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Car Battery Charger Repaired

By on July 2, 2015
car battery charger repair








Yesterday my friend brought his friend’s Car Battery Charger. A model PRO USER- EBC4. For 12V LEAD BATTERY 4A Charging.

car battery charger repair

After opening I saw immediately why this Charger did not work. A 5W 0.05 Ohm resistor was defect. The simple circuit had a signaling circuit for the front leds with a single 8 pins LM358, 4 Power Diodes that deliver the Charging current for the Battery. With the now bad series resistor to protect the Transformer from Over Charging with too large currents. Probably because the owner replaced his Car type Fuse on the Front of this Charger with the wrong value, this resistor was now an open circuit.

I phoned my Electronics Shop in my Hometown’s Centre if they had this bigger resistor in their shop. To be sure I didn’t went there all the way for nothing , I always phone up first because most of the time I had to pre-order a component to get it weeks later. And because it was a device from someone else, I didn’t want to wait three weeks or more on a simple component.

car battery charger repair 1

But this time I made this resistor myself by using four 0.22 Ohm 3 Watt resistors connected parallel. This makes a replacement resistor of 1/ (1/0.22+1/0.22+1/0.22+1/0.22) = 1/18,18 <=> R = 0.055 Ohm. Or ((0.22 Ohm x 0.22 Ohm)/ 0.22 Ohm + 0.22 Ohm) = 0.11 Ohm <=> ((0.11 Ohm x 0.11 Ohm) / 0.11 Ohm + 0.11 Ohm) = 0.055 Ohm. Is almost the value of 0.05 Ohm we want. (The 0.005 Ohm difference don’t really matter. The Charger will work Fine! 0.005 is just 1/1000 times 5. That’s totally Neglectable.)

We wanted a 5 Watt 0.05 Ohm Resistor. We get from 4 parallel switched 0.22 Ohm 3 Watt Resistors a Bigger 0.055 Ohm 12 Watt Replacement Resistor. Or Calculated: Power = Voltage x Current = (Voltage^2)/Resistance= (Current^2)x Resistance. One 0.22 Ohm 3 Watt Resistor gives a Umax of 0.81240 Volt at 3.6927 Amps, because 3 Watt equals 0.22 Ohm x I^2 <=> 3 Watt / 0.22 = 13.63 Amps^2 <=> I = square root of 13.63 Amp^2 = 3.6927 A.

We know that if we switch 4 identical Resistors in Parallel that the Voltage over all of them is the same. In other words P with four resistors Calculates again 0.81240 Volts but now at 4 times the current = 3.6927 x 4 = 14.77 A. And we know that P = UxI = I^2 x 0.055 Ohm =

U^2/ 0.055 Ohm <=> gives again a Calculated replacement Resistor of 0.055 Ohm 12 Watt ! In other words: Four times the Power Dissipation of 1 Resistor of 0.22 Ohm.

car battery charger repair 2

Above photo shows the replacement Resistor 0.055 Ohm 12 Watt. That replaces the old defect 0.05 Ohm 5 Watt Resistor.

car battery charger repair 3

Above photo displays the bad resistor. An original 5W 0Ohm05J (=0.05 Ohm) resistor. Without this the Battery Charger gives no Output. Probably because of short circuiting the Battery Charging Wires.

Next photos show the Charger pcb with the Bad 0.05 Ohm 5 Watt Resistor before replacing it by the previous mentioned substitute 0.22//0.22//0.22//0.22 Ohm is 0.055 Ohm 12 Watt Resistor.

car battery charger repairing

car battery charger repair 6

After the bad 0.05 Ohm Resistor was replaced by our self-made replacement as previous photo shows, the Charger worked as was expected. If this self constructed resistor with its 0.055 value now is a bit higher. 5 times 1/1000 of an Ohm to be exact more than the originally replaced resistor it could mean this less Current.

Also 5/1000 also means 1/200 of an Ohm less current. And furthermore that calculates to be only about 20 mA (which is about the current through one single Led). Because this Charger’s Maximum Charging Current of 4000 mA means 1/200th of it is 20 mA = 5 x (4000/1000)mA less Current.

By just calculating we can be sure to rule out any unwanted effects that we would not have anticipated. (Worst Case scenarios). Hope this was nevertheless an entertaining and not to complicated article.

Until next time.








Albert van Bemmelen, The Netherlands.


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  1. Mark

    July 3, 2015 at 8:15 am

    Hey Albert,

    Thanks for thinking out of the box. It is good to use all the calculations to make sure that we have covered all the bases. there is nothing worse than doing a modification that works, only to find that it won't cope with wattage requirements.
    Thanks for the article.

  2. George

    July 4, 2015 at 9:27 pm

    You better put 2 resistor of 0.1 ohm 3w in parallel and you get exact 0.05 ohm and 6 watt.Good luck

    • Albert

      July 6, 2015 at 12:25 am

      You're completely right George! But I only had these 0.22 Ohm 3 Watt resistors recently bought from China in my Electronics Shack. And because I did my repair for free (I do not ask my friends for any money if it does not cost me anything extra). And probably my Hometown's Electronics Shop does not have these 0.1 ohm 3 Watt Resistors right away either. And anyways they are not exactly cheap so I came up with this repair solution.
      Thanks for your reply!

  3. Albert Hoekman

    July 4, 2015 at 9:40 pm

    Hi Albert, thanks for the article. This is some other stuff than fixing electronics.
    Ga zo door met publiceren.

    • Albert

      July 6, 2015 at 12:39 am

      Hi Albert, fellow name sharer,

      I actually didn't think much of this quite simple article, because I send in another article about an "Automated Optical Fan Controller" which I made for my brother's Toilet about 4 years ago. It is indeed not always only repairing or fixing as you say. And my photo was only on that article. But ended up on this one. Also another article about a Kodak Photoprinter repair wasn't published yet. Maybe to difficult for the readers?

  4. Ehsan Murad

    July 5, 2015 at 11:55 am

    Thanks for the article.Nice to know how to replace unavailable parts.

    • Albert

      July 6, 2015 at 4:41 am

      Hi Ehsan,Yes that was the purpose of this simple repair. Explaining how to replace a bad resistor with higher Power and Current from parts at Hand. If we run for every defect component to our local Electronics Shop we can't make any money ever. These formulas used, already about 37 years in my head, are simple because with Direct Current (DC) there is no Cosinus Phi phase shifting between Voltage and Current. They are in Phase. Else the formula would be P = U x I x cosinus Phi. (and it would become AC).

  5. Robert Calk

    July 5, 2015 at 1:17 pm

    Thanks Albert. I guess you have a bunch of .22 Ohm and other value resistors? I bought a bunch of different sizes below 1 Ohm and above so I could make assorted values like that when I'm in a hurry or can't find the proper replacement. Good job.

  6. Albert

    July 6, 2015 at 12:53 am

    Yes you are correct as always Robert. I had about 30 of these 0.22 Ohm 3 Watt Resistors. And because I didn't want to wait on this resistor and my repair was going to be Free of Charge (What are Friends for !).It is always nice if you are able to help someone. I also warned my Friend that his friend immediately should replace his wrong Fuse in the Front of this Charger to prevent his internal one-time Thermic Transformer Fuse from blowing up the next time. After all: My 12 Watt resistor easily would withstand any over current now !
    PS: I am very happy with my Tektronix 2465A I bought! Only the replacement LTC-7PN Battery that was send to me, although I ordered the LTC-7P one, has no protector diode with resistor internally (1N5817 + 1.6k ). So I hope it will not become a problem in future. The 7PN type is on Ebay the replacement Battery for the 7P version. (I warned Seller Bargain Bros. in Il.USA for this problem).

    • Robert Calk

      July 7, 2015 at 2:11 am

      Hi Albert,
      I'm glad you are happy with your Tek 2465A scope. I have the 2465A DV, that has the built-in DMM. My scope also uses the LTC-7PN battery. So far I have not had any problems with it. I don't think they make the 7P anymore, but I don't remember exactly. You can refer to my article when you decide to put your new battery into your scope for assistance.
      I bought my battery from,
      I can't wait to see one of your articles that has a picture of your new scope in it! Have fun.

      • Robert Calk

        July 7, 2015 at 3:44 am

        Oops, I was wrong - mine was the 7P. The 7PN won't fit right.
        I found your comments on my articles.
        I wonder if Mouser will ship to your country? The Keeper II batteries should be safe for air transport.

      • Albert

        July 9, 2015 at 12:53 am

        Hi Robert, I see you corrected your reply that you did say you put in a LTC-7PN Battery in your Tektronix 2465A DV. So far as I could see on the Photos in your article it was indeed a Black one from Mouser and those are the REAL originally LTC-7P 9 Gram types. And 7PN also fits easily in the place of the 7P on your Tek Board.

        My replacement was the yellow metal canned 6 Gram LTC-7PN type without the internal Protection Diode 1N5815 + 1.6K Resistor.
        If you look at their Datasheets and compare them you see what I mean. The Pins outline are identical but internally they aint!

        And yes the Bargain Bros. Il. USA on Ebay now will send me the correct type 7P Battery. So these Batteries sure do still exist! But are often wrongly replaced by the 7PN type. I am very glad they Ship now one to me, because other American Firms simply refuse sending one single 9 Gram Battery or ask absurd high Shipping Prices ($95 US Dollar for special UPS Shipping only, plus Battery $15 US Dollar).
        By-the-way: I read that your Scope only had run for about 1165 Hours in 30 years or so. Mine about 48thousend+873 Hours !! and was put On and switced Off about 1596 Times. The only bad thing on my scope is the green Channel 4 led that is weaker. But I'm glad that everything works as precisely and as easily as it should. (FM 90.9 MHz is 90.9 MHz between its cursors ! No deviation at all)

        • Albert

          July 9, 2015 at 1:21 am

          Oops I did it again. (I soon need to replace my laptops old overused keyboard. Or watch those big old hands.)
          I thought I wrote 1N5817 in above text but it shows wrongly 1N5815.

        • Robert Calk

          July 11, 2015 at 1:24 am

          Hi Albert.
          Yeah I made a mistake and hoped that I corrected it fast enough. Those batteries are built very well. I'm glad that you are getting the correct battery. I hope you have no problems replacing it. Just be real careful taking the connectors loose from the PCB. I used a small screwdriver to gently pry up on the bottom of the connectors while pulling them with my other hand.
          I think some old man had my scope boxed in the closet for a long time and his wife must have sold it after he passed away. It looks to be in mint condition and didn't even have a speck of dust inside it! It had not been used much.
          I am happy that your scope is working well.

          • Robert Calk

            July 11, 2015 at 1:27 am

            Yeah it would be nice if we had an edit function so we could correct our comments.

            • Albert

              July 11, 2015 at 5:13 pm

              Yes Robert, I have asked Jestine if it would be possible to add that option in near future. But until then he needs to clear our errors for us.

  7. Humberto

    July 6, 2015 at 8:35 pm

    Good repair Albert. I have had to use this method of connecting resistors in parallel or in series connection to obtain a value in ohms.

    • Albert

      July 9, 2015 at 12:59 am

      I was first thinking to make some self made resistor from resistance wire used in heaters, but I couln't find any. Because the value in Ohms is so low it would be easy to make some kind of replacement 'coil'. But then it probably was not easy to solder that type of wire.

  8. Juwel

    May 27, 2016 at 7:35 am

    Would anybody post the transistor lists of Ring RCB320 Battery charger ?
    One transistor missed from circuit board for corrosion.
    Thanks ahead.

  9. Tony

    February 26, 2017 at 4:26 am

    Hi I have just fuond this problem on the same unit. I find the( The 0.05 resister open circuit )Many thanks for the various solution for the repair.


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