Charging Power Tanks.

[LukeSkywatcher]

Hi all

Just want your advice.

I bought my 7Ah power tank back in early december. I've used it quite a bit since then but nowhere near the 7hrs full charge. Today i decided to charge it as it made my scope seem a bit sluggish. So i plugged it into the mains and the red light to indicate charging came on. This was very quickly followed by the green light indicating that it was fully charged.

Now!!!!!!!!!.............

Should i leave it charging or should i unplug it? Its been charging for about 4 hrs.

Any danger in leaving it charging if it says it is fully charged (which i doubt it is fully charged).

Thanks in advance.

Paul

[Uplooker]

Is this the first time you have charged it ?????? Blimey.

What sort of power tank is it and what charger are you using?

You will be fine to leave it on charge overnight at least, I would suggest this is a good idea. You are not going to overcharge it. Depends on the type of charger (standard or trickle). If it is a trickle charger like an optimate, OptiMate UK

you can leave them for weeks.

[Carbon Brush]

I don't know how things sre arranged in the powertank as all my 12V kit is made bit and pieces.

The rule wih any gel battery is charge at 13.2V to 13.8V to achieve near enough full charge. As full charge is reached the current reduces to a low value. You can leave the charger connected indefinitely without harm.

If your charger provides more than 13.8V, then it will continue to put significant current into the battery after full charge. This causes the water (in the acid) to split into hydrogen and oxygen. In standard wet battereis, you can top up with distilled water. In a gel battery you rely on catalytic recombination. Some batteries are better than others in this respect. If you lose this (explosive) gas mixture out of the battery vent, then the gel battery is permanently degraded.

Bottom line is get a voltmeter and check the charger and battery voltage. Some chargers do output more than 13.8V so are not suitable for long term connection.

Sorry to be a pessimist. Been using gel battereis for 30+ years and put many in the skip!

[LukeSkywatcher]

Its a standard 12V Celestron 7Ah pack.

http://images.search.yahoo.com/images/view;_ylt=A0PDoS8hcWpPjgUA.7KJzbkF;_ylu=X3oDMTBlMTQ4cGxyBHNlYwNzcgRzbGsDaW1n?back=http%3A%2F%2Fimages.search.yahoo.com%2Fsearch%2Fimages%3Fp%3Dcelestron%2B7ah%26fr%3Dmoz35%26fr2%3Dpiv-web%26tab%3Dorganic%26ri%3D0&w=536&h=505&imgurl=www.optcorp.com%2Fcart%2Fproductimages%2FPowerTank12-L.JPG&rurl=http%3A%2F%2Fwww.optcorp.com%2Fproduct.aspx%3Fpid%3D2360&size=31.1+KB&name=Celestron+12V+7AH+Power+Tank+-+OPT+Telescopes&p=celestron+7ah&oid=7f9ab5f36dff650d80cb5b33528c1f84&fr2=piv-web&fr=moz35&tt=Celestron%2B12V%2B7AH%2BPower%2BTank%2B-%2BOPT%2BTelescopes&b=0∋=21&no=0&tab=organic&ts=&sigr=11crv2j68&sigb=132cnv4t6&sigi=11kj9iplr&.crumb=jeLZPDgg.xV

[mike.brightmore]

In my experience if these power packs are allowed to fully discharge then they won't hold the charge when you try to charge them up.

[terrym2002uk]

To be honest the supplied charger with these powertanks are naff. I use a ctek smart charger to charge my sw 17ah tank via its jump leads. Much better results.

[Carbon Brush]

If you look in the small print of some start/charge or powertank type products, you may see a gentle warning about not leaving the mains charger permanently connected. this is because the charger outputs more than 13.8V and will wreck the battery, as described in my last post. Some box makers don't even give this warning.

Discharging gel batteries. Another issue.

Most battery manufacturers recommend running their batteries down about 1.8V/cell. This means a 12V battery dropping to 1.8x6 = 10.8V. Much scope kit will be showing motor performance issues by this time.

You can discharge further to get the last bit of energy, but there is risk.

If you completely flatten a battery then recharge fairly soon. Next day for example, there is generally no problem.

If you leave the battery well discharged for longer, then it may become 'high internal resistance' and have low capacity. assuming you have meters to measure, then you will see it taking a low charge current. The voltage after charging appears OK. However, when you connect a load the battery becomes discharged after a short time, and the voltage drops if you take higher current. For example it may run a drive a track speed. But show problems when you connect dew heaters.

If you think of experience with car batteries - same chemistry but not gelled you may have seen this effect. If you leave your headlights on, then within hours a recharge or jump leads and get you going, then no harm is done. Leave your 'Sunday' car in the garage with the interior light on for a couple of weeks and the battery often won't recover.

There are methods that can be used to recover battereis after deep discharge. But they are not guaranteed.

Lead acid batteries do also have a limited life, even when looked after properly. So think of them as a service item, rather than being good for many years.

Understand your batteries and buy a voltmeter. do not assume that the kit manufacturer is doing the best for the battery. He has to make a product for a price. cutting corners on the charger is a very significant saving.

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