Charging multiple glider batteries

Our club (US) keeps 8 batteries charged in two banks of 4 batteries. We
use two Battery Tender Junior chargers, one for each bank. The charging
rate is not very fast, but they have at least 20 hours between use and
often a week. Mostly this has worked pretty well, but we are more often
finding batteries that are not fully charged, even though the battery
tender is green indicating full charge. Once fully charged, the charger
just floats them. The batteries are the popular glider batteries, 12
volt 7 amp hour sealed lead acid.

How do other clubs, commercial ops keep multiple batteries charged up?

I realize charging problems can occur when one battery is damaged, won't
take a full charge or is simply dead. Or if the charging rate varies
markedly from batt to batt. It may be possible to overcharge the other
ones. Ideally each battery would be charged individually, but that is
expensive and takes more space. What solutions are out there?

On Mon, 06 Jan 2014 14:53:37 -0500, Don wrote:

Our club (US) keeps 8 batteries charged in two banks of 4 batteries. We
use two Battery Tender Junior chargers, one for each bank. The charging
rate is not very fast, but they have at least 20 hours between use and
often a week. Mostly this has worked pretty well, but we are more often
finding batteries that are not fully charged, even though the battery
tender is green indicating full charge.

Are you sure that charging a number of batteries in parallel isn't
confusing the charger and causing it to switch to the next phase earlier
than it should?

How do other clubs, commercial ops keep multiple batteries charged up?

I carry two batteries, one running T&B and radio, the other driving both
varios and a satnav running LK8000 and I use a pair of mains powered
Sunpower UK two-phase SLA chargers to charge them. Unsurprisingly, they
have differing charge states after flying and, as a result, there is
usually a large time difference between the two chargers signalling that
they are in float mode.

My club has, I think, nine batteries for the club fleet, which are
charged by a set of mains powered two-phase SLA chargers, one per
battery. When they are not in gliders, the batteries are permanently
connected to their individual chargers, which look to be in the same
performance and price range as the ones your club uses.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

On 1/6/2014 2:53 PM, Don wrote:
Ideally each battery would be charged individually, but that is
expensive and takes more space.
The excellent Battery Tender Jr. is available for around $23.00. You
can put four of them on a cheap power strip to charge a bank of
batteries and you will have spent less than $100.00 to properly charge
each bank of your batteries. That's too bulky and expensive? Really?

Also, SLA batteries don't improve with age. If ever left discharged,
they go bad very quickly. A bad battery looks exactly the same as a
good one. Some of yours may need replacing.

Hint: Because the capacity of a battery decreases over time, one symptom
of a bad battery you might notice is that it takes a charge much quicker
than a good one.

Vaughn

Vaughn wrote, On 1/7/2014 6:11 AM:

Hint: Because the capacity of a battery decreases over time, one symptom
of a bad battery you might notice is that it takes a charge much quicker
than a good one.

A weak battery, unless it was run completely flat, will take just as
long to charge as good battery that was discharged the same amount. You
have to replace the amp hours you took out, regardless of the capacity
of the battery.

What tells you your battery has lost capacity is it won't power your
instruments as long as it used to, or the voltage is significantly lower
after a flight than when it was new. You can also do a discharge test to
determine the capacity, using a resistance and a voltmeter (cheap), or a
device designed to do it automatically ($50-$150 range for that).

Regardless, considering the low cost of a decent 800 ma charger, I'd go
the "one charger per battery" route.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

On 1/7/2014 10:04 AM, Eric Greenwell wrote:
A weak battery, unless it was run completely flat, will take just as
long to charge as good battery that was discharged the same amount. You
have to replace the amp hours you took out, regardless of the capacity
of the battery.

OK, I should have said "A flat bad battery will charge quicker than a
flat good battery" precisely because you need to put fewer amp hours
into the bad battery before it is fully charged.

What fills quicker from the same tap, a large cup or a shot glass?

I have heard many folks say something like "that battery must be good
because it takes a good charge in no time at all."

Vaughn

The excellent Battery Tender Jr. is available for around $23.00. You

can put four of them on a cheap power strip to charge a bank of

batteries and you will have spent less than $100.00 to properly charge

each bank of your batteries.

For even less you can get a similar small battery charger at Harbor Freight.
They are $10 but are often on sale with a coupon for less.

http://www.harborfreight.com/automat...ger-42292.html

On Tuesday, January 7, 2014 9:38:19 AM UTC-8, Soartech wrote:

The excellent Battery Tender Jr. is available for around $23.00. You
can put four of them on a cheap power strip to charge a bank of
batteries and you will have spent less than $100.00 to properly charge
each bank of your batteries.
For even less you can get a similar small battery charger at Harbor Freight.

They are $10 but are often on sale with a coupon for less.
http://www.harborfreight.com/automat...ger-42292.html

A good battery tester helps. I recently got one and discovered that the charger I bought when I got my glider 10 years ago only puts 6 Ah into my 10.5 Ah SLA batteries. A different charger gets them up to about 7-8 Ah for my load profile. I've been running tests on some 9 Ah LiFePo4 batteries as well - pretty impressive performance so far - better than the 10.5 Ah SLA. I'll share results after I've had a chance to test them in my fridge.

9B

1st question is how old are the batteries? Under ideal conditions they are probably going to lose about 10% of their capacity within 3 years and 20% by 4 years. (Powersonic DataSheet) I typically replace my batteries every two years but have gone 3 to 4 years depending on how they are performing. Glider usage, could hardly be consider ideal usage for them so less life expectancy isn't uncommon.

Contrary to what seems to be popular opinion, I really don't see a problem with the parallel charging (especially with a low current charger) as long as your trickle charging is holding or bringing the voltage to between 13.5 and 13.8 volts. Use a meter and test this.

I will agree that a bad or weak battery may prevent the other batteries from charging properly, but then again this is really a battery problem not a charger problem.


Brian

On Tuesday, January 7, 2014 9:38:19 AM UTC-8, Soartech wrote:


For even less you can get a similar small battery charger at Harbor Freight.

They are $10 but are often on sale with a coupon for less.



http://www.harborfreight.com/automat...ger-42292.html

I'm almost always in favor of "for even less!". But in this case I gotta give HF's offering a double thumbs down - I threw them in the trash. Of the two examples I purchased, both appear ed to be non-temperature compensated constant voltage chargers that would not fully charge a 7 AH battery in good condition. Max float charge voltage was under 13 volts IIRC. Spend the extra and get chargers at least as good or better than "Battery Tenders".

http://batterytender.com/resources/float-charging.htm/

bumper

How do other clubs, commercial ops keep multiple batteries charged up?


I made this circuit some 15 years ago:
http://www.johny.dk/Soaring/Akku%20Lader.html
and put 8 of these into a 19 inch cabinet, one circuit per battery. It gives good feedback as to the state of the batteries: Too fast blinking frequency-its time to contact your battery dealer.

Johny