Inexpensive Gell Cell battery charger.

[X-CalBR8]

What do you guys think of the "Battery Tender JR" and the "Battery Tender Plus" line of chargers for charging smaller Gell Cell batteries? The JR. model charges at .75amps and the plus model charges at 1.25 Amps. Would the plus model charge at too high of an amperage for say a 7ah gell cell?

Here are some specs:

Battery Tender Plus
This is a 3 step charger.
Absorption Voltage: 14.4 VDC = (2.4 vpc)
Float Voltage: 13.2 VDC = (2.2 vpc)
Current=1.25 Amps

Battery Tender JR
This is a 2 step charger.
Absorption Voltage: 14.4 VDC= (2.37 vps)
Float Voltage: 13.2 VDC = (2.2 vpc)
Current=0.75 Amps

The JR model sells for about $20.00 and the Plus model sells for about $35.00. This is a much more palatable price range for a college student budget, but at the same time, I don't want to get a charger that will fry my batteries even if it means having to save up my money to get a better charger.

How many people on the forum are using these chargers to charge their Gell Cells and could you please share your experiences with them, whether good or bad?

Sorry for so many questions, but I'm still new to charging and maintaining gell cells and I'm trying to keep it all on as small of a budget as possible. Thanks guys for all of the useful input so far.

 

[LEDlightman]

get a good charger

All I can say is: get a good charger because a poor charger will fry your batteries real fast. A good charger will pay for itself in money saved from dead batteries.
Gel cells can't handle as much stress from charging, so a charger has to limit the voltage to around 14.1. Battery tender(while I have never used them personally) sound good, but the voltage is slightly higher than I would like. If you do decide to get one, get the smaller one. While it would take longer, the smaller amperage would help compensate for the higher voltage, and limit the damage, as long as you don't overcharge from charging it too long.
On a side note, when charging the battery, if you hear a hissing sound from the battery, disconnect it immediately, it's gassing, and that means it's being overcharged. Gel cells can't handle that condition very well.
I got a $75 charger from Sears, with an option for gel cells. I still have to test it out a little more, but it looks promising.

 

[X-CalBR8]

Re: get a good charger

I just ran upon the home page for the Battery Tender charger, it can be found here.

There might be some more useful info to be found there. Check it out and see what you guys think about it.

 

[robk]

Re: get a good charger

I handled some advertising for Del-Tran, the parent company that makes "Battery Tenders". It's a great product, good Q.C., clean shop, I met all the guys in charge (sorry for the pun) a few years back. You may want to email them about charging Gel-Cells, as I believe their chargers were designed for standard Lead-Acid batteries, to maintain a charge while installed in a motorcycle. Their target customers are Harley owners who park the bike in the garage for extended periods. They build these units from scratch, wind their own transformers! I'm sure they can answer any technical questions about your specific needs.
Rob

 

[Potto]

Gel Cell batteries are a very good high density battery for portable application where a fairly large power store is required.

I've used 4, 6, and 10 Amp/Hour 6V batteries for about 15 years for caving, as have a number of my collegues. The important factor to remember about gel cells is that they are voltage charged, not current charged. ie when the battery is flat it will take as much current in as the available charging source will provide. As the battery approaches its limit the charging current decreases.

By using an LM317, with a power diode for reverse protection, the adjust resistor can be set to provide 6.7 Volts to the battery, maximum (or 13.8V). ie when the battery is not connected, or at full charge, the LM317 will not allow the voltage to go higher, saving the battery from cooking from over voltage, which is what really kills a gel cell. It also means the battery can be left "floating" on charge for weeks at a time without damage.
Note: a fully discharged battery should be charged as soon as possible, preferably within 24 hours. A gel cell battery left mostly discharged for a week will never be the same again, I know, from experience.

I have also built a charger for either 6 or 12 volt batteries by using 2 adjust resistors and a dual switch to switch both the adjust and the output to different terminals.

The LM317 is a relatively simple solution to build and can be powered by any unregulated power source 2V higher than the required battery voltage.