using a power supply to charge a battery.

Discussion in 'General Technical Questions and Answers' started by KC9NEQ, Oct 28, 2008.

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  1. KC9NEQ

    KC9NEQ Ham Member QRZ Page

    i have a mfj-4035mv regulated power supply.
    can i use this power supply to charge a 12v deep cycle marine battery or a regular 12 car battery?
    if so, will i need any type of additional hardware or attachment to use it?
  2. WB7DMX

    WB7DMX Ham Member QRZ Page

    if you can set the output voltage to 15 to 16 volts yes you can as long as you watch the amps and the voltage, you may need to manually adjust the voltage to keep things working.
    also you may need to install a diode with the neccessary currant rateing to prevent any voltage feed back to the regulator circuit of the power supply.

    if you can't do any of the above, then your answere would be a definate NO.
  3. K7JEM

    K7JEM Ham Member QRZ Page

    Actually, it should work OK. Turn the supply on, and adjust the supply to near the battery voltage. Then connect the supply to the battery. Then crank up the voltage to 14v or so, making sure the current doesn't exceed whatever rate you want the battery to charge at. You may have to adjust the voltage again as the battery gets charged.

    Since this model has an ammeter built in, it should be really easy to do.

  4. W5HTW

    W5HTW Ham Member QRZ Page

    Yes, but I would not attempt to use it to charge a badly discharged battery. The initial current draw would likely be excessive. That supply has a fuse, but if pushed to deliver a sudden demand of 30 or 40 amps, there could be damage.

    To charge a slightly discharged battery, not a problem. Do as JEM says. To maintain a charge on a battery, (and I have used that exact supply to do this) simply set the voltage control at 13.8 VDC and it will draw only the current necessary to keep the battery operational.

    If your battery is badly discharged, a standard automotive charger is best used to return it to full charge. That has current limiting and will not cause damage to either the charger or the battery.

  5. K7JEM

    K7JEM Ham Member QRZ Page

    That is the reason to initially set the voltage to match that of the battery, THEN gradually bring up the voltage while watching the ammeter.

    I have done this many times, and it works FB. As long as the output of the PS is not exceeded, there won't be an issue.

  6. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    There's some risk doing this.

    Car batteries, in fact most all batteries, are best charged by pulsating DC, not pure (filtered/regulated) DC, as you achieve the same charge levels without dissipating as much power in the battery. In an automobile (that's running) or even a high quality automotive battery charger, what's applied to the battery is never pure DC.

    A transformer and rectifier wired in series with known resistance wiring to the battery terminals makes a better charger than a regulated power supply does, and can protect the battery by virtue of calculated current limiting (from known wiring resistance).

  7. WA9CWX

    WA9CWX Ham Member QRZ Page

    I have used marine deep cycle batteries for decades.

    I am currently ( no pun intended) using a pair of 6 volt golf cart battereis. I don't use them for much anymore, but I always keep them for a back up, and have a FEW rigs hooked up to them.

    A proper charger for maintaining them is dirt cheap. Also, a simple timer, set to accomodate the re-charging, based on how often you USE them, is easy and simple.

    IF you are doing a LOT of use/re-charging, take extra caution for the ventilation. Otherwise, at a slow rate, and just a few minuets twice per day, there is little to worry about. Simply a slightly open window will take care of any gasses for minimal charging.
  8. K7JEM

    K7JEM Ham Member QRZ Page

    There are plenty of chargers that are "pure DC". ALL telecom chargers are well filtered DC, and are totally capable of running delicate loads with no battery bank attached.

    I don't know where you are coming up with the "transformer and rectifier" being a better charger, that's simply not true at all. They will work, but they are far from ideal, and a good way to overcharge a battery, if left on for long periods.

  9. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    ::I tried that after a chili dog but it didn't really work.:p
  10. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    ::ALL telecom chargers are not well filtered DC, Joe. I worked for AT&T for years designing this stuff: The battery chargers are actually called "rectifiers," not power supplies, because for 50 years all they were were rectifiers and had no regulation. I still have several, made by Sorenson, MagneTek and others, right here.

    A regulated power supply without protection circuitry will overcharge a battery faster than a simple rectifier.
  11. K7JEM

    K7JEM Ham Member QRZ Page

    How can a regulated supply overcharge a battery? If it is set to 13.8 volts, it would be hard to do. A transformer and rectifier can easily do that, however, since they don't regulate the final voltage.

    I opened up two Lorain and one LaMarche telecom chargers that I have sitting right here, and they all have thousands of microfarads of capacitors in them. Maybe in the stone age they didn't have capacitors, but for the 30+ years I have been in the telecom industry, they have all been well filtered and well regulated.

    These units regulate the output voltage to better than .1 volt, under any load up to the maximum. And they stay online for years at a time, with no overcharging.

    If what you were saying was true, we would be better off to scrap these things and buy some transformers and rectifiers, and a calculated series resistor.

    BTW, we still call the chargers "rectifiers", and have for as long as I've been around. That doesn't imply, however, that all that the thing does is rectify AC. Most of these are filled with additional electronics, way beyond simple transformation and rectification.

  12. ZL3GSL

    ZL3GSL Ham Member QRZ Page

    The ideal battery charger has both current and voltage regulation. Some have a computer to give different voltages for different stages of the charge of a lead-acid battery.

    A "standard automotive charger" is best referred to as a "battery boiler" and stored in the recycling bin. With no voltage regulation, the voltage continues to increase past the gassing point for the battery if left unattended. A deep cycle "wet" battery will then lose the gas, which must be replaced with distilled water. A "sealed" gel type battery will lose the gas, which can't be replaced, and its capacity. One time will ruin it.

    A voltage regulated supply makes a good battery charger. If you're concerned
    about initial current on a discharged battery, put a few ohms resistance in the line.

    It's safest to set the voltage at 13.8 -- a lead acid can "float" on a charger at that voltage "forever" with no harm ensuing. You will get faster charging by using a higher voltage initially (never over 14.4) and when the terminal voltage reaches 14V, turn the charger down to 13.8V.

    The Battery University will tell you more than you have ever wanted to know.

    The disagreement about telecom battery chargers is probably a generational difference. The old "clackety clack bang" exchanges with a battery room full of open glass cased lead acid batteries and 48V distribution with 1/2" by 2" copper busbars to run electromechanical switches could use fairly crude chargers. A modern exchange, which is really an electronic, computer uses less power and needs cleaner power.
  13. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    ::You're right about this being "generational," that's true. However, modern SS switches and telecom gear really don't need cleaner power, or even regulated power -- at all. Reason is, telecom stuff is still -48Vdc nominal input, but absolutely nothing sensitive or critical actually runs on the 48V. The 48V rails connect to switchmode power supplies in the NEBS equipment racks, which then output all the actual circuit-needed voltages, which include 5.0 and 3.3v buses and going forward will likely include 1.1v buses as well. Those power supplies, which actually power all the equipment, can tolerate an input voltage of -36Vdc to well over -48Vdc (most are specified to tolerate an input range of -36 to -72V, and work fine at any voltage in that range). All the filtering and regulation comes from those supplies, not the battery chargers. The chargers need "nothing," technically.

    When I was designing this stuff, when the change was made to regulated power supplies for use as battery chargers (and yes, I understand they are still called "rectifiers" to this day -- a throwback, I guess), the change was made not because they needed to be regulated, or even filtered: It was made to save energy by increasing power factor as close to 1.0 as possible. The "dirty" old rectifiers could have p.f.s lower than 0.5, which isn't very efficient use of the mains. As electric power became more expensive, more thought was given to everything consuming it.

    Still, we never directly charged the battery banks with pure DC. The chargers delivered pure DC, alright, and that drove PWM circuits which pulse charged the batteries. The PWM frequency was very low, on the order of 400 Hz. Since the batteries could technically deplete to 1.5V per cell (36V per bank) and still power everything just fine, there is a huge tolerance for power outages that can last days, even weeks for most installations. Very remote sites that may not be serviceable for a long time after a failure (such as a natural disaster) usually have auxiliary generators collocated.

  14. W5DXP

    W5DXP Ham Member QRZ Page

    100% correct. That's what I have been doing for a quarter of a century. My Astron RS-20M will not power my SG-500 amp. But my deep-discharge marine battery being charged by the RS-20M will supply the SG-500 power with no problems. And when AC power fails, I still have battery power with no switchover required. I also have a parallel solar panel charging the battery with no problems.
  15. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    ::I'm impressed a marine battery can handle this load, unless you only work SSB (small duty cycle) and don't do a lot of transmitting. What are the details of that battery? And how long does one last?
  16. WB2UAQ

    WB2UAQ Ham Member QRZ Page

    I also have been running with a battery and charger in parallel with the HF and other rigs. Two batteries needed over about 20 years. I run the voltage a 13.5V down a bit from what I used to and it seems to require much less water.
    The homebrew charger is what Steve, WB2WIK, describes----pulsating DC. There are two SCRs. A large main SCR pulses current into the battery while the other monitors the terminal voltage using a zener diode as a reference.
    When the batt terminal voltage reaches 13.5 V the smaller SCR holds off the large one. If you were to monitor the current after the battery is fully charged, you'll only see a small slug of current going into the battery every 5 or 10 cycles of the 120 cycle pulses. The rest are being held off. When I turn on a rig, the current slugs increase in rate and width enough to maintain 13.5 V. NO computer needed :) it is fully automatic. The circuit I am using is from some 1960's GE SCR data book. I modified it over the years to add a bit of temperature compensation and I added a relay to completely isolate the battery from the charger when AC power is off. I felt better opening up the ckt all the way but the ckt can be designed to keep the leakage back into the charger to a very small level. My 2 cents. 73, Pete
  17. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    ::Yep, that works and is much battery-friendlier than using DC for charging simply because the battery dissipation is reduced, and heat is the enemy of batteries of all designs, including lead-acid cells. This is why car batteries in Phoenix typically last 2 years, even if they're very good ones that would last 4-5 years in Denver.

    Your circuit is old, Pete! Nowadays "smart chargers" that do all that electronically using microcircuit controllers only cost $49.95 and accomplish the same thing. I have a 200A "smart charger" that was about $150. Yes, it uses a PWM to pulse charge the battery.

  18. K1VSK

    K1VSK Ham Member QRZ Page

    There really is no such thing as a "marine" battery although some battery mfgs make hybrid deep cycle/start batteries and label them as such. What I assume he means is 12V deep cycle, or 6V "golf cart" batteries, the latter being the current conventionally accepted boat battery.

    Deep cycle batteries can be had in sizes up to almost 1000 amp/hrs so powering a modestly rated ham transmitter isn't a real problem. The common practice is to connect multiple 6V batteries in parallel/seried as 4 small golf carts connected as such will yield over 400 amp/hrs.

    Regarding leaving them on charge continuously, or charging them improperly these practices are the most common reasons batteries fail or prematurely get killed. Constant charging promotes sulfation in wet cells and as the old adage goes, "batteries don't die, they get murdered".

    By the way, where does one buy a 200 amp rated 3 stage "smart charger" for $150?
    Last edited: Oct 29, 2008
  19. K8ERV

    K8ERV Ham Member QRZ Page

    I have read that some mfrs do sell a "marine" battery that is supposed to have a more rugged construction to withstand the pounding that a boat can take from the waves. ??

    TOM K8ERV Montrose Colo
  20. W5DXP

    W5DXP Ham Member QRZ Page

    On the contrary, my battery says "Marine" right on the case. It is designed to furnish 12 volts to the motor driving a boat's propeller (usually a small fishing boat).

    Absolutely false if the battery is being charged by 13.8 volts. Over the past 25 years of use, my batteries (with "Marine" written on the case) all have outlived their warranty periods when charged by 13.8 volts.
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