Maha MH-C9000 SUPPORT / FAQ Thread

[coppertrail]

I realize that not every juristiction is the same, but I find that 99% our "power outages" here locally, are less than a second or two - typically only as much time as it takes for the power company's back-up systems to switch over to another source. But long enough that it would cause the problem mentioned above. In my case, I'm just looking to have UP for the transition time so a very small UPS is more than enough. You could probably find a few other gadgets to hook into it that you wouldn't normally have backed up.

Thanks BVH, I'll be picking up one of these tonight.

 

[BVH]

Just another thought. Many UPS's tout they also provide power conditioning/surge suppression etc. Some of the higher priced, larger units probably do provide excellent protection in addition to the backed-up power. If you're buying a small UPS with little or no protection, don't forget to use a good surge protector in addition to the UPS to protect your connected equipment. Look closely at the specs to know what you're getting.

 

[EngrPaul]

Here's a thought.

Q: Why doesn't the charger remember it's settings?
A: Because the power is interrupted.

Q: What do manufacturers do to keep devices remembering their settings when the power goes off?
A: They install low-drain battery-backups.

Q: What are those little cylinders you put in a battery charger?
A: Batteries.

Q: Well, if there are batteries in the device, couldn't it use them to remember the settings?
A:

 

[RobSpook]

Well, why not just use a few simple capacitors? Cheap eh?

 

[EvilLithiumMan]

BVH brings up a good point. There are two general classifications UPS, "online" and "offline". With an online UPS, the inverter runs 100% of the time, so when input power fails, there is no unterruption of the output, the inverter was already running. But an offline UPS uses a relay or electronic switch to connect the input power to it's outlets when input power is present. When input power fails, there is a response time when the UPS logic has to determine the input has failed, the inverter must be switched on and the output connected to the inverter.

This "switchover" time is usually in the range of 10 to 40 milliseconds, usually a very safe range for computer power supplies. But I doubt there is any "headroom" in the AC power brick/wall wart that is used for our chargers.

Needless to say, the online UPS is more expensive, as the inverter is running all the time. The offline approach is what lower end UPS's usually use. And their spec. sheet should state what the dropout time is.

 

[N162E]

P.S. Don't be envious. You don't know how many sleepness nights I spent before the purchase although I got a very, very good deal!

OK Bill, I give. I am envious too. I'll be the one to ask. What did you take that thermal image with? I want one.

 

[EngrPaul]

The input is 12VDC. The device will run off a vehicle power outlet. You could consider using a 12VDC rechargeable battery in parallel to the input

 

[BVH]

EMan, what is the maximum millisecond response time people should look for in an "offline" UPS to be safe for this use?

 

[Mike abcd]

Firmware can easily handle this. They seem to have a power on start up routine from the posts I've seen. If it finds cells inserted in that check, it should flash the display and NOT attempt to charge the cells. Just sit there until the cells are removed or the user presses a button.

No additional hardware required just some better thought out firmware. To be fair, it's a common flaw with chargers. One hopes for improvements though particularly when all it takes is some common sense.

Mike

 

[wptski]

OK Bill, I give. I am envious too. I'll be the one to ask. What did you take that thermal image with? I want one.

Fred:

A Fluke Ti30.

 

[willchueh]

Mike,

This is an excellent suggestion. I'll pass it on to the development team!

Thanks again.

William

Firmware can easily handle this. They seem to have a power on start up routine from the posts I've seen. If it finds cells inserted in that check, it should flash the display and NOT attempt to charge the cells. Just sit there until the cells are removed or the user presses a button.

 

[BVH]

William, will firmware upgrades be available at some point in the future? (understanding, of course, that the unit will have to be sent back for the flash) Will future chargers, maybe even later versions of this one, have end user flash capability via USB port as others have inquired here on CPF?

 

[EvilLithiumMan]

"Better thought out firmware" is exactly right. Take the following scenario - the charger is charging a cell at a high rate, let's say 2000ma. The charger will terminate when it senses -dv/dt. Assume the cell is 10% charged and then the power goes out for 5 seconds. During that 5 second lull, the cell's voltage will drop. When power returns, the firmware is going to see a lower cell voltage. We know this isn't because of a true -dv/dt situation, but if the firmware isn't designed properly, it will terminate the charge because it sensed a -dv/dt. I wouldn't want that.

BHV - I have a line dropout generator. I am in the process of setting it up now and I will test both the MH-C9000 and BC-900 to see what they can tolerate.

 

[Mike abcd]

"Better thought out firmware" is exactly right. Take the following scenario - the charger is charging a cell at a high rate, let's say 2000ma. The charger will terminate when it senses -dv/dt. Assume the cell is 10% charged and then the power goes out for 5 seconds. During that 5 second lull, the cell's voltage will drop. When power returns, the firmware is going to see a lower cell voltage. We know this isn't because of a true -dv/dt situation, but if the firmware isn't designed properly, it will terminate the charge because it sensed a -dv/dt. I wouldn't want that.
...

I'd MUCH rather have that than ruined cells or worse because it started charging fully charged cells again...

The ideal is that it "remembers" what it was doing but that takes extra hardware and that costs money. My suggestion is simple to implement, costs nothing in hardware and is SAFE. Someone else might come up with something better but I can definitely live with having to restart charging or discharging as long as I don't have ruined cells or worse.

Mike

 

[willchueh]

EvilLithiumMan,

MH-C9000 does not have NVRAM so it is not possible to remember data while powered off.

William

"Better thought out firmware" is exactly right. Take the following scenario - the charger is charging a cell at a high rate, let's say 2000ma. The charger will terminate when it senses -dv/dt. Assume the cell is 10% charged and then the power goes out for 5 seconds. During that 5 second lull, the cell's voltage will drop. When power returns, the firmware is going to see a lower cell voltage. We know this isn't because of a true -dv/dt situation, but if the firmware isn't designed properly, it will terminate the charge because it sensed a -dv/dt. I wouldn't want that.

 

[Mike abcd]

Mike,

This is an excellent suggestion. I'll pass it on to the development team!

Thanks again.

William

Glad to see you're open to suggestions for improvements.

Please also pass the other suggestions already posted on to the development team.

- If multiple cells are inserted within 5 seconds, the charger should flash the cell indicators of those slots at the same time and only require setting the parameters once for all the cells that were inserted at the same time. If a user wants separate settings, he should be forced to insert each cell individually and set its parameters.

- When performing one or more refresh cyles, the result of the LAST discharge cycle should be available as soon as it completes. The user should NOT have to wait until the end of the one hour rest cycle to see the result. It would be even better if you can check the amount discharged at any time during the discharge cycle. Progress checks are frequently useful.

Mike

 

[moldyoldy]

just some data on power lines for your rumination. In case you don't think that you need a UPS......

A common feeder from a power station is 13800VAC 3 phase @ 4000-5000Amps in a Y configuration. If a phase fault occurs, a common high-voltage vacuum breaker will break the circuit w/in 10-15 cycles. It takes about 5 cycles for the breaker to stabilize after opening. The average breaker is set to reclose in 5 seconds or so. That constitutes the two "bang.....bang" hits that happen when a main feeder goes out. Spectacular if you should happen to be anywhere close - hopefully not! If the line is still in fault, the breaker reopens and stays open. Human intervention is then required.

Another note about feeder faults. If one phase shorts to ground, the next close of the breaker will usually find another phase shorted to ground. Suffice to say that with currents of the magnitude that will flow to ground during a short-circuit condition on a feeder line will cause signficant neutral and ground currents to flow. At that voltage, the ground is a nice high-wattage resistor. I will let you do the multiplication..... The end result is that both the neutral and the ground in the area will NOT be at zero volts. What that voltage could be is dependent on how close your sensitive equipment is to the fault or the power station. A mile or two at those voltages and currents is not much protection if the current should happen to flow on the surface of the ground!

As for the typical UPS, I happen to have the APC Backup UPS ES 750 with tel and coax protection. equivalent to 450watts. The transfer time to battery in a failure is listed as 6 milliseconds typical and 10 milliseconds maximum. In general, the company I work for has good experiences with the APC units in comm closets. Besides my own unit, I installed APC UPS units at a couple churches - no call backs at all, and yes, they are in use.
There are other good UPSs, but as was pointed out above, pay attention to the noise reduction, not just the spike/surge protection!

Tim

 

[jtr1962]

Since nobody asked I'm curious about the LEDs used in the backlighting. Are they designed to remain bright after thousands of hours of use? Typically, 5mm and other types of small LEDs will have a useful life of a few thousand hours unless underdriven. Can we assume that Maha put as much thought into the backlight as it did into the rest of the charger? I really like the charger so far. My only real concern at this point is the long term usefulness of the backlight.

 

[Curious_character]

I got my MH-C9000 today, and it's nearing the end of the discharge part of its first refresh/analyze cycle with 4 2300 mAh cells. I set the charge rate to 1 A and discharge to 500 mA. The cells are now at about 1.10 - 1.15 volts, and I see that the discharge current on one station has dropped to about 300 mA and is dropping fairly fast. Another is at about 420 mA and dropping. The lowest voltage cell is still near 500 mA.

At what part of the discharge cycle does the discharge current begin decreasing? Does the charger use the actual current in its calculation of battery capacity, or does it assume that the discharge current is what I specified?

c_c

 

[EngrPaul]

Since nobody asked I'm curious about the LEDs used in the backlighting. Are they designed to remain bright after thousands of hours of use? Typically, 5mm and other types of small LEDs will have a useful life of a few thousand hours unless underdriven. Can we assume that Maha put as much thought into the backlight as it did into the rest of the charger? I really like the charger so far. My only real concern at this point is the long term usefulness of the backlight.

LED's will dim over time. The charger display is generously sized and extremely readable, so even at 20% brightness at end-of-life it will be fine.

I'm more concerned about my fading eyesight in the next few years... as I will start needing reading glasses like all my peers... :lolsign: