Kmart battery charger... hmmmm...?

Pulse charging is used to put maximal charge charge into a battery in Float Mode - CTek chargers do this.

Mike

I know some do it , arguable value , but not the current issue.

Just being sure , that it doesn't pulse under some conditions
for example in 1st part of cycle only and maybe meter read 16V then acorss terminals.

If genuine 16V1 at battery terminals under load and not something funny like different input volts setting (unlikely) then its to much.

Robin Miller

Max

Have a look at the prices of the equipment on your companies web site. There are no cheapies like the one being discussed. There are plenty around so if they were good, reliable and would produce repeatable performance your company would stock them.

PeterD

Sorry about misplacing that last reply - it should have gone into the follow ups on the next message.

PeterD

you're exactly right, Peter. I just didn't want to say it ;) We don't like to stock unreliable products, because if we did we'd have to deal with complaints and returns.

Max

Even Deep Cycle gel-cells can be recharged at 20% of the Ah capacity.

Mike

I think gel batteries can by cycled much harder than other types of deep-cycle batteries. Sure batteries can be recharged at 10%, but to get maximum life out of your batteries you should recharge at 10%.

Max

i mean ..."sure deep-cycle batteries can be recharged at **20%** .. but to get maximum life out of them you should charge at 10%"

Max

Mike

If looking for pulse charging , it isn't normally invoked when suppling full current ,ie when it starts charging , as the pass transistor is usually fully on.
It gets progressively more "Pulsy" (is that a word) as current drops off but before it drops right back, and usually no pulse when in holding pattern.

Robin Miller

Mike

Why do you confuse us mere mortals changing from volts to amps

"I had it set at 2 amps to charge the 11amphour gelcell. It charged at 2.3 amps initially (Stage 1) then reduced current holding 14.1 volts (Stage 2). "

Is the 6 amp unit designed to charge a small battery?

Bill F

Mine behaves the same Mike, the packaging it came in was nice though.

"Why do you confuse us mere mortals changing from volts to amps "

- because that's how 3-stage chargers work.

Stage 1 - constant current
Stage 2 - constant voltage usually 14.4
Stage 3 - constant voltage usually 13.6

Mike

Hi Eddy

Not a test :)

I may well do a more detailed analysis of the charger but as it is a multi stage and multi mode charger it’s control sequences may take many hours to cycle through and that means I’ll have to (at the least) data log the voltage for quite a while. I was just hoping that someone may already have done, at least some of, the work for me :)

Despite people paying silly money for them a battery charger is not a complex piece of technology; a switch mode power supply of about 150W, a switching transistor or two and a microcontroller with an analogue to digital converter, write a bit of embedded software and you’ve got a high rate multi stage battery charger. Even the code isn’t complex because everything happens so slowly and, iirc, companies like Maxim publish algorithms for it.

It may well be that the Kmart charger is working correctly and I simply haven’t allowed it enough time to complete it’s cycles. But as I’m going bush for a few days on Sunday I’m a bit tight on time however I will have a more detailed look at it and report back.

Mike Harding

One thing for sure Mike.
The battery will be well and truly charged on your return from the trip!
Have a good one and don't forget the trip report for all of us less fortunate souls!

Not much of a trip I'm afraid, just off into some rough country to do a few days gold prospecting but I love being out in the bush where ever it is :)

Hi Mike. I also look forward to the answer to your post.
I have a Ctek, but my camping mate bought one of the Kmart units.
My initial test on his unit produced almost exactly the same results you measured. My best guess is the algorithm's wrong.
If the chip is in a socket, rather than soldered in, you could have some entertainment next Saturday afternoon. A bit of code and an EEPROM.
How do you feel about contracting to Kmart? Could be a market for you!!
( ok - it was just a thought - happy prospecting...).

regards............................Keith

Why?

As I mentioned above; a battery charger is a pretty simple piece of technology and if they've got the software right it's a cheap charger and if they haven't Kmart will refund my money without an issue. I win either way.

Mike Harding

Sure but what about the honest, hard-working people that don't own an oscilloscope and cook a $300 battery. K-mart won't pay for it and the battery warranty will be void.

I appreciate your input on the forum and you are well versed in DC current. Let us know what you find / work out.

CTEK chargers are a LOT more expensive - but there have been at least two posts of faulty ones blowing up batteries.

Mike

"if they've got the software right"

- the Jaycar $99 3-stage charger doesn't even use processor chip because you don't need it. It's just a current limited constant voltage supply, where the output voltage switches between two levels based on current level.

When the current is greater than Imax/10, Vout=14.4, when the current is less than Imax/10, Vout=13.6.

Mike

I don't think the jaycar is a three stage..............they use the term two stage. I have one.

>the Jaycar $99 3-stage charger doesn't even use processor chip

No reason not to do it that way for simple battery charging, years ago I did an alarm control panel using the same technique. But given that a small 8 bit micro comes in at about $1 or less these days it provides a lot more flexibility.

I haven't taken it apart yet (but will :) however the manual, in big letters on it's front cover, says "Fully automatic microprocessor controlled battery charger" and looking at it's process cycle and front panel controls I would be pretty sure it does have one. A micro would, probably, be the cheapest way to handle the job. This is for the Kmart model I-7012.

I'm tempted: :) to reverse engineer it, replace the micro with an 8 bit PIC and rewrite the software - that way I can have a fully personalised high current battery charger. However if I cost it at my standard hourly rate I'd probably be better off buying a couple of CTEKs :) Then again: I haven’t done any electronics just for _me_ for years! A bit like the plumber who never repairs his own dripping tap :)

Mike Harding

Mike - I'm looking at adding Pulse-Charging to my Jaycar MB3612 - it's toss-up between using a PICAXE or a 555 to determine the duty cycle to switch the output between Float and Absorption voltage !.

Mike

Brewman - the reason I know the Jaycar $99 is a 3-stage charger is because I've measured the output.

The colours of the Power Light also confirm it -
Stage 1 - Red - current limiting
Stage 2 - Yellow - Absorption Voltage
Stage 3 - Green - Float Voltage.

Of course this must be the first time in history that marketers who wrote the promotional material left out a useful, working feature.

Mike

Hi Mike

The PICAXE uses a BASIC compiler I think? Ho Hum.... Probably quite straightforward to get going if you don't have a lot of embedded experience but it will limit the control you have and your code base will be larger. Consider downloading either the Hi-Tech freeby C compiler or the fully integrated package Microchip supplies and writing in either C or assembler. I think all the new FLASH PICs have a simple "in circuit programming" interface to the PC.

otoh a CMOS 7555 is simple and with a couple of pots in there you could easily change the M/S ratio but it's not as much FUN :) Anyway once you get a micro going you'll find all sorts of other things you never new you needed to do with it! :)

Drop me an e-mail if I can help.

Mike Harding

mike_harding@fastmail.fm

When I needed an interface between my Codan 9323 and Z100 Autotuner I used a PICAXE, because you don't have to write software lines, you create the flowchart using a free compiler, press the button and its in the PICAXE.

I have done it the traditional (hard) way for more challenging projects (PICAXE BASIC, Visual Basic, Z80 Assembler, 8080 Hex).

Mike

Mike DID

Think it's of marginal value anyway to make it into pulse charger- there is mixed
theoretical support for that type of operation and even then main reason is to
reduce overheating and other bad effects from fast charging (1C) .

With realistic <10amp most of time from Jaycar unit its unlikely to overheat battery.

Love the little Pixaxe's here , use them it several car projects , but the basic language they use is very simple and can't even support if then if stuff.

But where ever you want to measure a value/temperature or logic level or re-map and switch with it then they are great.

Robin Miller