Battery Charger Design, It rained hard today, and I spent much of the day thinking about batteries and chargers.

Autozone Charger Display

Autozone Charger Display

This may be one of the better examples of why we need build products for those we expect to market to.  We best understand their needs and expectations BEFORE we put it on the shelf for sale.   

I may have woke up thinking about it, this is the time of year the temperature drops, but it’s also the time we have more electrical loads running, they arrive in the same time frame to challenge the chemistry inside the box under your hood.  The windshield wipers are on, the defrosters, perhaps the day is so dark and wet that you are running the head lights too. Some of us understand there are other things going on in the car, the fact that you have selected the defroster (defogger) option means that your Air Conditioning compressor is cycling, and you hear it click in and out, that electric clutch adds a little more..

It was last night.. my wife told me, “my car is cranking kind of slow and when I’m idling at a stop light in the drizzle and cold, the voltage meter ticks with a much wider swing.”

I’m lucky… my wife is the type to share these things, and it’s in contrast with the blonde down the street who drove all the way to Portland with the oil light on.

Yes, it’s that time of year when we throw heavy demand on a marginal battery, and some find themselves alongside a dark road waiting for a tow truck.

If the Alternator is old, it might be compromised itself, it’s possible that the brushes that provide power to the field are just not up to providing the full current necessary to sustain the large demand for more power with a bad or weak battery .  In some alternators there is built-in thermal protection and if the load becomes too great, the alternator will literally shut down until it cools off. If this happens with a compromised battery, it’s not likely you’ll restart the vehicle, and very likely that you will lose the ignition system before you figure the alternator is no longer doing anything to help you. The trouble can spill over.

So.. today I did buy a new battery for my Wife’s car.. and what a difference!

But.. I was still thinking about battery chargers and that different  “hands on’ review  of a small Battery charger using a High frequency Conversion Unit.  After buying the battery, I stopped by several Auto Parts discount stores and noticed that Autozone had a pretty good stock of battery chargers, I bought the one you see to the right, it delivers 10 amps, and yes, I did pay more to play today, this is very similar to the design reviewed I share.

The Author “Erica” is excited about this product, and I was first critical of her write up. She mentioned bringing a large battery to full charge in no time, and how powerful this little 6 amp battery charger is. We might guess that it’s about <=96 watts powerful, and we’d expect it to take a LONG Time x2 to charge a semi truck battery.

But Erica is likely deriving her information and satisfaction from the charger and the fact that the battery starts the car, garden tractor, or what have you when she’s done with the charger. AND the product has status lights on the front of it,  so when Erica says the battery is at full charge, it’s more than likely the light on front of the charger say it’s so.

She’s a very happy Customer, User, and Owner of a HF (smart) battery charger.

It took me a good long while to arrive at a place where I have nothing but respect for her effort to share her happiness with the product. At first I was expecting her to at least open the damned case and look around, or maybe slap a scope on it and look at the power conversion stage, or put a friggen volt meter across the battery and tell us what she saw.  Fact is, I’ve been exposed to Jeri Ellsworth, and some how I’m holding onto this unrealistic idea that every woman should know to bake her own Semi Conductors, and bend and weld metal too 🙂  If I criticise Erica’s effort .. I need  criticise my own, because I don’t always lay out the data during my rants or praise for a product.

Maybe I better share that my interest at this point is in the Product Design, as I said, the technology is good, and in fact, we won’t see the old stuff again due to the high price of commodities and the fact that efficiency in the older chargers was normally poor. A great big old inductor like that found in an old, heavy, reliable Xantrax inverter is NOT an efficient way to float a battery bank off AC… The power factor at float is something terrible. the HF Conversion design is likely the correct tool for efficient battery float.

So…here’s where we guess about this product and the design team who built it…

Maybe we ask who designed the product? Sometimes it’s the vendors of chips and other components, they sell this stuff with good circuits notes, and even examples of viable products 🙂 What it often turns out to be is a product designed by Engineers for Engineers.

I was curious about Erica is she typical of other users and owners of this battery charger?  I decided to look at Amazon for reviews of this product and others made by the same manufacturer. the result of my little study was a bit of a surprise.. it seems that nearly half the reviews there are from less than satisfied people, and some are down right pissed off about their experience.  This may be the time to mention this product has a five year warranty, that’s pretty impressive I think, especially if they really back it up.

There are no doubts in my mind that high frequency conversion is here to stay in battery charger design, and it has a lot of advantages, so how did this product miss the mark with half those who purchased it and made the effort to review it?

Here’s one reviewer that is not thrilled..  I found others that didn’t like this sc600 model, and it may have some design problems, or perhaps it’s features the reviewers had no appreciation for ?

Warning, don’t expect this charger to work when you need it most!

I purchased this for the very rare occasion when my wife or I accidently leave
something on in one of our garaged vehicles and come back later to find a
battery completely dead.

Such was the case this week when we left the key in the minivan with the accessory power running the fan and video player. Two days later we discovered the batter was completely dead. I opened the recently purchased charger for the first time, hooked it up just to discover it would not maintain a continuous charge. I called the manufacturer support line and they walked me through several tests and confirmed the charger was not acting properly, however, they refused to admit the charger was defective, and
rather, repeatedly asserted that my van battery was defective and needed
replaced! Of course, I found this a bit implausible since the premium high CCA
van battery was only 1 month old. I quickly dispelled the manufacturer’s
assertion and proved my new van battery was fine, when I borrowed my neighbor’s
charger which worked perfectly, and within a short period, the van started up
with no hesitation. I did some more testing and found this charger will work if
your battery is not dead and already has a charge, but of course, that is not
what I need a battery charger for! Fortunately, the product was still
within the return period. I plan to purchase a different charger.

Ok, let’s analyze his requirement:

He has a dead 12 volt battery (approximately 99.9 percent plus of all car battereis are 12 volt right? so this should make him part of the PRIME target audiance? I think so.

Let’s jump back to the design, this battery charger model works with 6 volt and 12 volt batteries, it does that because it can! but maybe it’s even better than that, the Engineers designed it smart enough to figure six volt or twelve volt mode all on its own! under processor control, is that right?

So how does this thing work? you plug it into power, attach the battery, the charger processor reads the battery and determines if it’s a 12 volt or a six volt, and proceeds to test and then charge it..

sooo… how does the processor know it’s six volt or 12 volt >IF< the battery is dead ?? I think the answer is it can’t, and if it sees let’sd say 5 volts, it must assume it’s a six volt battery. Of course if it came out of a guys Mini van who left soem load on for days, it might well read 5 volts or less!

We could ask ourselves if this is a Kiss design, but hey, we already know it’s not.. but maybe worse that that, it wasn’t designed to charge a dead battery either, and it appears that’s a pretty common expectation among people who shop for battery chargers.

If only we were sitting in on the design team meetings, what a great article that would make… all those drawings on the board, the excitement of designing that High frequency section and assurign you didn’t make a transmitter that totally knocked out all the communications between planes and ground at the local air port. Whether to put a fan in there or to spend the money on a big chunk of aluminum sheet and come up with a design that might cool when left running under some winter coat tossed on top of it.

Sure.. you know the public can be a pain in the ass, but wouldn’t it have been a great idea to collect some information from potential users of battery chargers and designed what they wanted to buy?

If you have spent time in junk stores, or stopped by garage sales to look at guy stuff, you might remember the battery chargers there for sale. Top four things that put them in the discard pile are:

  • Faulty Switches
  • Bad diodes
  • Frayed or damaged cords, plugs, or battery clips
  • Broken Amp Meter

We know all experienced engineers will look at these areas and design well enough to clear the warranty period..

Maybe the design team considered a way of selecting six or 12 volts with a button or switch, and possibly an led or two to showthe selected state?  But perhaps they just locked onto the fact they could have that figured via the micro processor, so why bother giving the user more control?

We’ll likely never know, as the book or article would never been as exciting as the stories told about Duntov, Delorean, and others during the golden days of designing stuff that people wanted to buy! We all watched as years went by and all the lessons learned seemed to have been forgotten, you need build stuff people want.

Here’s some additional information about HF conversion in battery charger designs.. it’s likely here to stay.

In this article about HF Conversion, if you know me at all, you can imagine the smile that came over my face when I saw this formula

Efficiency =  Output Watts/Input Watts

Since the authors of this paper also mention EVs, I think it’s worth mentioning again what kind of day it was here. Wet is not the word for it.. sop and wet might be a start, but we do have a lot of days like this, and watching the loads on your automobile’s electrics is quite telling. The wipers dragging over so much glass, and doing so in backed up traffic for long periods. The fan motor whirling, and sometimes a need to start that thermal resistance rear window defogger, to assure you can see to the rear and not cut somebody off while passing.

We note these things, and then think of the BTUs necessary to heat the cabin air, and keep all this cabin glass clear. If it were an ev we were driving, we’d be sucking the life out of the battery at a dead stop, we’s inch along in the heavy traffic going no where with very significant loads.

In the mind of an EV owner is the idea that EVs use near no energy at all crawling along.. rational people know that it’s either too hot, or too cold much of the time, and it’s just not so.

All the best,














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2 Responses to Battery Charger Design, It rained hard today, and I spent much of the day thinking about batteries and chargers.

  1. Bill Arenburg says:

    Reading the recent posts about smart chargers reminded me to check on my stan-by generator. The 0ne month old battery was attached to a Schumacher SEM1562A battery charger maintainer. One would think that I’d be ready to go for months to come. Reality tells a different story, push the button and all you hear is click, click, click. A little checking confirmed a dry battery, No Water in sight. A little more checking showed 16.2 volts at the battery terminals. Apparently my little “Microprocessor controlled” charger was not so well controlled after all. A lesson for all of us should be “Trust but Verify”. AND KISS. At least Walmart will get the chance to eat the battery and the charger………….

    • George B. says:


      Thank you very much for your post, I have been experimenting with this SC1000A model, and it seems to be far less smart than I had hoped. The power conversion section looks fairly efficient, the control of float voltage not to my liking.
      I think our smaller generator sets might do well with AGMs for start batteries, but some of these batteries >should< be floated at around 2.27 per cell or about 13.62 volts, exceed that and you will likely get less service than what you should. Batteries are expensive, and I expect our dollar will not fair all that well against commodities like lead in the future, so we need look at solutions that will actually look after our batteries. The answer is likely a programable charger where we can set the precise float voltage. AGMs can't tolerate high charge rates, or hight float voltages period! Bill, maybe we add our own float function using an LM317 VR or similiar, and an adjustment to float at precisely what we need. I am still dumbfounded that a manufacturer like this one would advertise that their unit could be used to flaot an AGM, and then float it high.. or float any battery higher than reccomended. I just went through the manual for this unit and it says it will 'float' the battery after it's charged.. I guess they didn't say they'd float it properly did they? It's just not that hard or expensive to make it right.. the power conversion electronics looks good to me, maybe this is a product we need to consider.... supplying a smart enough charger or offering an easy to apply modification kit for this one? The reverse engineering of the EM784 processor found in here can't be that tough, I don't know if they offer a repair manual or drawings for these, maybe? that might save an hour or two..

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