diy battery tender on the cheap

Just a short DIY to make your own battery charger. On my day off, I was playing with my audio system and managed to run it down pretty good. To the point the car wouldn't turn over. I could have bought a 80 dollar CTEK charger, but I just needed something to hold slowly charge/maintain the batt, as I play around with the cars audio settings. This is great as well for those doing alarm/rs as a side job. This is a basic 12v charger max output of 3 amps. Similar to any battery tender. Note this is not meant to be used for winter storage, or boosting. The intentions as temporary charger. Parts (some can be found in your house): 1- Laptop charger DC 12-14v capable of 2-5amps (14v is best) 1- Fuse holder and appropriate fuse matching output of laptop charger 2- 6 amp Diodes on both NEG and POS lines to prevent back feed 2- alligator clips for battery terminal 1- HID waterproof male/female connector (optional) Solder, Solder Iron, Tape, 15 Minutes, Multi Meter Instructions: 1) use your dmm to determine negative and positive 2) solder diodes in line before fuse on the neg and positive. band towards charger for negative, band away from charger for positive 3) solder on your fuse holder on the positive line 4) solder on quick disconnects if you want this option 5) solder alligator clips on, which will connect to the battery 6) tape up all connections 7) connect to multimeter and check if you wired it up correctly. 8) charge your battery, and see how you saved money, with a charger you probably had laying around. Wiring it all up and soldered all connections Laptop PSU 12v @ 3A HID male/female connector as a quick disconnect (optional) Quick disconnect apart Checking voltage output 12.13volts at 3amps when completed Ted

2nd Year Tier 1 Medical School

Still installing as a hobby...pays for groceries

Compustar Expert

Oh boy are you learning fast, also how to charge up that drill battery when you've left your charger at home. I use a power pack supply for trickle charging and 35amp stabilised power supply set at 13.8VDC to get that flatty back to life, constant 10amps draw, boy does it work.

thanks, you did teach me a few things is the power pack variable voltage? I might just give in and buy a ctek charge down the road, but for now, it works for me to do what i need. Ted

2nd Year Tier 1 Medical School

Still installing as a hobby...pays for groceries

Compustar Expert

The power pack supply just gives me 13.2VDC at 2 amps, the power supply has spring connectors with 6 amps, a cig socket with 10amps and 35amps all at 0-20VDC, made in the USA of course. How do think I know you can trigger a Bosch relay with 7.5 volts? (Another thread).

Nice one, Ted.  Think we all have a few old laptop chargers laying around.  Could even use it for bench testing & programming the R/S and bypass.

There is nothing worse than getting an install all done, plugging in the fuses and..............nothing.............  

Soldering is fun!

@ Howie, seem like a big battery pack youre carrying around. Thanks Kreg, luckily I have not come across a defective compustar brain yet (keep my fingers crossed) The psu is good for low current applications. I was trying to find a 13/14 volt psu but nothing laying around that voltage. it will do for now Ted

2nd Year Tier 1 Medical School

Still installing as a hobby...pays for groceries

Compustar Expert

10 year old Mac unit, except I'll replace it shortly, it's not charging. Not so much big as heavy!

will you be able to replace the internal batt?Ted

2nd Year Tier 1 Medical School

Still installing as a hobby...pays for groceries

Compustar Expert

awesome thread thanksChris G.

Good idea, had that problem with an LED tube recently TED, it's now the "extra trunk light" illuminating my tool box area, sans batteries + 380R resistor! I'll have to open it up, check the circuitry and the battery, probably a sealed Yuasa. Ted PM me please with some rough prices, pal has a 2011 BMW looking at R/S, need pricing info on a decent Compustar R/S, Fortin INT-BMW-2 and either EVO-all or EVO-CAN. Thanks.