Discharging NiMh Charger for eZee Batteries

[flecc]

With the added interest now in using NiMh batteries on some eZee bikes, and wanting a discharging charger for myself, I've finally got round to thoroughly testing a suitable one for recommendation. This charger performs the normal charging function, but in addition can discharge the battery cells nearly down to 1 volt per cell to refresh them and get the best battery life.

All NiMh batteries benefit from refreshing in this way and to this level.

In addition, it can maintain a trickle charge at end of charge of less than one twentieth standard rate (C.05) to maintain a battery's fully charged state over time. Read the caution on site about using this trickle mode.

Bought from the USA, the sorry state of the dollar currently means a very favourable rate of exchange, and the charger cost me just £28.20 plus P & P, which could have been as little as £36.35 total with the lowest P & P.

Full details of this bargain are on my Torq website here.
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[hobo1]

Thanks very much for that info Flecc:- just purchased one, same postage as yours.

Cheers, David.

 

[Ian]

Nice work finding and testing that Flecc, I'm sure it will be of interest to a number of people, especially those considering converting from lithium types.

A word of caution on trickle charging NiMh though, many battery manufacturers including Sanyo and Panasonic strongly advise against this, while others state the trickle current must be within tightly controlled limits and for a limited time only. I once ruined 3 sets of 4 NiMh AA's by leaving them charging at 10mA for 3 weeks, I'd hate anyone to do that with an expensive bike battery

 

[flecc]

I agree that there are differing opinions on NiMh trickle charging Ian, some very much against it and some for.

This charger has a trickle rate below 200 mA at all times, usually well below so I think it's ok in that respect. Since I don't commute and had two intermittently used batteries, I did use trickle charging regularly with the Metco charger on my Giant Lafree's Panasonic batteries for four years without any ill effect, indeed that's an excellent life, so it's difficult to give an absolute judgment on it. In fact one of those Giant batteries is I believe still in use as a backup at four and a half years old by a forum member. Clearly Panasonic aren't right about their own products in this respect.

Behind me as I type is a Pifco NiMh batteried emergency light/torch which stays on trickle charge all the time to automatically switch on when there's a power cut, not uncommon here, and also do my torch duties. That was on trickle charge for 13 years before the 600 mAh batteries died, and the replacement 1800 mAh ones I soldered into place just over two years ago are still fine.

I don't have a firm view on the issue, but as shown, it can't be unconditionally bad as Sanyo and Panasonic appear to think.

P.S. I'm going to do some experiments on my eZee batteries with trickle charge, monitoring the temperatures and voltages to determine whether an overcharge situation arises, the only way that damage can occur with trickle charging.
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[Ian]

As you say Flecc opinions and experiences do vary, I have some electronic time switches with small NiMh batteries which are obviously trickle charged without harm, but I would prefer to err on the side of caution with large batteries where the replacement cost is high.

Interestingly a Google search for "trickle charge nimh" produces a number of conflicting results, the general consensus seems to be to be careful though.

I have no doubts about the usefulness of the discharge function though.

 

[flecc]

Yes that's true Ian, plenty of conflict on this.

Pending my experiments with trickle on the eZee battery, I'll put a caution on my site page so that others can be wary. The key of course is the trickle charge rate, low enough and it won't harm of course, and hopefully I'll get some more information on this.
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[coops]

Thanks for your efforts in finding & testing this discharging charger flecc, and the usual thorough write-up on your site .

Since there is now this discharge option for Ezee NiMH, is it possible to roughly quantify how much longer battery life one could expect from doing this, as opposed to riding the bike till empty every few charges or so (and at least once every 10 charges)? i.e. if one can consistently manage to do the latter, how cost-effective is it to buy a discharger?

Clearly it must be worth it, otherwise you wouldn't have looked it out & tested it, and the convenience of not having to ride till empty (possibly at distance from home as you say) to keep batteries fairly well conditioned, is clearly a benefit too .

Is this charger also only to be used with the standard 36V Ezee NiMH, rather than a 'radical' 38.4/39.6V battery?

Thanks again,

Stuart.

 

[flecc]

It's mainly a matter of convenience Stuart, since it's a pain having to ride batteries down regularly. However, doing it with the discharger is far more effective at getting the cells properly emptied but safe.

Extra life can't really be quantified since usage varies so much. An every day commuter who will top out the maximum number of charges in a couple of years at most probably won't benefit much. An intermittent user can benefit a lot, as my over four years with two Lafree batteries and a discharging charger shows. I doubt they'd have lasted that long without the refreshing effect of discharging.

I've tested the charging on the 39.6 volt radical battery and it's fine, but a word of warning. The discharger is designed for 30 cells, so discharges to just below 32 volts regardless. On 33 cells, mine would have discharged the cells to 0.96 volts per cell. In fact that would still be ok, but it's getting marginal and that would need to be considered in any case of extra cells. They can fail at between about 0.7 and 0.85 volts per cell when discharged to that level
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[coops]

Thanks flecc, that makes the full benefits clearer now . Also its useful as a second/spare charger and the more 'leisurely' charge might also help prolong battery lifetime, I take it?

Do you discharge your radical battery then, flecc? You wouldn't use this to safely discharge it because of the marginally low discharge cut-off?

Stuart.

 

[flecc]

Yes, a more leisurely charge is best for long life.

I do discharge the radical battery and will probably do it with this as it's only just below the 1 volt per cell mark. I'll do it a couple more times with measurements to make dead sure though I'm certain it will be stable.
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[coops]

That's good, thanks flecc .

Good to know I could possibly use it with the radical battery too, should I go down that route . I'll stay tuned to hear your further test results & conclusions on stability for T-battery discharge, aswell as the trickle charging.

Stuart.

 

[Ian]

Flecc, in the case of the radical battery you could discharge through 2 or 3 diodes, the voltage drop across them fooling the charger. Another parallel diode in the opposite polarity being used for charging, possibly a schottky type to minimise voltage drop.

I have a charger from a previous bike with a refresh function, but it discharges to 28V. I intend to fit diodes to raise the cut of point to a more sensible figure... when I get round to it.

 

[flecc]

Thanks Ian, that's a good idea.

I've no problem on charging since the T bike's controller won't take the full 45.5 terminal volts when cold anyway, it's acceptable maximum being 44.5 volts. I just give the voltage a tweak down with a multi resistor dropper plugged into the charger socket, a few minutes with that doing the trick. Of course I could run the bikes input through a pair of Schottkys to drop that volt, but I wouldn't want to lose it all the time and it's no problem as it is.

I'm going to complete the discharge checks with the present setup first though.

I've started the trickle charging tests with an interesting finding that's very reassuring. The trickle is the much safer pulsed type. The charger has a quiescent consumption of 50 mA, and that is supplemented with 310 mA for under one second in three. That fixes the total trickle rate at below 100 mA, less than 1/20th rate, half the basic recommendation and if maintained thats a huge safety factor. The charger's spec does say maximum 200 mA.

There's a lot more information being monitored on temperature and voltage etc so the test will have to be conducted for days. It's on the new standard eZee battery and I'll be using the radical battery in the Q bike meanwhile, my remaining Li-ion having given up in the cold at 10 months old even on the efficient Q bike. The T bike is laid up in the garage anyway in the current weather, it's very much a fair weather pleasure bike only, like a club rider's bike.
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[flecc]

Trickle charging

I don't really need to test this any further since I've already been able to establish all the conditions and can report it's of the safest type in all respects.

However, since anyone suffering a battery failure for any reason could unfairly blame the trickle mode, I won't recommend it's use, but have also made provisions for those who might wish to use it by putting the full information on the webpage in two sections, reproduced below:

In the main text body:

Caution: Manufacturers do not recommend continuous trickle charging. Therefore I won't recommend it's use over sustained periods, though the period following a charge, which could be a few hours with an overnight charge is perfectly safe. For more on this see the foot of the technical section.

In the technical section:

The trickle charge mode on this charger is of the preferred pulse type, giving one pulse of less than a second in each three second period, the pulse strength regulated by the cells resistance. In addition, the average trickle rate of charge is below the recommended safe rate of C.05. In practice the pulses vary between 190 and 310 mA net, averaging about 270 mA. With the pulse duration less than 1 second in 3, the average charge rate is always below C.045. Use this mode at your own risk of course, since cells vary and what might be ok with most batteries could catch out the odd one.
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[hobo1]

I have bought XLR plug this morning from Maplins Flecc: good info' once more.
It is quite a while since I did any soldering, but I have still got my iron and it's working:- So your tips on the plug change are most appreciated.
It is really going to be a great help disgharging the NiMh batery with the charger.

Cheers, David.

 

[Ian]

That would seem to cover all eventualities Flecc. As said before my own experience of trickle charging Nimh is not good, albeit with AA batteries. I built a simple trickle charger to maintain up to 4 sets of batteries in instant readiness for my digital cameras, charging each battery at a constant 10mA (0.005C). Unfortunately when I came to use the batteries all 3 sets that had been on prolonged charge were ruined, including an almost new set. It could be that the charge rate was too low, those that do advocate trickle charging normally advise around 0.05C, ten times what I was using. I would have thought the lower value safe but one never knows.

I've been spurred into action and fitted diodes to my discharging charger which is identical to the Ezee charger but with a refresh button. I've fitted 7 1N4004's in the discharge direction which drop 5.4V, thats a bit more than I expected so I may need to remove some. It's currently discharging a battery so I'll have to wait and see just how low it goes.

 

[flecc]

Reading up everything about it afresh Ian, I think the constant rate is the problem with some trickle chargers. That's ok on lead acid and Ni-cads, but seems to overcharge NiMh by all accounts.

It could also be that at the very low rate of C.005 it couldn't hydrolyse and might have just set up some sort of a short state instead.

That Metco charger that trickled the Panasonic packs for four years was pulse charging, one maximum 10 second pulse in each minute, but usually less, and of course this one is also pulsing, and appears to operate in the same way as the charger I have for non-rechargeable batteries. Certainly the online information sources seem to point the same way, constant rate bad, pulsed trickle at C.05 total ok.

The discharge on this Shenzhen one is ideal, as close as one could hope, ending on 1.06 volts per cell, so no need for any alterations. Is your eZee type (HP?) charger running them too low, so needing those diodes?
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[flecc]

I have bought XLR plug this morning from Maplins Flecc: good info' once more.
It is quite a while since I did any soldering, but I have still got my iron and it's working:- So your tips on the plug change are most appreciated.
It is really going to be a great help disgharging the NiMh batery with the charger.

Cheers, David.

A pleasure David, glad that you're getting one and I'm sure you'll be happy with it. I think for most people soldering is a very infrequent event and I always like to include tips, as much just to give confidence as anything.
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[Ian]

The discharge on this Shenzhen one is ideal, as close as one could hope, ending on 1.06 volts per cell, so no need for any alterations. Is your eZee type (HP?) charger running them too low, so needing those diodes?
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The HP charger terminates the discharge at 28V so requires manual intervention before that. The bike it was supplied with had a 29 cell battery which partly explains the lower voltage. Those HP chargers seem quite common, being supplied with several makes of bike. In spite of that I've been unable to find any info on them which is a pity as one of the 3 trim pots inside probably sets the discharge voltage limit.

PS: Discharge with 7 diodes just terminated at 32.6 V, so I'll remove one and it should be fine.

 

[flecc]

That is very low, even for 29 cells, and could well just be maladjustment if one of those pots operates on that facility.

Yes, those HP chargers are very commonly supplied with many Chinese bikes, Metco and Shenzhen very much smaller players. Metco are like HP in not seeming to make any information available, and they're only contactable via agents Alibaba who block anything other than trade bulk inquiries.

Powerstream handle Shenzhen, giving full specs, and the odd Metco type, giving partial specs, but nothing from HP, so I suspect they only supply manufacturers.

Interestingly,the 2 Amp Metco type that Giant supplied with the Lafree series for a short while is now 4 Amp and no longer uses thermistors for NiMh. It auto senses how many cells there are between 16 and 24, then charges them using what they describe as a delta V algorithm to accurately charge (they claim).

Then it supplies a tiny trickle current of 50 to 60 mA, they say to to create cell charge balance.

All makes me rather nervous and suspicious.

P.S. Just saw your PS, that should be perfect now. That's a good idea on the diodes, and I might make up an intermediate jumper lead incorporating two or three for discharging the 33 cell battery. Got a line socket, but run out of XLR plugs, so another raid on Maplins due!
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