EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: GeoffS on September 24, 2012, 02:45:42 pm
-
As a member of a local community boating group, I've managed to end up responsible for the communications equipment. That will teach me to keep quiet about my radio background :)
Mostly it's a bunch of mistreated, hand held VHF transceivers. After repairing all the mechanical damage (antennas mostly) and cleaning the salt off, I'm left with a box of Li-ion batteries to test. I'll cycle these through the chargers but I was after suggestions as to a more thorough test method so I can discard the marginal ones.
While most of the battery packs are Li-ion. I've just noticed that there are some Ni-MH and (I think) Li-po.
-
Charge them, then leave for 2 days and see which are holding charge still ( measure voltage of each pack at start and then after 2 days of standing). This will weed out those packs that are dying, and then the rest can be discharged till cut off. That will give capacity. Charge again and repeat, this will tell if they are losing capacity with time, and any packs that are below nominal by around 20% are beyond recovery.
-
Here's were an e-load can save you a lot of work. I would charge them fresh, wait an hour or until the case temp is at room ambient temperature then discharge them at 0.5-1C. This is fresh capacity in mAh. Do the same, but wait a few days before discharge, this will give an estimate of self discharge rate. Measuring mAh is more accurate than just the terminal voltage, but terminal voltage is a quick health check.
Li ion and Li Po have calendar lives, and if more than 3 years old its near EOL, the question is, is its remaining mAh useful to your group for another X years?
NiMH can be reconditioned, by >=3 charge-discharge cycles. If the cell reaches >80% of the labels mAh rating in less than that, you can terminate cycling. If it fails 3 cycles, you can try 3 more or run IEC-61951 testing protocol that is the basis of legitimate battery maker's mAh labeling, and also slow cycles the battery 3 more times, the Maha C9000 charger/conditioner does this test, it takes about 36h to complete.
For NiMH, its ideally per cell, not as a whole a pack. You can cycle a pack, but its not as efficient [ but labor saving.] A lot depends on the cost of the pack [ my packs are $100-1000 each and servicing them by cycling individual cells and replacing only failed cells can be cost effective.]
-
Thanks for the suggestions.
I've managed to run all the batteries through the charger, and most of the batteries are marginal.
Battery voltage is given as 7.4 volts but under load, they measure between 4 - 5V and that's just receiving, most of them drop even further when transmitting.
One problem is lack of records as to when the batteries were bought so some could be well past their expected lifetime.
Another problem is irregular charging. Very often the radios are just dropped back in the office after use, sometime wet! and not put back on the charger. Charging only happens when someone needs a radio and can't find a charged one so they put it back on the charger for 10 minutes and then use it. Not a good life for a poor battery.
Chargers are all 12V and deisgned to plug into car cigarette lighter styl connectors, a dozen of these make quite a mess and I can understand people not bothering to find one, plug it in, use it. I might look at some way of setting up a bank of chargers so all they have to do is drop the radio into the cradle - hopefully drying it off first!
As it's a volunteer organisation, it's hard,if not impossible, to force people to follow a set of rules of guidelines on radio care. :(
-
It's really in their interests to look after the radios,as it may be their life at stake!
If Tassie is like WA,the sea finds lots of ways to kill you! ;D
-
Sounds like you've done the health check, and the labor for revitalizing any batteries isn't worth the returns, so maybe a better solution is to ask for funds for new batteries for the lot, and provide the organization with a recommendation for a plan to keep the batteries and devices working as long as possible in the best shape possible, with the minimal work on everyone's part.
For constant use communication devices, subject to erratic charging schedules, physical abuse, operation in weather extremes, partial charging etc., Li chemistry is a good option, despite the calendar life. NiMH can be economical but trades off in maintenance to realize that economy. As a case study consider the lowest denominator cellphone user, Li rechargeables are better bets.
Thanks for the suggestions.
I've managed to run all the batteries through the charger, and most of the batteries are marginal.
Battery voltage is given as 7.4 volts but under load, they measure between 4 - 5V and that's just receiving, most of them drop even further when transmitting.
One problem is lack of records as to when the batteries were bought so some could be well past their expected lifetime.
Another problem is irregular charging. Very often the radios are just dropped back in the office after use, sometime wet! and not put back on the charger. Charging only happens when someone needs a radio and can't find a charged one so they put it back on the charger for 10 minutes and then use it. Not a good life for a poor battery.
Chargers are all 12V and deisgned to plug into car cigarette lighter styl connectors, a dozen of these make quite a mess and I can understand people not bothering to find one, plug it in, use it. I might look at some way of setting up a bank of chargers so all they have to do is drop the radio into the cradle - hopefully drying it off first!
As it's a volunteer organisation, it's hard,if not impossible, to force people to follow a set of rules of guidelines on radio care. :(
-
Sounds like you've done the health check, and the labor for revitalizing any batteries isn't worth the returns, so maybe a better solution is to ask for funds for new batteries for the lot, and provide the organization with a recommendation for a plan to keep the batteries and devices working as long as possible in the best shape possible, with the minimal work on everyone's part.
For constant use communication devices, subject to erratic charging schedules, physical abuse, operation in weather extremes, partial charging etc., Li chemistry is a good option, despite the calendar life. NiMH can be economical but trades off in maintenance to realize that economy. As a case study consider the lowest denominator cellphone user, Li rechargeables are better bets.
Excellent advice. Safety is a major focus of the group, most of whom are experienced sailors, so making radio maintenance part of the safety regime should work. I've already implemented a log so that anyone who does take a radio out, has to make an entry as to when/where/if it was used, any problems noted ('Oh, by the way, I dropped it in the water'). Keeping track of usage will help with budgeting as we'll have a better idea when batteries need replacing.
I've still to test the batteries in some of the other radios, these are NiMh but I don;t expect them to perform any better that the Li-ion did in tests.