiMh cells to look for? Should I avoid the unbranded "generic" types available online?

Question 3: using a 9.6 volt NiMh charger, is it a) possible, b) safe and c) practical to charge two 8-cell packs IN PARALLEL simultaneously? What I have in mind (though I confess to not having worked out the wiring yet!) is the wire the packs through a switch that toggles between running and charging modes, such that for running, the packs are in SERIES, and for charging they are in PARALLEL. Can this be done, or does it throw up any obvious problems that I've not thought of?
As I mentioned above, I'm not particularly worried about fast-charging - I'm happy with an overnight trickle charge to keep everything safe.

Over to you, chaps, all constructive advice welcomed! ;)

Jon.
 
Thanks Ross, I guessed you might be the first to answer! ;)

When I have the time, I'll search back through the old threads - I'd just hoped to get some specific answers here in an easily-digestible form.
What do you reckon about the series-running, parallel-charging question? Having been scribbling around with a few wiring ideas I can see it's not going to be the easiest thing to connect up, I think I might need a four-pole switch (four pole double throw centre-off?) - but assuming I can eventually figure that out, if I connect two 9.6 volt packs in parallel to a 9.6 volt charger, will the charger "see" it as one big battery of double the mAH capacity, and is there any kind of risk involved in parallel charging, like one pack being full before the other? If charging in parallel is a no-no for any reason, should I just get a 19.2 volt charger instead, if you can get such a thing?

Jon.
 
Charging in parallel is definitely a no-no.
Others will explain why.
A smart charger for 12-20 cells can be obtained from Peter Spoerer.
Mine takes about 4h to charge a 16 cell pack.
I find 7-day shop NiMH cells ok. They do a 2900mAh type.
Possibly better are their Good to Go "eneloop" type, but slightly lower rated.
If you want ready-made packs, there's Peter Spoerer or Strkalite.
 
Thanks Rob - I'd be interested if anyone can explain (in simple terms!) why parallel charging is a bad idea - is it to do with one pack trying to feed into the other? - but I'm happy to accept that you're right! All the rest of your suggestions are very useful too - will investigate further along those lines.... :)

Jon.
 
Thanks Ross, very handy! Makes sense now... Always useful to know WHY you shouldn't do something.... ;)

OK, so it looks like 2 x 8-cell packs connected in series and installed in the loco would be the way to go, trickle-charged at first to "condition" them, then medium/slow charging as required..... this SHOULD be a safe enough setup to charge the batteries in-situ via an external charging jack from a good quality charger that will do up to 20 cells, yes?
A simple DPDT switch to toggle the batteries between their charging jack and the running feed into the DRS receiver, plus of course a second DPDT to switch the loco between track pickup and battery power. Must ensure that these are wired so that it is physically impossible to ever have the battery and the track power connected to each other under any circumstances!

Anything blindingly obvious that I've forgotten? ;)

Jon.
 
You might consider not using regular NiMh cells. They self discharge at a prodigious rate.
By all means use the Sanyo Eneloop NiMh - Alkaline hybrid batteries. Limit max charge/discharge rates to no more than 1 amp and they will last just fine. Any higher and the life span, in terms of how many recharges can be achieved, will be severely curtailed.
 
Thanks Tony - what sort of battery setup would you recommend for applications drawing MORE than about an amp, then? An LGB 2-motor loco with both motors in good condition might only pull an amp with a small to moderate trainload behind it, but I suspect that something like the Piko Kamel with its non-Buhler motors may well need a good bit more oomph, especially with a reasonable train behind it?
The Tam DRS Rx is rated to 3 amp continuous, 5 amp brief peak, with an overload that trips at 5.6 amps according to the specs. What kind of battery type would you use in that sort of application?

Jon.
 
Hi Jon.
Here in OZ we can still get Sub C NiCd batteries. They are fine where there is a bit of room. Otherwise I am now starting to use Li-Ion packs which cost roughly the same here for similar capacity and voltage.
A Sanyo 5s1p 2600 mah 18.5 volt pack costs A$189 which I know is expensive. However they are Sanyo cells and will be good quality. The genuine batteries always cost more anywhere you buy them.
You may have to shop around on the WWW to find better deals.
 
Jon.
[/quote]

Jon,

As you know may I've done a Piko BR204; I used a LiIon rated at 5300 mAH although I think it really gives about 4000mAH. It handles the job fine. When I had it on the test bed I actually got a stall current (and the loco really can't ever draw more than that) averaging around 1.9A. The critical thing in sizing batteries (and adjusting you charge rate if your charge is adjustable) is not to charge or discharge above 0.5 C, where C is the rated capacity of the battery. So for a motor combination drawing 1 amp you would need a battery capacity of 2000 mAH as a minimum, and it would be better to go for more if you can.

On the self discharge issue of NiMH. as a test I fitted standard Eveready 2200 maH NiMHs to a loco, charged it to capacity and let it sit. At the end of a month I charged it again and had to put in about 480 mAH. I suspect the self discharge is not linear (although I don't know that for sure) but I would expect that it would discharge faster intially, and then again close to its discharged state, with a fairly uniform rate between those. So loss of a maximum of about 500mAH per month would seem to be a not unreasonable bet. I could live with that in a loco with 2200m maA batteries and a current draw of around 0.5A; at the end of a month sitting without use I'd still have a least two hours running and I rarely run one loco for longer than that. However, I should add that personally I normally use Eneloops!
 
Just remember that the self discharge rate can vary between brands. Also, each time it self discharges that is one life off the total number of re-charges that could be achieved when new.
 
Tony and Spoz, thanks for your input.

So if you're not going to use a NiMh fitted loco for a while, is it best to discharge it (either by running till nearly-flat, or with a discharge function on a smart charger?) and then store it like that, giving it a full charge-up just before you want to start running it again?

Jon.
 
If you must use NiMh choose the hybrid LSD types.
If you know you are not going to use a loco for some time IMHO it would be best to keep it charged.
Again, IMHO opinion I firmly believe the powers that be succumbed to industry pressure to force NiMh onto the public knowing full well they are half as good as NiCd in terms of longevity. The excuse of course was they simply had to do something about the disposal of NiCd batteries which are of course toxic. A Win - Win for industry.
I know of regularly used NiCd SubC batteries that have lasted for 17 years with commonsense application.
Just remember;
NiCd = 1,000 recharges.
NiMh = 500 recharges, at best.
You can see why the industry wanted them sold instead of NiCd.
Yes, NiCd could develop that dreaded memory effect, but only if they were rapid charged when partially discharged. In any case, that memory effect could be broken.
 
Yes, I generally agree about NiCds although they are becoming challenging to get here in this state at least; generally need a specialist battery supplier as even our local Jaycar doesn't stock them any more. Battery world will still supply but they order - although having said that I saw some in Woolies on the weekend.

I would certainly keep whatever battery is in use in a state where it it is not fully discharged although I don't think I'd have a "charge it once a month whether it needs it or not" policy either. A fully discharged battery tends to suffer corrosion effects from the chemicals therein over time and that leads eventually to rupture of the containment vessel and leakage of the contents, which is turn can lead to all sorts of nasty outcomes inside the device in which the battery is fitted. Electronics, for example, hates it.

I normally run each of my locos more often than once a month so it's not a significant issue; although the Thomas stuff only gets used when the grand kids visit in a time space which enables them to get out and play, which can be at intervals of longer than a month. I do keep a chalk board where I record the charge date (and also the r/c battery change date) for each of my locos. I've been embarrassed in the past by either an uncharged loco or a dead controller and it's easier if I can look. That's why I did the test - on the basis that if a plain vanilla NiMH was OK for a month then an Eneloop (or a LiIon) should also be fine for that period. It allows me to keep track and touch wood no embarraments since (I really should not have said that!).
 
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXAZZS&P=0

This charger charges 2 Nicd or 2 Nimh at the same time!
 
I'm only feeling my way down the battery field and am probably a tad cautious.

On the basis that fast charging is not the best way to proling battery life, I have always looked for intelligent chargers that tend to take longer to deliver the full charge.

That means, that you're not going to be able to re-charge a loco during a running session (a bit different to the RC car world) so the battery set up is looking to be able to run the loco for 2 - 4 hrs.

My orignal 0-6-0 had 12v sub Cs rated at 2300 mAh and would run for a good long time (over 4 hours once I had sorted the gearing)

My 45 tonner with twin motors has 14.4v AAs that are rated 3000 mAh LSD (low self discharge - from Brian Jones) and this will comfortable run for 4 hours with 5 or 6 bogie cars behind.

I have an Ansmann charger that is good up to 12v, that can adjust to eithre polarity, and I have a 14.4v charger that requires correct polarity on the charging socket.

Gearing for battery locos is crucial and I misunderstood the principles. A motor is more efficient, i.e. using less current, when it is spinning freely on a low gearing. A motor will draw much more current, and hence drain battery power if it is required to labour on a high gearing.

So for drivers around 30 mm diameter, we should be looking at gearing of approx 1:35, around 25 mm diameter you might get away with 1:30.

The Banta crewcab is just being installed with 12v AAs rated at 2600 mAh - we'll see how this works, should be OK on a como motor with head gear set (not sure on the ratios but Essel won't have got it wrong).

The next challenge for conversion is the 2-6-2 with the hefty Buhler 7 pole motor running on a 1:50 gearbox. It draws current at teh top end, and so I'm thinking of a 19.2 Lipo, which will need it's own charger.
 
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