Fechter's Mini Meanwell Limiter Board

[cor]

If you connect pin 5 (+ input of 2nd Opamp) to the OVP point (which is always 2.5V) then you do not need to split the 160k resistor in two, saving one more resistor.

[teklektik]

!

[fechter]

If you connect pin 5 (+ input of 2nd Opamp) to the OVP point (which is always 2.5V) then you do not need to split the 160k resistor in two, saving one more resistor.

We think alike! I think the OVP point will work to feed the op amp, thus saving a resistor.

It's possible that could induce some kind of oscillation when HVC activates but even if it did, I don't think it would cause a problem.

Going back a few schematics to cor's, it would be possible to use a single un-isolated CellLog by placing a diode (LED?) across the HVC pins and programming the CellLog alarm to be normally closed instead of normall open. The alarm line would then pull the line to ground during normal operation and the resistor would pull it up upon alarming. This would have the added benefit of being fail-safe on the alarm line wires. If a connection goes open, it would terminate charge.

I do like having a separate LED for indicating HVC versus limiting. It's bad practice to reverse bias the LEDs though, I'll have to check the reverse voltage rating. I've damaged them with reverse voltage before.

[teklektik]

... It's bad practice to reverse bias the LEDs though, I'll have to check the reverse voltage rating.

hmmm - I've cooked a few doing that as well - I think LEDs are commonly rated at Vr = 5v so this doesn't look good with reverse 12v... too bad - I kind of liked the HVC indicator.

[teklektik]

... and programming the CellLog alarm to be normally closed instead of normally open.

Maybe I missed it, but I don't see a way to directly configure the CellLog alarm for NC operation. Are you thinking of pressing the CellLog LVC setting into service as a NC HVC?

[fechter]

I'll have to double check the instructions but I'm pretty sure there is a setting for NC alarm output.

[teklektik]

fechter - One last try to get CellLog direct connect compatibility and an HVC indicator - this time with a 2-lead bicolor LED to circumvent the high Vr issue. The red HVC indication relies on U2/7 going high to suppress the charge current causing U2/1 to fall to Gnd. U2/1 and U2/7 have the reverse relationship during normal limiting operation giving a green indication.

mini limiter board schematic 3a-5.jpg (38.7 KiB) Viewed 340 times

[fechter]

Excellent, yes that should work. The 3 legged bicolor LED might be OK at 12v too, I just need to check the datasheet. Now to work on revising the layout to see if it all fits in the same size board. I can always make the board a little bigger if needed.

[teklektik]

I did a few spot checks on the 3-lead part to no avail - maybe you will have better luck. The 12v Vr oversight is looking like a fatal design flaw...

Also - I think the LED colors should be reversed to R=limit, G=HVC similar to the Voltphreaks charger; red means 'wait' - bulk charge is underway, green means bulk charging has terminated.

[fechter]

I agree on the colors.

Maximum reverse voltage on the LEDs I used in the past is 5v.

There may be another issue with the two wire LED; the output of the 358 can only pull down to about 1v at 2-3 mA. If one amp is hanging around 3V and the other one is 1v, that doesn't leave enough to light up the LED. There are some other amplifiers with rail-to-rail output that could possibly overcome this but there would still be a big difference in the current between the red and green sections.

More head scratching....

[fechter]

OK, I think this one addresses all the problems but takes quite a few parts. I'll have to see if I can squish it into the layout.

By using separate resistors for the LEDs we can also get the current matched between them a bit closer.

Mini Limiter Board schematic 3e.jpg (38.64 KiB) Viewed 299 times

[teklektik]

Cool - too bad about the parts count, but the extra features are well worth it.

[fechter]

I pretty much had to start from scratch on the layout, but I think it turned out pretty good.
I made the board just a few millimeters taller than the ver.2 boards to fit everything.

I was able to place the adjustment pot near the top so it is easier to reach.

The LED is also along the top, and the leads are oriented to make it easy to bend at 90 deg. if desired. This might be good for the clones with horizontal terminals. It would also be possible to mount the LED on the 'bottom' of the board since the board sits upside down on these supplies.

All the resistors and diodes (except the zener) are in a nice row, which makes construction faster and easier. You can stuff all the resistors and solder them all in one pass.

If you don't want HVC interface, you can leave out a diode and two resistors.

Mini Limiter V3 layout top.jpg (65.91 KiB) Viewed 290 times

Here's what the top side layout looks like (sort of):

[teklektik]

Slick!
Sign me up for 2 when you do a board run...
( Very cool that you undertook these enhancements. )

[NeilP]

Not trying to knock any of the work at all, but what does this board do different to the original single pot current limiter? I see the HVC function, but what about charge monitoring for end of charge shut down? like the three pot?

Maybe this is just a personal thing, but that function is more useful than the current limiting. Current limiting can be done on the board, much simpler with the pot/resistor mod. To my mind, if someone is going to the trouble,effort and expense of building the board it has to offer more than you can get with 20 minutes work and less than a couple of dollars worth of components ..I a pot and some wire to do resistor mod (S or NES series) ...

I see the HVC can do that , but it requires an external input..cant that be incorporated in the board??

[fechter]

I'm need to revise the 3 pot version as well. It does need some serious corrections. I'm just trying to get the mini limiter going first.

The Ver3 layout also has an extra set of holes for the shunt, so double current will be supported by adding a second shunt. If not using the second shunt (even if you are I guess), the extra holes could be used for wires going to an analog meter. With a single shunt, 10 amps will be 50 mV across the shunt. I've seen some nice analog meters with 50 mV scales on Allelectronics and some other surplus places.

[NeilP]

I'm need to revise the 3 pot version as well. It does need some serious corrections. I'm just trying to get the mini limiter going first.

Ah that is OK then, as long as it is not being side lined

[teklektik]

Maybe this is just a personal thing, but that function is more useful than the current limiting. Current limiting can be done on the board, much simpler with the pot/resistor mod. To my mind, if someone is going to the trouble,effort and expense of building the board it has to offer more than you can get with 20 minutes work and less than a couple of dollars worth of components ..I a pot and some wire to do resistor mod (S or NES series) ...

Yep - it's a personal thing Moreover, the new HVC functionality makes an equivalent boardless direct MW hack less attractive.

I see the HVC can do that , but it requires an external input..cant that be incorporated in the board??

No - a primary use of the HVC is to easily hook the MW up to CellLogs or similar that do cell-level rather than pack-level monitoring. As one example using the new v.3 board: if the pack is hooked for cell-level monitoring and low rate balance charging in parallel with MW bulk charging, then the first cell that hits CellLog HVC terminates the MW bulk charge and the pack finishes and floats on the balance chargers. Here the extra functionality of the 3-pot board is unnecessary and is accomplished by other means.

This brings us to a fundamental difference in the 1 and 3 pot solutions: the 1 pot solution with HVC is more like a building block for DIY (cell-level) charging solutions with other unspecified external elements while the 3 pot board provides more of a complete pack-level charge solution in its own right.

So - different strokes for....

[NeilP]

I think maybe I did nto explain myself very well. I see your points and understand...

the 3 pot version does HVC monitoring too, which I do use on occassion when I have apcked connected up to me tppacks HVC/LVC parallel boards. I think more what I am tryign to say is..why re design and use the single pot board, when the three pot already does it. This time spent revising the single pot board and addding extra features to it may have been better spent revising the 3 pot board rather than biinging up the spec of the single pot baord to that approcahing the 3 pot version

I suppose the advantage of the single pot board is that it is cheaper because of less components, but the difference in cost had to be marginal

[Degull]

Fetcher's V3 Mini Meanwell Limiter boards have been order and should be ready next week. This is a very limited run and the price is going to be around $10 per board. The price might be considered a little high for such a tiny board but this is because we decided to order a small quantity. It's hard to judge the demand and neither of us would like to be stuck holding a bunch of unsold boards.
I will start a new thread once we receive the boards. If anyone would like to pre-order now just send me a PM and I will start a list.

[fechter]

On to the 3 pot version...
Below is the latest revision that should solve issues with the older design. The HVC interface works differently though, as this has a different intended function. In the new design, when HVC tiggers, it will cut off the charge current and latch in the float mode. The older design lowered the current but not to zero and would not latch off.

The way the circuit is intended to work is similar to the mini limiter in the way it adjusts the current limit. In addition, when the charge current drops below a certain level set by the EOC current pot, the output voltage of the Meanwell will drop to a 'float' voltage, set by the float pot. Since this stops the charge current, the circuit will latch off until the pack voltage gets drained below the float setting. In practice, you'd set the CV setting on the Meanwell to your maximum charging voltage (say 4.2v/cell for example). On end of charge, the float setting would be 4.0-4.1v/cell and the charge current would be zero (or slightly draining) until the cells reach the float setting. The pack then needs to be discharged somewhat below the float setting before the current can go back up.

I'm not sure how useful the HVC input is. It would save some stuff if it was left out.
I'm also not sure if it needs a manual restart. Normally it should not need it if the voltages are dialed in right, but could be used to 'top off' a nearly full pack.

3 Pot Meanwell Charge Controller 4.1.jpg (45.61 KiB) Viewed 542 times

[teklektik]

I'm not sure how useful the HVC input is. It would save some stuff if it was left out.
I'm also not sure if it needs a manual restart. Normally it should not need it if the voltages are dialed in right, but could be used to 'top off' a nearly full pack.

As with the mini-limiter, the HVC input does offer some options from external cell-level monitoring - so seems valuable and can be left unpopulated if not desired.

I think the only question is the desired behavior of that external input. Just playing Devil's Advocate here - if the external input did not latch, then when the external alarm was removed, charging would resume until the internal cutoffs bought charging to conclusion normally or until the alarm re-asserted. This might cycle in and out of alarm a while until all the cells became charged enough to trip the internal cutoff. If this doesn't seem like objectionable behavior then removing the HVC latch could be good. If so:

(I'm kind of rushing this out, but I think this is correct ):
It seems the latching effect as it relates to the HVC input is tied in part to the response time of the MW in comparison to the voltage drop at the collector of Q. If a bit of damping is introduced with a small RC hung from U2b to Gnd (across R11+R8), then when HVC goes high, the voltage at the Q collector will fall more slowly presenting a declining voltage to U2 indicating a declining 'apparent' current. The apparent current will seem very high initially in the limiter zone, drop into the middle no-limiter range, and finally fall to the float cutoff level. A true pack current higher than cutoff will prematurely terminate this decline with a voltage across R8, allowing normal charging to resume. The RC constant should only need to be large enough to safely allow the MW response to outrun the voltage decline across the no-limiter voltage zone and should not materially affect normal operation.

A side effect of this modification is that a manual reset could be accomplished with a pushbutton from HVC to Gnd. (Another way to look at this is that manual reset takes an additional RC, and by the way, the HVC works a little differently....)

[fechter]

Yes, I think you got it. Previous version was intended to work with a shunt based balancer and HVC was intended to throttle the charge current.

It could be designed to either latch or not latch. I'm just not sure what most people would want.

[teklektik]

It could be designed to either latch or not latch. I'm just not sure what most people would want.

I vote for 'no latch'. However, if the above modification actually works (?), then the latching can be enabled by omitting parts - so it's two mints in one...

[fechter]

The new mini limiter boards arrived.

First thing I noticed was where I messed up and put a part label across two traces creating a short. I personally fixed every board in the batch and tested with an ohmmeter to resolve the problem. I should know better by now. In the layout file it looks like there's a tiny bit of clearance but the actual board came out shorted.

Ver.3 oops.jpg (64.38 KiB) Viewed 472 times

Other than that, they look great. I have one built and bench testing was stellar. Construction is a breeze too with the improved layout. I'll post pics when I get a chance in a new sale thread.