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. 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.

    Joe
     
  2. 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.
     
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum 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.

    WB2WIK/6
     
  4. 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.
     
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum 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?
     
  6. 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
     
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum 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.

    WB2WIK/6
     
  8. 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
  9. K8ERV

    K8ERV QRZ 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
     
  10. 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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