Can I use my power supply to charge a car battery?

Discussion in 'Mobile Radio Systems' started by KC8BWS, Feb 3, 2011.

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  1. KB0YYO

    KB0YYO Premium Subscriber QRZ Page

    If both batteries are dead flat you should consider replacing them asap. When a battery goes flat dead it's life expectancy is short. It will leave you stranded again and I bet not in a good place.
    I carry a jump start battery system in the truck and about once a month I check and recharge the battery. It will start a 500 hp diesel.
  2. W2ILP

    W2ILP Ham Member QRZ Page

    The best battery charging power supply should have the capability of adjusting its voltage and a have a current meter. You can then adjust the voltage for a trickle charge that will not exceed the power supply current capability. As the battery gets charged the current will slowly decrease and you can readjust the voltage. This may take some time but it is safer than a high current quick charge. Quick charging at high current may cause a bad battery to overheat or have its plates buckle. Batteries that overheat can even explode...thus I prefer to trickle charge, starting with as little as 2 or 3 amperes. A chargeable battery will take a trickle charge regardless of the temperature. If it won't charge when the ambient temperature is below freezing it won't ever charge and you will need to buy a new battery.

    w2ilp (Increase Load Potential)...slowly.
  3. KC9TLP

    KC9TLP Ham Member QRZ Page

    Using a power supply to charge batteries is a gamble if it has crowbar protection built in. Its great to protect the power supply and associated gear, but throws a dead short on the output and your now semi charged battery, typical winner: the battery . If you have a adjustable power supply, raising the voltage to 14.7 volts and putting a blocking diode prevents this, but it needs to be rather high amperage to not melt down. The average v-6 car draws 220 amps when cranking for a gm 3800 v6.
  4. K8ERV

    K8ERV Ham Member QRZ Page

    In addition to the above info, it is a good idea to put a large diode in series with the supply to prevent the possiblilty of the battery feeding current back into the supply. Some supplies don't like that one bit.

    TOM K8ERV Montrose Colo
  5. G0GQK

    G0GQK Ham Member QRZ Page

    Best thing to do is knock on a few doors and ask if they have a battery charger that you could borrow for the day and offer a couple of dollars for the loan or buy their dog a bag of biscuits.

  6. W0IS

    W0IS Ham Member QRZ Page

    It looks like it's been a while, so hopefully the original poster got his battery charged up by now.

    As others have noted, since the first battery charger got fried, I guess I wouldn't want to risk frying the second expensive battery charger (although I've seen it done, with no damage done).

    If you're like most hams, though, you probably have a bunch of "wall-wart" power supplies floating around the house. Chances are, one of them puts out about 12 volts. If you're willing to wait a day or two for the battery to charge up sufficiently to start the car, one of those is probably up to the task. And if you fry the thing, you're not out much money.
  7. KC9TLP

    KC9TLP Ham Member QRZ Page

    Best approach i found to a dead battery is 2 gauge jumper cables and a running vehicle. Normally takes more time to get them out of the trunk then it does to actually get the car started.
  8. KD0CAC

    KD0CAC Ham Member QRZ Page

    Being in the auto repair bis for a few decades , I have a few questions about the original poster situation , can also use for general info .
    I use to have a formula for how much battery power , AMPs , it took to start a car and it was for gas engines not diesel , gas engine have an average of 150 lbs of compression , diesels have about a min. of 400 PSI .
    For an average car today , it takes about 130 amps to start a gas car , in warm 70*F conditions .
    Since cold temps were brought up , a battery loses 80% of its capacity at 0*F , most of the time with newer cars and all the things that suck power , in this case like the fuel pump & injectors , they will take all of the avalable capacity with nothing left over for the ignition , so no spark to light fuel .
    Now you have fowled plugs on top of all the other issues .
    When I was doing mobile service here in MN and we had -20 , -30 below F , I would make a map of all the calls and make a circle , take the battery out of the car , put it in the costumers house near heater , but the time I got done with the last one on the list , I would be back at the head of the line , put the warm battery back in , hold the throttle all the way to the floor [ for fuel injected engines , most any car made these days , that shuts the fuel supply off ] clearing the fowled plugs , as soon as I here the 1st firing , I let up on the throttle and the car starts .
    No need to charge battery , because with 80% capacity gone do to cold the costumer quits because the battery has nothing left , when it is warmed up , you just put 80% back in and batteries will bounce back a lot , because its a chemical storage device and it wants to equalize .
    Then as far as battery charges go , 1st never jump start a engine with any charger , I have repaired many chargers , they are not made to jump start a engine even so they say so on the outside .
    What happens on the inside is the high current pulled when jump starting causes a spot weld / burn through on the rectifier , after a number of jumps the rectifier is just gone / burnt away , I would get these for free from my Snap On dealer , put in a new rectifier and have a good charger for about $20 .
    If the battery is completely dead then it can take 100 - 150 amps for up to 15-20 minutes to get it to take charge , so the trickle charges are almost useless .
    As for the power supplies , there not made to put out the current a Flooded Lead Acid Battery needs to be recharged [ FLA batteries should be charged at the same rate that they were discharged ] , Power supplies are not built to put out max rating for long periods , such as charging batteries .
    Car batteries are designed to use at most 20% of there capacity and immediately be recharged .
    Were as Deep Cycles can be discharged up to 80% then recharged .
    All batteries have a cycle life , how many charge cycles before total failure , as an example if you kill your car battery about 20-50 times its dead .
    Hope this helps many .
  9. KM3F

    KM3F Ham Member QRZ Page

    Using any DC supply to rechargw an auto battery

    Answering the original question about using a Ham supply to charge an auto battery.
    The ham supply is a constant voltage design with the only current limiting it 'may' have is an over current protection circuit.
    Answer is no by direct connection because you have no control over charge current.
    The full charge current is due to the dfference between the supply voltage and the battery voltage the same as it is in an auto charge circuit. Or said another way, the ratio in resistance/impedence between the two.
    You can use the supply if you provide a current limiting resistor in series to limit the current to a safe value the Ham supply can offer without overheating over the time it takes the battery to recover as it's voltage rises, meaning the difference between the supply and the battery becomes more equal.
    Current limiting accross a series resistor occurs because there is a drop in voltage accross the limiting resistor from the current attempting to flow through it. The resistor wattage size must be high enough to handle the power dissapation.
    (Edrop times the I through the resistor = power dissapation).
    There you have the basic why and how to, if you can come up with the limiting resistor and monitor the battery voltage with a volt meter to tell when it comes up to normal level of about 14 volts or the supply output voltage and stop the charge process..
    From the above you can see it will take longer to recharge a battery this way as opposed to an auto charge system that often has as much as 100 amps to start the charge before taper begins. A Charger also has the limiting needed as well as current capacity depending on it's design capacity.
    If a battery has been frozen such that the plates have been damaged, all bets are off as to the success of recharging. Remember that even one bad cell will never let the total voltage rise to normal full charge level making the battery look like is never stops charging.
    Good luck.
  10. N3EF

    N3EF Ham Member QRZ Page

    I would love to know how to make a wheatstone bridge out of four diodes
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