Clamping equalization regulation?

[Madscientist267]

Hey guys -

With the advent of building the new charger for the offline backup, I have been pondering the ways for regulating the voltage during equalization.

I realize this will be a bit brief and lacking in detail, but I can't seem to find the info I'm looking for with the usual search terms in Google.

What I'm thinking is, an 'external' regulator made of nothing but mosfets and zeners. The charger's "equalization" mode turned out to be more of a "topper" mode because it can't quite get the battery up to 15V+ with the low side charge rate module. Rather than redesigning the whole charger, I came up with the afterthought of a provision to 'lock' it into high rate charge, which can easily drive the voltage WELL above anything even considered safe, nevermind equalization. Problem is, there's no active regulation in that mode. As it currently operates, it hits high charge rate and switches down to the low rate when a comparator gets tripped (at 14.4V).

So here's my proposition - The zeners would be set up in such a way that as the voltage at the terminals hits 15V (or so, maybe a little bit of provision for adjustment would be nice, say, 16V?), the gates on the mosfets would begin to kick in and waste the extra power through some homebrew nichrome resistors.

I have a suitable heatsink, and a few IRFZ (all same type, can't recall the actual part # ATM), but they can handle some decent juice with adequate sinking. The resistors would be in the neighborhood of 0.5R to 1R or so, and several of them, along with a fan to keep everything cool.

Sound plausible? I need a cheap solution here, I'm trying to stay away from anything either commercial (or complicated) due to cost. I've already put enough money into this thing that my wife is ready to hang me by the charging cables.

Thanks ahead of time,

Steve

[Hilltopgrange]

“Sound plausible? I need a cheap solution here, I'm trying to stay away from anything either commercial (or complicated) due to cost. I've already put enough money into this thing that my wife is ready to hang me by the charging cable”

Define Cheap?
I have played with many chargers both bought, built and scavenged some worked better  than others but all need a level of intelegence, human or electronic. I made a few simple attempts with electronics all proved to be unreliable but that was more to do with the builder (me) my most recent attempts used “confused logic”(me again) where I was present pushing buttons and sucking acid up a tube and prodding with a probe. Some of the hairbrain schemes I tried where downright dangerous AND NOT TO BE RECOMENDED.
Charging schemes that involve human intervention only work until you get distracted by a phone call or a pretty lady!   

All I was trying to achieve was to have the ability to charge or equalise my expensive batteries, I wanted it to be cheap, reliable,safe and able to work on its own without me and not need some edjit to remember to turn it off.

After 10 years I eventually threw some money at it and the problems all went away .
I bought a forklift charger made by Hawker Oldham the lifeplus model its totally automatic and has exceeded my expectations of it.
It was also in my opinion cheap as chips and I should have had one years ago. When comparing the costs of all the components that make up my wind & diesel generator system the charger is probably the cheapest one.
The charger cost me a mere £75 +£15 delivery used from ebay.
So not expensive by any means.

BTW if your wife is only threatening to hang you by the charger leads your not spending enough money! I get strung up by more than just charger leads at least once a week or whenever DHL arrive.
I find the phrase “I NEED” works much better than “I want” (mostly)

Russell


 

[Madscientist267]

Cheap as in almost no trips of the currency exchanging variety

Really, the charger works fine for everything else except the equalization. I gave new life an old UPS and built the entire thing from the ground up, and it does an excellent job, and even would do the equalization, albeit on a smaller battery (it's maintaining an 8D).

I gave it as much of a brain as a single LM339 can provide:

Charge rate based on terminal voltage w/ hysteresis

Thermal control for fans

Overload/overheat shutdown/cool/resume functionality

The 'EQ' mode (that has been re-purposed as the 'lets do the other 20% of the charge' instead of equalizing).

So my solution was to just redefine what it's functions were and for that it does well, because there's literally no space left inside the unit to add anything else; its going to have to be external.

I'd go with a dump controller, but I really want super simplistic, all 'analogue' (ie no PWM etc) in order to keep part count down, and I just happen to have a decent amount of shiny new nichrome wire that would serve the purpose well, as well as some scavenged TrenchMOS workhorses that love to carry juice.

The upper charge rate is fused at 25A, but with 15~16V at the terminals during EQ, it probably wouldn't be dropping more than 10A or so, so that's all I need to be able to dump...

Steve

[ghurd]

You really do not want to use the Zener type control with mosfets.
They will operate linear, meaning HOT.
And the voltage regulation will be too sloppy to work worth a hoot.

Pointing out the obvious:  Ghurd controller?
Cheap & easy, low parts count, and still has the speed of PWM (if you want it to).
G-

[Madscientist267]

G -

Actually, LOL yeah I did think of you when I was writing the last post... But couldn't remember which method you used in the design. Was at work and didn't have a whole lot of time to pull it up and look it over.

As I recall it seemed PWM, but how is the output stage set up? Can it just drive MOSFETs directly and subsequently into 1R or so loads? Im looking at one of two trannies for this - either IRFZ44N or IRFZ48V, both designed for pulsed application, but figured mega-heatsinking say 4 of them in parallel would distribute the heat a bit better since we're not talking insane amounts of power to waste here. I figure even linear, at ~2.5A a piece, they'd be ok.

Either way, if its cheap and easy, I'll give it a go.

LOL Just a tid-bit of trivia surrounding this whole thing haha - By 'easy' I was looking into even avoiding the use of a PCB if I could get away with it! 

Steve

[Madscientist267]

Well, I see I've managed to post the beginning of the thread in the wrong area... still getting used to the new board and where and what... so sue me LOL I only half way pay attention sometimes.

I looked it over, its basically a linear, but with a much sharper transition than directly zener -> gate driven response would be, right? In hind sight, should have just re-thought the fourth comparator in the 339 and hit it with that... LOL maybe rev 2. Hahaha yeah, well, about that - as soon as I get out of the dog house for building the first one haha

Still offering the kits for sale?

Steve
 

[Norm]

Still offering the kits for sale?

Steve
 

I am pretty sure he is .....
at least as long as he has this at the bottom of his postings
so easy to remember but i keep forgetting LOL !
 www.ghurd.info
Norm.

[ghurd]

The kit is still available.
And like Norm, I never remember that link is down there!

It is Not linear.
And it is Not bang-bang.

I like to think of it as PWM with a self adjusting frequency.

4 parallel fets will handle 1 ohm fine.  I think 3 would do it fine, but with a homemade resistor, 4 is probably a good idea.
I suggest each Gate have a balancing resistor to keep the fets switching more in time with each other.
I suggest the fets all be from the same production lot (from the same factory packaged tube).

The frequency was intentionally slowed down to keep the yellow LED on longer,
because if people could not see the Yellow LED blinking, they thought the circuit was not working.
The pics below show it with a lower value cap than is in the kit.

Medium duty cycle, with a medium charging current.


Higher duty cycle, with a higher charging current.



"with a much sharper transition than directly zener -> gate driven response would be"
Not a good idea.
A Zener driven fet Gate would have nothing sharp about it.
I kind of doubt the battery voltage could be controlled within a volt, and maybe not within 2V.
That type of thing would be better off using some big TO-3 bipolars, if you can find something suitable that costs less than a...?

G-

[Madscientist267]

Ok looks good. 3 questions:

1 - I don't really need any hysteresis for this application, all it needs to do is clamp down at a set voltage. Does RX need to be there as a pull-up, and if so, 470K-1M ok for it's value?

2 - What (if any) mods are needed for 15-16V threshold range on the pot?

3 - Which shipping method do you use (will determine which 'address' I give you)

Steve

[ghurd]

1-  RX does all kinds of things that are not apparent.
I do not suggest going any lower than about 220K, and that will run so fast you can't believe it.  With hysteresis, the circuit runs so fast and accurate a normal meter reads the battery voltage as rock solid stable to 1/100th of a volt, usually.
There is a 220K and a 1M in the kit, but the 1M is for other requirements (such as R5 in an LVD configuration).

2-  No changes required.

2A-  Do Not disconnect the battery from the charger and ghurd controller.
First disconnect the charger.  Then disconnect the ghurd controller.

3-  USPS.  Faster and cheaper.
But don't post your address!
Best do it through email.

G-

[Madscientist267]

Alrighty then... that brings up one more question (with a probably obvious answer) but I just want to make sure...

It makes a 'clean break' (ie 0% duty cycle) below threshold so as to not dump any power at all, correct? I'm looking to install it on a permanent level, and just want to make sure it wont pull any significant parasitic draw on the float, or if left connected with no charging input wont drain the battery, etc.

And how do we do payment?

Steve

[TomW]

Alrighty then... that brings up one more question (with a probably obvious answer) but I just want to make sure...

It makes a 'clean break' (ie 0% duty cycle) below threshold so as to not dump any power at all, correct? I'm looking to install it on a permanent level, and just want to make sure it wont pull any significant parasitic draw on the float, or if left connected with no charging input wont drain the battery, etc.

And how do we do payment?

Steve

Mine has no real "parasitic" draw, other than the LED that I ever noticed.

Glen accepts travelers checks, Paypal, Gold Bullion, Blood Diamonds or just plain old cash.

A couple guys manage to get them free, too.

He will work with you before and after the sale, too. This is rare these days for such an inexpensive device.

Tom

[ghurd]

What Tom said.

I sent a PM.
G-

[ghurd]

I suppose I should answer the other questions too.

Yes.  Clean break.  No dumping if the battery voltage is below the set point.

Parasitic draw.  Depends on the configuration, and the set point.
Typically, when built as a dump load controller, uses about 5.2ma, of which about 3.2ma is in the Green LED.
Could drop that a tiny bit by using 3.9K instead of 3.3K for the Green LED resistor R1, and there is a 3.9K in the kit too (ain't that handy?).
Could drop it a smidgen more with RX as 150K or 180K (both of which are also in the kit, go figure).
I don't think it can go much below 5ma, so its mostly academic discussion.

I would venture a guess that almost all 'ghurd controllers' are permanently connected 24/7/365.
G-

PS-  While we are at it, a pic of Low Duty Cycle for good measure.

[Madscientist267]

LMAO Sounds like a winner... hahah to me, at this point, anything less than about 50mA is below 'parasitic' (the sense circuit in the charger itself draws that much when in "ain't nothin happening here" mode).

Okie. Lets do this... Im gonna get like 2 or 3 of them. Pile me up on the 44N's too, at whatever the cost, I'm a bit low on stock 

Checking the PM right after submitting.

Thanks again guys. Im sure this will work nicely, and even if OTB doesnt do exactly what I need, Im not afraid to play with it. Just wanted to know what all I was getting into.

Figured I'd post one more Q here, since someone else might find the answer useful;

When configured as LVD, is it just best to have it drive a relay/contactor?

Steve

[ghurd]

"When configured as LVD, is it just best to have it drive a relay/contactor?"
Not usually.
A car relay uses like 220ma.  5.25AH per day.
A better relay maybe uses 80ma.  2AH per day.
(if a relay is required for some reason, there are tricks to reduce what they use)

A fet uses '0'AH per day.
G-