ShopTalk Sunday: The DIY Battery Charger

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Prepping note: The battery on the old Kubota is on its last legs.

It’s a 51-R series, and they ain’t cheap.  So, I was trying to get the maximum possible service life out of it.  Put it on an 8-amp charger and then got into some pulse charging on top of that…

Even after 2 days of pulse charging, I wasn’t sure of what was going on because I’d dropped the tractor hood too fast.  And OLED displays are not especially fond of that:

Which makes that one unusable.

So far, the winning “farm battery charger” is an old Sears/Craftsman unit that’s been around since 2004.  It works and it will even start the tractor, battery or not.

Second place used to belong to a Schumacher charger, but after serial charging of a battery that one literally overheated and smoked a bit.  So, roll-my-own charger went on the project list as a possible fixit project.

As usual, though, this kind of mass-produced unit is not “repairman friendly.”  And given that U.S. imports from Asia are beginning to crater [see L.A. (-41.19%) and Long Beach (-34.7%) cargo disasters in progress] we – ‘Merica – as a “shining light Beacon of Freedom to the World – are in a world of poo.

Because not only is Freedom of Speech between a rock and a hard place, but so is User Maintainable Anything.

My battery charger experiences recently have made it clear.  I need to “go deep” on some of the farm equipment that is most likely to fail.  So, another one of the small 8-Amp with pulse charging units has been ordered from Amazon for under $25.00.

Now I’ve gone one step further.  I’m going to whip up my own battery charger which ought to give reasonable performance at the modest price of having to pay attention to what I’m doing.

George’s Battery Expertise

Once upon a time, down the resume a way, I was head of sales and marketing for a company called Cruising Equipment in Seattle.  The outfit made dandy kilowatt-hour integrating microprocessor-based DC power instrumentation.  They also make multiple-stage charge controllers, as well.  In short, what I’m going to tell you can be taken to the bank.

Batteries have Input requirements (that is, charging) along with Output requirements (discharging). Do either one wrong or disappointment will appear.

Battery Capacity and Discharge Profiles

For our discussion, we will use a “generic” battery which might look suspiciously like a Trojan T-105 6-volt battery.  Now, turn to the spec sheet over here and scroll to the charts top of page two.

The one on the left presents a logarithmic chart explaining how “effective battery capacity declines as a logarithmic rate as the rate of discharge increases.”  Notice in this chart you can withdraw 100 amps for 100 minutes.  But as the rate of discharge increases, capacity drops.  Such that at 200 amp discharge rates you will get about 20-minutes (or less) of discharge rate.

Depending on market, batteries are rated at their cycling depth of discharge rate.  Forklift batteries tend to us the 6-hour rate.  The T-105 generalizes at the 20-hour rate as do most other consumer-oriented batteries.

What’s more, there is a cycle-life every battery has.  And if you regularly use no more than 50 – 60 percent of a battery’s capacity, its “cycling life” will be generally in the thousands of cycles.  Particularly if you perform periodic conditioning (“EQUALIZING”) charging.

There’s a trade-off between lead-acid and newer technologies like LiFePO4.  This latter is a lithium battery.  It cycles better, has higher power density, and can be deeply discharged to near zero without killing cycle life.  Stays in the thousands.  But there’s a tradeoff.  Besides a LOT more money? Very temperature sensitive.  Like disconnect chargers when you get to freezing and don’t charge at any more than about 12.6 volts.

Higher current under load (motor starting or running a microwave at the deer camp).  But LiFePO4’s will beat the shit out of your wallet.  I love Trojan T-105 style batteries (golf carts) because they deeply cycle well, and while they require some maintenance (periodic watering and equalizing) in our Solar operation here, we get 8-10 years out of a set of 16-batteries of the golf cart type.

Charging Parameters

There are four “stages” to battery charging:

  1. Bulk Charging: This is when your source (alternator, charger, or genset) is putting out all it can.  For consumer chargers the bulk limit for small chargers is in the10-30 Amp range.  Once you get to the $90 class charger, bulk charging at the “Starting level” shows up.  For liquid cells, battery size in Amp-Hours approximates the “economic” maximum source that’s useable.  E.G. for a single 100-Amp-Hour battery, more than a 100-amp alternator may be inefficient.  At this level, the battery may be as low as 10.6 volts, or so, on a deeply discharged system.  As the Bulk charging process goes along, the voltage will slowly rise.
  2. Acceptance Charging: This phase is also called Bulk Charging by some manufacturers (like Trojan).  Essentially, after running flat out to bulk energy into a battery, you get to a limit of “acceptance” above which the battery may be driven into gassing.  (“Boiling” isn’t correct, since electricity is breaking down hydrogen and oxygen and blowing off (highly explosive!) Brown’s Gas.  Charge liquid cells any harder than this and you risk inadvertently gassing the cells which increases water use.  Once a charger is operating at less than its ultimate output current limit AND the Bulk/Acceptance charge voltage is hit, you can set a timer.  Because the battery CURRENT will slowly decline at this constant charging level until current is at (or below) 1 percent of stated capacity. Takes 2 1/2 to to 3 1/2 hours on the close. For a 100-Amp-Hour battery, this means when charge current is less than one amp and the voltage is still 14.82 volts (around 60-70F!) you can dump in more energy forever but you won’t get any return on your investment.  Electrochemistry tops out.

I’ll direct you to the first page of the T-105 spec sheet next.  For there, you will see recommended charging voltages for the general type.  Pay attention to the voltages because when using liquid cells, they are important.

Source Trojan Battery spec sheet retrieved 4823
  • Floating Charge: This is not “charging” in the pure sense of the word.  Yes, you are putting some energy into cells, but only to the extent necessary to keep them “topped up.” Holding voltage.

Temperature Matters

All of these voltage measurements are referenced around room temperature.  When it gets cold?  The Acceptance Charge can move up to 15.5 volts on a nominal 12-volt system around freezing outside.  On the other hand, if you’re in Phoenix, 12.8-volts may be pushing it.

Charger-Gaming

One of my Schumacher chargers is toast (over heated, over-used), but a smaller one used all winter in the lean-to greenhouse did OK, though it did experience a couple of overvoltage conditions which dropped the diesel heater offline.

For now, I’ve got this still working charger, and the old-time Sears unit, plus the new pulse charger, so we should be good.

What I’m doing now, though, is sketching out a “George Made” unit that will arise from this pile of parts.  Pay attention and I will walk you around the design concept clockwise starting with the silver big power supply box on the left here:

  • The basic power supply does 10 Amps and has a built-in voltage controller. It will go all the way up to 48-volts. Amazon $40.
  • There are two voltmeters shown, but only one of them will be used,  Likely the one with the Hall Effect transducer (white donut and wires) because that will give me voltage and current information since I’m making a totally manual unit. Amazon price $21.59.
  • The BoJack box has a few capacitors (2200 uf 25V) because I like really clean D.C.  If you plan on using this on 24V or higher systems, increase the capacitors to 100 volt types.  Amazon $6.99.  I’ll series two of them to get to 50-volts which will get me into 10 amps at 24 volts, no sweat.
  • A power switch is needed – and I might go so far as to use one of the Double Pole, Single Throw (DPST) types so I can get the A.C. line completely disconnected from the unit.

The next part of this project will be going through the “designer part.”  Which is where I look at airflow, consider insulation, where the AC wire comes in, where the charging wires will come out.  Banana jacks, red and black?  Hmm…

Then it’s a matter of sitting down in front of TinkerCad.com with a digital caliper and drawing up the enclosure.  With the 3D printer, I can draw the perfectly aligned square meter cutout and the ideally positioned with holes and cable gland holes just exactly where I want them.

In the end, I figure the out of pocket will be around $85-90 bucks.  Which is up in “another Schumacher” in terms of price.  But on the backside of an uncertain future that MIGHT include wonky grid and microprocessors in collapse, this semi-analog approach might be useful in situations most people will never encounter.

For one, since it is infinitely adjustable, I could put a couple of LiFePO4 batteries in the 100 Amp-hour range in parallel and use that to power the solid-state ham gear. Or be a little “stiffer” supply for the electronics bench.  (Though honestly, I seldom get anywhere near the 3-amp capacity of two power supplies there.

Notwithstanding, there are many things to consider here, not the least of which is the bragging rights and having a microprocessor-free power supply for whatever moves me.

Not the Last Supper

Thanks to the ham radio crew on 3806 this morning for a fine discussion of how to make perfect beef brisket.  We’ll be trying the ideas out this afternoon and to go with it, I’ll be doing a batch of our family’s spin on Cuban bread.

Toss in 16-ounces of cheapo jug wine and we will have zero risk of wasting away out here in the woods.

Write when you get rich, or a light bulb comes on…

George@Ure.net   (and Happy Easter!  Which reminds me to go find the bunny now…)

34 thoughts on “ShopTalk Sunday: The DIY Battery Charger”

  1. Played with chargers for years with varying success. Spent $A300 brought the 30amp smart charger, 8 stages that ( supposedly ) reads the battery type and charging rate. Its worked quite well to be fair.

  3. ATL: home “improvement” project keeps starting / stopping. We (me anyway) are growing weary of various contractors failure to finish. Spam hits the fan next week.

    I brought battery #1 out of the cold to spin up tractor #1 and mow yesterday. Now the (6) forklift golf cart batteries are on charge overnight. Next comes tractor #2 then … the pontoon boat. I have three chargers, one from the late 90s.

    Crawdads are coming out and I saw a bass yearling this morning. Must be spring! Happy Bunny Day alles,

    Egor

  4. George
    Happy Easter to you and Ure family!

    So back in July 2022 I commented about using a soft starter on air conditioning units to reduce compressor inrush current. I had purchased a Micro-Air device and intended to install it.
    The decision was made to hold off on that until cooler weather came. The thinking was that it could not be chanced that a failure of our air conditioner would put She Who Must Be Obeyed in a dangerous situation.
    A high heat situation could be fatal to her!
    So last Monday it was decided it was time to do surgery on our 8 year old AC unit. In addition to adding the soft starter a new control board and temp sensors would be installed. The AC unit had started to not cycle correctly at the end of last summer.
    OK, I get the beast pulled out of it’s case and onto a stack of concrete block. I start looking for the compressor run capacitor so I can discharge it to ground. That is a mandatory safety step!!!!!
    Where’s the damn capacitor? It’s usually mounted near the compressor and easy to get at.
    Not so on this AC unit by Frigidaire. It’s hidden inside an enclosure under the control board enclosure. You must disassemble the fan shroud just to get at the capacitor!
    No way! Not that day!
    It was decided to install the new control board and temp sensors and leave the soft starter for another day. The run capacitor was discharged by touching a grounded wire to the hot terminal on the control board.
    This repair solved the AC cycling problem.
    It was decided that we would wait on installing the soft starter until we buy a new AC unit to act as a spare. It’s too risky for my Ladies health to be without air conditioning.
    I will also buy a sheet metal nibbler so I can get at that run capacitor without taking the front of the old AC unit apart. This is required to install a soft starter. Where there’s a will there’s a way!
    It appears that the lawyers and safety engineers at Frigidaire don’t want you to fix it yourself. Just call an a repairman or better yet buy a new one.
    I fully intend to install the soft starter on the old AC unit. This is so I can run that unit from a portable generator. I just have to do it in such a way so that my Lady’s health is not put in a risky situation.
    The saga continues, stay tuned!

    • I bought one of those soft starters for our air.. thank you very much.. what a change in usasge..

  5. Happy Easter! Re: batteries and eternal life — I have my Dad’s calculator made in China by Royal Ideas, HK Design Reg. No. 01106703.M001. Dad passed away in 1993 and I don’t know exactly when he got the calculator but the darn thing is still running and has never had a battery change! It does have a battery compartment. At the top of the front is a small oval window with what looks like a tiny solar panel. The calculator is usually in a drawer when I’m not using it so I don’t understand how it could be recharging somehow!

  6. “My battery charger experiences recently have made it clear. I need to “go deep” on some of the farm equipment that is most likely to fail. ”

    the reason you need to go deep.. is pretty much in the article below.. but my interpretation on why batteries don’t last as long.. is the business model.. things are made cheaper and charged more for.. batteries either in jell or acid bath.. the plates are not a thick as they use to.. the cost of lead is high.. the boss’s car is a hybrid.. electric.. for fifty miles the car only runs on the battery.. will start the motor up if you gun it or go up a steep incline .. the distance you get from it varies on how you use it.. I get around fifty miles to a charge the boss gets thirty ish.. the kids get twenty ish..
    now the twelve volt battery that runs the radio etc.. we were noticing that they fail quite often.. in visiting with a tech.. his response was yes you need to drive it further.. huh.. yup the motor is what charges it.. I thought it was integrated into the charge port.. nope.. so I put on a battery maintainer..it has been three years now.. plug it in when you park it.. all the cars have them.. because of the vampire power usage takes down the length of a battery along with cold and none use.
    the twelve volt battery made for the prime is three hundred plus install.. everywhere else.. I suggest to the kids to get industrial batteries.. they have the bigger plates.. of course the price of lead is almost as good as gold so the cost is higher..
    https://www.bigtimebattery.com/store/Trojan-J185E-AC-replacement-battery.html?gclid=EAIaIQobChMIxMffo4ad_gIVnhGtBh30HwOpEAQYASABEgL48vD_BwE
    where today we go thinner and keep the price the same or go up accordingly..
    for the average you and me.. the battery only has to last one to two years..

    https://www.wheels.ca/news/car-batteries-aint-what-they-used-to-be

  7. i have small, 15-20w, 18v solar panels mounted on two tractors and a pickup. connected directly to the battery. No regulator. Batteries last a long time.

  8. Now I was considering making a twelve volt high voltage capacitor bank.. the issues is slow discharge or high discharge..

    https://www.droppinhzcaraudio.com/products/xs-power-sb1000-75-group-75-12v-super-capacitor-bank
    https://www.droppinhzcaraudio.com/products/xs-power-sb500-49-group-49-12v-super-capacitor-bank

    I am actually still considering that to for part of a battery storage for the new inverter that will be going up in the next few weeks.. twelve volts lifepo and twelve of high capacitor.. slow discharge.. I will do it one at a time.. though don’t have the cash to do it all at once..

  9. As the owner / user of an all electric voyager, on this beautiful Easter Day i thank you, George, and all the community for an endless amount of useful information.
    And i thank the Dude every day that if all else fails, i have sails. Multi thousand year tech that was IT long before we discovered explosions could be harnessed.
    Wind’s good for everything but windmills.
    Stiks

  13. I went with an agm battery for simplicity of charging. lifepo4 batteries depend on internal complicated electronics to protect themselves – just one more source for failure imo. Also one more thing to try to remember about taking care of them differently than other batteries.
    I bought one of these and it seems to have saved a weakening car battery as well as keep my other seldom used vehicles charged up. It only uses about 1 amp so it takes a day or longer to charge.
    https://www.amazon.com/Battery-Maintainer-Portable-Motorcycle-Batteries/dp/B07CZ7KWP3/ref=psdc_15719911_t2_B073Z73TB5
    This runs a 4 stage charge cycle and seems to be idiot proof. I like it so much that I bought a larger version for the diesel heater. The best advice I found was to run a desulfate/charge cycle about once a month.

    • I put maintainers on all my cars.. Best twenty bucks you’ll ever spend..
      as cheap as their making batteries today you’ll save e many times the cost of the maintainer

  14. Happy Easter.. did you see the MSM lineup..
    Historically.. they would show such movies as the robe.. or a series of religious shows.. today..
    we have the whole series of Friday the 13th.. and a few zombie apocalypse type movies… nothing at all associated with a holy holiday…
    The boss was looking and said what in the heck is this.. I said two years ago and five months the world flipped over.. did you expect less..

  15. not to mention the lets hack sally and rape suzie movies.. I didn’t see one show that was associated with a religious holiday at all..

  16. “Because not only is Freedom of Speech between a rock and a hard place, but so is User Maintainable Anything.”

    On the road leading to the dump, there is a flatscreen TV nailed to the post with the screen painted as a sign: TV Repairs. (Phone No.). I thought to myself “Who even TRIES to fix a flatscreen now days? Might be a replaceable power supply brick, but as for screen problem? That micro stuff is just not fixable. I wonder how much business he gets.

    I have a bench power supply that reads me voltage and current that I used to Equalize a near-dead battery that a friend donated. Manually watching voltage and current. Amazing to watch the current decrease to near nothing when the battery is ‘well done’. Battery still in use on my offline solar system for the hot water pump & controller.

    And I built myself a ‘Ham Can’ battery into an ammo can for the ham radios. Two LiFePO4 rated 256 watt/hours each. Total ‘half-kilowatt/hour’ box with various output connectors, USB, Cig Lighter, & banana posts for the battery. Small A/C charger module fits inside the box. And I have a couple 50 watt PV panels in a fold-up carry along pack with a charge controller for the Lithium Iron battery. Yes, the batteries required a ‘walletectomy’ to pay for, but I figure I will be willing the battery to the next generation of user after I’m all worn out.

    • ” I wonder how much business he gets.”

      Probably quite a bit. You might lose a pixel or two, but LCDs and OLEDs are pretty much unbreakable (unless you’re a Hawaii-Hilo fan and keep a pile of bricks in the viewing room.) A modern TV goes south when its antenna or cable line is hit by lightning, or when the power supply shits itself — just like a computer. (I made a bit of money, replacing power supplies in, especially Dell and Compaq computers, because the factory would install a PS which was barely marginal.) I knew about the power supply issue when no one else seemed to, which I never shared, because I liked making $200 for four minutes of work, and figured that was a proper payment for having a Senior VoltOhmist, and knowing how to use it. I would even sometimes get boxes from other vendors.

      A n y w a y . . .

      George wrote a piece a few years ago on repairing the PS in a TV. When the flat-panel TV dies, the PS is almost always the issue, and it’s a quick enough repair that a body could make a living replacing them for $100 per, which is cheaper than buying a new set…

  17. Off Target, but it may be useful for some.
    My internet choices have been limited to AT&T (DSL) or Comcast/Xfinity, which I have used & paid extra to get their ‘High Speed” option. When they raised the price again, I went looking for an alternative. T-Mobile has just started offering 5G wireless Home Internet service in my area (Sacramento, CA). They offered high speed, no data limit service with a locked in $50/month fee. I tried it, and my Warships game runs seamlessly. They send you a wireless router, which was easy to set up.
    It is a solution for me, which with a Hulu subscription for my home TV, saves me about $60 a month.

  18. Off Topic, But may be of interest to some.
    My internet choices have been limited to AT&T (DSL) or Comcast/Xfinity, which I have used & paid extra to get their ‘High Speed” option. When they raised the price again, I went looking for an alternative. T-Mobile has just started offering 5G wireless Home Internet service in my area (Sacramento, CA). They offered high speed, no data limit service with a locked in $50/month fee. I tried it, and my Warships game runs seamlessly. They send you a wireless router, which was easy to set up.
    It is a solution for me, which with a Hulu subscription for my home TV, saves me about $60 a month.

    • Time to early Spring fertilize my garlic this week, I use triple 15 and just on the rows. Daffodils blooming, tulips soon.
      Planting potatoes this week.

  20. Couple more notes is that charger I mentioned automatically starts with desulfation and the 3 amp one I bought later has 2 selectable desulfation programs. For $20 it automaticly desulfates, does 2 stage charge and then maintains charge for however many months you leave it connected without overcharging. One thing I came across while researching battery charging for weak batteries was to try several different desulfaters in addition to making sure liquid levels are over the plates. I was always careless about liquid levels until the $200 jab that a new battery now costs.

    So the wife’s 11 year old toyota is still running on the original battery while I’m out $200+ for replacing a 7 year battery after 5 years of use. That is what motivated me to spend a few days researching. When her battery started getting weak a couple years ago I started messing with the desulfaters and now it is not like new, but it held a charge for 5 days in an airport parking lot in north Minnesota.

    The punch line is that car manufacturers could throw in a cheap little box of electronics to double +/- the life of the (lead/acid) battery for their customers but they don’t give a damn.

    • “car manufacturers could throw in a cheap little box of electronics to double +/- the life of the (lead/acid) battery for their customers but they don’t give a damn.”

      That’s silly — of course they do. They care about making payroll.

      Once upon a time, manufacturers cared about longevity. That was when $1.50/hr was more than a living wage, and they had to convince people to spend eight months’ wages on a motor vehicle. Any argument they could use, to convince John Q to buy a Chevy instead of a Plymouth, or a Mercury instead of a Buick, was a viable sales point.

      That was then, this is now, and anything the stealer can do to get a car inside their garage, will be done…

  21. pps, the new chargers can be shorted, wired backwards, left for months connected forgotten about no big deal and your battery will be in great shape when you need it. Bar is set high for your diy charger.

  22. Dude: js is totally messing up yer site!
    posts lost
    malfunction with some sort of loop when js enabled
    if i bother to post, i usually copy, gone soon
    everybody will miss my brilliant insights (u;no thats a joke rite?)
    btw, insets appear as ugly blue rectangles

  23. I have an Associated battery charger ( https://www.amazon.com/dp/B000IOAWW4 — not this one, but one model cheaper. They no longer make mine and this is the closest to its spec…) which is American-made and waterproof. It’s also a bigassed transformer — no actual electronics — so it’s bulletproof.

    I’ve got a couple “intelligent, pulse” chargers for remediating dead batteries, but the small one is a Harbor Fright which is worthless. I don’t plan on building anything, because that Associated is probably bulletproof (and it was, like, $300 direct from Associated.)

    Who says you can’t buy American…?

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