diy battery tender on the cheap

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Forum Name: General Discussion
Forum Discription: General Mobile Electronics Questions and Answers
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=130590
Printed Date: May 15, 2024 at 6:54 AM

Topic: diy battery tender on the cheap

Posted By: tedmond
Subject: diy battery tender on the cheap
Date Posted: February 13, 2012 at 12:39 AM

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
posted_image

Laptop PSU 12v @ 3A
posted_image

HID male/female connector as a quick disconnect (optional)
posted_image

Quick disconnect apart
posted_image

Checking voltage output 12.13volts at 3amps when completed
posted_image

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Ted
2nd Year Tier 1 Medical School
Still installing as a hobby...pays for groceries
Compustar Expert

Replies:

Posted By: howie ll
Date Posted: February 13, 2012 at 6:40 AM

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.

-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Posted By: tedmond
Date Posted: February 13, 2012 at 1:26 PM

thanks, you did teach me a few things posted_image

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.

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Ted
2nd Year Tier 1 Medical School
Still installing as a hobby...pays for groceries
Compustar Expert

Posted By: howie ll
Date Posted: February 13, 2012 at 1:32 PM

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).

-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Posted By: kreg357
Date Posted: February 13, 2012 at 7:13 PM

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............. posted_image

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Soldering is fun!

Posted By: tedmond
Date Posted: February 13, 2012 at 9:49 PM

@ 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

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Ted
2nd Year Tier 1 Medical School
Still installing as a hobby...pays for groceries
Compustar Expert

Posted By: howie ll
Date Posted: February 13, 2012 at 11:58 PM

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

-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Posted By: tedmond
Date Posted: February 16, 2012 at 9:21 PM

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

Posted By: hemiboy29
Date Posted: February 16, 2012 at 9:40 PM

awesome thread thanks

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Chris G.

Posted By: howie ll
Date Posted: February 16, 2012 at 11:36 PM

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.

-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Posted By: 04nata
Date Posted: February 23, 2012 at 4:05 PM

Where are the diodes in the pic, and is there anything special about those?

if I go to radio shack do I just say I want 2 each of a 6 amp diode? and is there a right or wrong way to install the diodes?

evrything else makes sense.

-------------
2004 Hyundai Sonata
Kenwood KDC-X599 HU
2-Sundown X-18D4
2-SQ Q4500.1
2-SQ Q90.4
1-Massive DBX4
8-Niche 5.25 mids
8-Niche Tweeters
4-Skar 8" mid-bass
OhioGen 220a alt
OhioGen 350a alt
156.0

Posted By: howie ll
Date Posted: February 24, 2012 at 12:51 AM

You don't see them in the pictures.
Basically yes though you should have the knowledge.
Your third question, please read up everything on this site about diodes before attempting to use them, your knowledge appears remarkably non-existent.
Hello Ted and K, etc. been in intensive care all week with respiratory system failure. I
Came out with missing hair gone, no smokes all my senses back in better order, 15 lbs lighter, also aches and pains missing though I'm sure that's the anti-biotics and heavy dose steroids.

-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Posted By: 04nata
Date Posted: February 24, 2012 at 11:24 AM

Well I don't think that the put-downs were neccessary Howie, isn't the reason this forum is here, for people to learn about these things and be able to do it without being ridiculed?

-------------
2004 Hyundai Sonata
Kenwood KDC-X599 HU
2-Sundown X-18D4
2-SQ Q4500.1
2-SQ Q90.4
1-Massive DBX4
8-Niche 5.25 mids
8-Niche Tweeters
4-Skar 8" mid-bass
OhioGen 220a alt
OhioGen 350a alt
156.0

Posted By: howie ll
Date Posted: February 24, 2012 at 12:56 PM

You're right but with the number of posts you've made I wouldn't have expected such basic questions, you're certainly no rookie.

-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Posted By: 04nata
Date Posted: February 24, 2012 at 2:02 PM

oh, I guess I took it the wrong way, sorry.

when it comes to resistors and diodes and the such I am ignorant, In high school I think I was probably stoned during electronics class.

This is a great idea so I will read up on diodes and make one of these,,,,,,,,,,,,,,,,,,hopefully

Posted By: 04nata
Date Posted: February 24, 2012 at 4:10 PM

Radio shack no gots on the 6 amp diode, maybe Fry's electronics?
I read the diode section and think I understand, although my 2 laptop chargers are 18.5 volt, is that too much?
I also have one that puts out 5v-24v but I think it is auto sensing and has an 8 pin connector.

-------------
2004 Hyundai Sonata
Kenwood KDC-X599 HU
2-Sundown X-18D4
2-SQ Q4500.1
2-SQ Q90.4
1-Massive DBX4
8-Niche 5.25 mids
8-Niche Tweeters
4-Skar 8" mid-bass
OhioGen 220a alt
OhioGen 350a alt
156.0

Posted By: howie ll
Date Posted: February 24, 2012 at 4:14 PM

None of the chargers you mentioned would do the job, I'm still trying to work out why we need diodes here, also forget 6 amps, you'll most likely come across 1 amp 1N4XXX and 3 amp 1N545XX.

-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.