Harbor Freight Battery Maintainer Mod
I have a TT that I store at a remote location during the winter and I bring the group 31 AGM battery home with me. I have a charger to ensure that it is at 100% SOC before it gets set in the corner of...
Forum Discussion
Yes I do agree (westend, Mex', & phunk)… a similar result can be achieved with a wall-wart. But keep in mind that my total investment is about $6. There's no way I could assemble all of the components myself for anywhere near that price. A new regulated or switching wall power supply alone would cost me $10-15, and still wouldn't give me the ability to adjust the charge voltage or limit the current to my personal preference (ie. battery mfr's spec').
This super-cheap HF maintainer incorporates a 78XX linear voltage regulator and a TIP41 to regulate current. In addition it has a S9013 transistor to turn itself off if the battery voltage is too low.
As I mentioned, in stock form it does have some minor drawbacks, specifically;
1) A fixed output voltage, which may or may not meet my needs (I have read reports from other users that indicate voltages as low as 13.1 and as high as 14.1. Mine was 13.8-13.9)
2) There is no protection to prevent the device from discharging the battery if mains power was lost (or more likely if/when the wall transformer fails).
These 2 issues are easily fixed with the addition of one potentiometer and one diode… about $1 worth of parts.
The fact remains that this maintainer does not address temperature compensation at all :M Conveniently I live in the SF Bay Area where we have very modest seasonal temperature change. My workshop is climate controlled and the voltage I selected (~13.45V) will be fine for up to around 80ºF.
At any rate, a well-regulated (bonus points for temp compensated!) float charge is always preferable over leaving a battery to self-discharge while in storage.
Cheers,
-Mark
This super-cheap HF maintainer incorporates a 78XX linear voltage regulator and a TIP41 to regulate current. In addition it has a S9013 transistor to turn itself off if the battery voltage is too low.
As I mentioned, in stock form it does have some minor drawbacks, specifically;
1) A fixed output voltage, which may or may not meet my needs (I have read reports from other users that indicate voltages as low as 13.1 and as high as 14.1. Mine was 13.8-13.9)
2) There is no protection to prevent the device from discharging the battery if mains power was lost (or more likely if/when the wall transformer fails).
These 2 issues are easily fixed with the addition of one potentiometer and one diode… about $1 worth of parts.
The fact remains that this maintainer does not address temperature compensation at all :M Conveniently I live in the SF Bay Area where we have very modest seasonal temperature change. My workshop is climate controlled and the voltage I selected (~13.45V) will be fine for up to around 80ºF.
harold1946 wrote:Ha, I guess I should said "in storage for 11 months".
An AGM battery does not need a maintainer if fully charged when put in storage.
At any rate, a well-regulated (bonus points for temp compensated!) float charge is always preferable over leaving a battery to self-discharge while in storage.
Cheers,
-Mark
