[MI2600]

There was a recent electrical thread that had a post containing info on making a homemade battery tender. I've searched all over w/o success.

Anyone know where it's at?

[willys36@aol.com]

I am the first to head to DIY but trickle chargers (I assume this is what you mean by a 'battery tender') are so cheap why fool with DIY?

[willys36@aol.com]

Double post!

[MI2600]

This idea used one of those small chargers for tape recorders or whatever and I happened to have one (or three). Then, all that was needed was some alligator clips.

[daimon1054]

willys the battery tender uses a small chip to only send charge to the bat when needed. The trickle charger always sends current and even though it is a small amount over time can damage the battery. I don't think you are going to make the battery tender in the garage a trickle charger sure, if you have 12 volt radio power supply then all you need to do is either clip it to the bat or make a cig lighter plug and stick it in there.

[302 Z28]

There is a battery mangement system with the brand name "Battery Tender". I have several, including two Battery Tender Jr. models. A 12v wet cell battery needs a constant charge in order to be up to it's potential. The Battery Tender line charge a 12v wet cell to a predetermined voltage, sense the voltage fall off at full charge and automatically switch to a "float" charge. The float charge is not a trickle charge, it is a constanty variable reduced charge rate designed to maintain a specific voltage in the battery. A constant charger, be it trickle or float WILL NOT damage a battery if the chrager is engineered correctly. I have had a Battery Tender Jr. on my generator for over 5 years. It sits up sometimes for 8 months before I remember to run it. It has never failed to turn over and start.

http://www.batterytender.com/default.php?cPath=11_3&osCsid=be75017ae20b5316a8a6 4f297ecd2b2e

Vince

[willys36@aol.com]

Originally Posted by daimon1054

willys the battery tender uses a small chip to only send charge to the bat when needed. The trickle charger always sends current and even though it is a small amount over time can damage the battery. I don't think you are going to make the battery tender in the garage a trickle charger sure, if you have 12 volt radio power supply then all you need to do is either clip it to the bat or make a cig lighter plug and stick it in there.

Hmmm . . . . Here are the specs or the charger/tender I referenced above on the ebayY auction,

Suitable for 12 Volt wet-lead-acid,
Sealed-lead, gel, and absorbed mat
Batteries.

One LED turns Yellow, and Green to
Indicate charging status.

Automatic cut-off and then true float to maintain a full charge indefinitely
Without harming the battery.

Electromagnetic interference (EMI) is
Controlled; TV, Radio, and other
Appliances are not affected

Also my experience is that most good quality commercial battery chargers taper and shut off as battery comes up to speed. For example I have a medium grade trickle/10amp/50amp charger at home that modulates the current based on battery voltage and turns completely off when fully charged so does no harm.

If you are doing any hot rodding/car building at all I recommend you get a charger similar to mine w/ +10amp capability. Great for charging batteries for sure but is an invaluable 12V power supply to test electrical systems when a battery is not conveniently avaiable. For example, I am using mine currently to trouble-shoot my EZ wiring harness in my pickup project. I am still several months away from needing a battery and my charger is a great substitute for problem solving.

Incidentally, here is the thread you were looking for in your original post.

[GypsyR]

Harbor Freight had 1 amp "battery tenders" on sale about 6 months ago. I bought two for $8 each. Both have been in continous service since, one on a motorcycle and one on various car batteries in the garage. I find it pretty hard to justify screwing around with light bulbs and Radio Shack parts to save $8 plus a couple of dollars shipping.