BVM-8s - new 1-8 cells battery monitor device?

[cor]

There s a mod for I think the celllogs to make them draw from all cells
Alternately you could mod it to draw power only from external aux battery and tape one to the back.

The BVM is slightly different from the celllog in that it uses a standard LDO to generate 3.3V from a quick glance inside one.
I also noticed 2 diodes from the 1st and 2nd cell to this regulator.
There is a pair of diodes to power the two quad LM324 opamps but the power draw of those is seriously lower than the processor and backlight.
It will probably still work to add a switch in the negative wire (which internally is connected to the ground of the unit).

One other intriguing thing is 5 mounting holes next to the 3-pin alarm port. I wonder if that is meant for (micro-)USB? After all, the 'S' at the end of the name stands for the serial communication like with the celllog: the -S has USB, the -M has not.
Maybe the software is not implemented enough to support USB?
Anyway, this device does not have the ridiculous powering as the early celllog had, which had a fixed 2k resistor from the highest cell and burned the power away in a 431 set to 3V.

 

[cor]

Here is a suggestion how to turn a battery monitor off using an opto plus any N-channel MOSFET and 3 resistors. Wire the opto input to a keyswitch signal or monitor enable. You can put any number of monitors with this circuit in parallel or series and tie all enable inputs together, so you can turn them all on/off at the same time:

 

[Hyena]

Or you could just put a switch in the -ve balance tap wire.
I just bought a 3PDT switch to wire to my 3 units connected to my 18S pack so I can turn all 3 on with the flick of a switch

 

[cor]

Sure, I just like to stow everything away and not dig out a switch to the packs, so I prefer to be able to switch them from a key signal or some other enable switch that is already on the bike...
I noticed that there were some questions about finding a 3-pole switch, so I made a universal solution that will work with any nr of packs.

 

[cor]

I have a few days more experience with running the BVM-8S and I can certainly see them drawing from the first two cells, so much that I am guessing the draw is about 50mA, because in less than 4 days the first two cells are about halfway down (10Ah pack) so the draw may even be 60mA, I still need to measure it.
Anyway, if you leave these on a *full* 10Ah pack then you can expect trouble after a week....
Another thing that I am seeing is that the backlight is much dimmer after running continuously for about a week.
I have seen before that some cheap copies slightly over-drive LEDs and those LEDs quickly lose their brightness, but I did not expect that after 1 week the brightness would be so much down. You can still read them well in artificial light conditions, but in daylight it will be difficult to read them soon...

 

[cor]

There are quite big bugs in the BVM software.
The voltage measurement seems quite OK,
but the charge percentage is bogus. It indicates too low and does not follow the normal charge profile.
At a relatively high voltage of 3.67V the indication is only 8% charge left, which is incorrect because the cell is still almost half full.
At 3.777V the percentage suddenly jumps from 13% to 27% instead of incrementing.
From that point it ramps up way too fast, only 0.05V higher adds another 14% (though it does increment normally, not make a step) !?!
Around 3.91V at 61% the increase seems to slow down: 3.97V is 71% - 4.000V is 75% and this continues: 4.010V is 77%
4.014V is 78% = 4.020 is 79% - 4.028 is 80% - 4.040 is 81%
No matter how high I charge (between 4.2 and 4.3V) it never goes beyond 81%
So there is certainly something broken in the software.
I also hate not to be able to set a high voltage threshold - they are now only good for discharge monitoring and *manual* charging...

 

[dumbass]

I have been using the CellLog8s for about 2 years and never had a complaint (except for the manual). In my opinion the BVM-8 is a crappy look-a-like. I bought 4 of them and this morning I replaced one of my CellLogs with a BVM-8. To start with the settings are not as fine as with the CellLog. Secondly, the alarm that is supposed to be 90db is a joke. Yes it is much loader then the internal alarm on ether the CellLog or the BVM but it's not close to be 90db. I have been using a 90db external alarm from Radio Shack for 2 years and you can hear that thing on the next block. But the BVMs 90db alarm I would not hear while riding in trafic or with a good wind blowing.

On the CellLog you can program the external alarm for no or nc. You can not do this on the BVM. In my opinion SAVE YOUR MONEY and go with the CellLog8s and leave the BVM-8s for the RC guys. I'll be ordering a 4 more CellLog8s tomorrow for my new packs.

Bob

 

[cor]

Anybody having a Battery Monitor that is broken or unused? I have interest on short notice, so let me know!

 

[dumbass]

Anybody having a Battery Monitor that is broken or unused? I have interest on short notice, so let me know!

Not sure exactly what your asking. Are you looking to buy some unused BVM8s or CellLog8s ?

Bob

 

[cor]

Hi Bob, Yep, either one.

 

[dumbass]

Hi Bob, Yep, either one.

OK, I have 3 brand new BVM8s in the box never opened that I will sell. I already have CellLog8s on all my other projects but when I wanted to buy more they were out of stock so I bought the BVM8s in stead but also ordered the CellLogs as well. So now I have 4 BVM8s and 4 CellLog8s. I'm going to keep the CellLogs because I know better how to set them up. But the BVM8s are available for sale. PM me if your interested.

Bob

 

[MAGICPIE3FOCUSPOWER]

I have two new BVM 8S hmmmm backlight is now very dim.
So don't waste your money and buy a Cell Log 8M (didn't know this one exist).
I don't want the version with USB (don't use it).

 

[TheBeastie]

I have two new BVM 8S hmmmm backlight is now very dim.
So don't waste your money and buy a Cell Log 8M (didn't know this one exist).
I don't want the version with USB (don't use it).

I have 2 Cell-Logs from HK and one is totally dodgey, screen is all dim and it ramdomly just pixelates all up until I unplug it and replug it in.
I got 1 BVM and its far easier to read and solid screen performance.
Just saying it can go either way....

 

[MAGICPIE3FOCUSPOWER]

Hmm good to know!
Thanks for sharing your info!

I have almost bought the Cell Log 8M

But I have performed the backlight mod for BVM-8S (founded at Youtube).
Just add 100 ohm resistor in serie with the OEM resistor.
Hopefully led backlight will now last longer

 

[3nslav3]

for the people that are intrested:

Ive made some high res pics of the inside of the BVM-8S (this is a rebranded BVM-8S called Fusion Smart Alarm but it's basicly the same thing)

back:

Back resistors close up:

Behind the screen:

Diodes close up:

screen:

I've been using these things for a months now (perm mounted in my battbox) with a switch on the negative lead without problems :wink:

http://youtu.be/AXGAj-Z2CXs

[youtube]AXGAj-Z2CXs[/youtube]

 

[MAGICPIE3FOCUSPOWER]

Thanks for your pictures

I have opened mine....... well one of them is very low quality...
Backlight positive wire were soldered to the alarm leg

So more current to backlight >>> burning out...

 

[jumpjack]

Doesit exist a logging version of this device? Adding an sdcard to an atmel/arduino is a matter of few euros! Who neds usb connection if you can remove the memory card?

 

[zeccato]

but it does not give you an option to set a high voltage alarm..,......

Do you know how much is set for lifepo4 cell the
high voltage alarm?
until today does not give you an option to set a high voltage alarm?

 

[eMark]

What previous scenario have you experienced where you wished you would have at least had a "dumb smart" BMS with a high voltage alarm? By "dumb Smart" referring to a non-bluetooth BMS with preset voltage alarm (200mV disparity).

What you may be referring to is an alarm when the voltages between any of the cells or P-groups differs by more than say 200mV (see 5th post on page 1). Is that really a high voltage alarm if the cell or P-group never exceeds 4.2V, but there is a 200mV difference between two cells or two P-groups. Ideally the individual cells or P-groups should be within at least 30mV.

Would be nice if it could be set at only 50mV or 100mV difference depending on the age of the pack (e.g. 4.10V and 4.15V or 4.10V and 4.20V). Don't you need a programmable bluetooth BMS with a good app for programming to your specification? If there is a difference of 200mV then never charge to even 4.1V (which is normally a good idea) as one cell or P-group could be at 4.1V, while another cell or P-group could charge to 4.3V before the alarm goes off ... so whether 200mV low voltage alarm (e.g. 4.1V and 3.9V) or 200mV high voltage alarm (e.g 4.1V and 4.3V) it's in the eye of the DIYer's inexpensive cell logger alarm.

 

[zeccato]

What previous scenario have you experienced where you wished you would have at least had a "dumb smart" BMS with a high voltage alarm? By "dumb Smart" referring to a non-bluetooth BMS with preset voltage alarm (200mV disparity).

What you may be referring to is an alarm when the voltages between any of the cells or P-groups differs by more than say 200mV (see 5th post on page 1). Is that really a high voltage alarm if the cell or P-group never exceeds 4.2V, but there is a 200mV difference between two cells or two P-groups. Ideally the individual cells or P-groups should be within at least 30mV.

Would be nice if it could be set at only 50mV or 100mV difference depending on the age of the pack (e.g. 4.10V and 4.15V or 4.10V and 4.20V). Don't you need a programmable bluetooth BMS with a good app for programming to your specification? If there is a difference of 200mV then never charge to even 4.1V (which is normally a good idea) as one cell or P-group could be at 4.1V, while another cell or P-group could charge to 4.3V before the alarm goes off ... so whether 200mV low voltage alarm (e.g. 4.1V and 3.9V) or 200mV high voltage alarm (e.g 4.1V and 4.3V) it's in the eye of the DIYer's inexpensive cell logger alarm.

On my lifep4 i have buzzers when I go far.
(but in the future I buy li-ion).
I'm interested in HV alarm with warning beeper to charge without bms the battery at 90-97%, with c.c c.v adjustable 0-60V 0-11A Gophert.

To balance I have a balance charger, and I also need it to build my future battery.

I was thinking smart bms,
but I want to have as few things as possible, and simpler (non-complications), and I don't trust bms very much.
And I've seen that without bms the bike works better.

I was just looking for a simple non-BT monitor HV alarm with warning beeper like the cellog.

 

[john61ct]

Do you know how much is set for lifepo4 cell the high voltage alarm?

You keep resurrecting zombie threads!

Few members around in 2014 are likely to still hang out here.

And the data in threads that old is best left archived, tech marches on.

Some LFP makers spec 3.6V or even higher as a "stress maximum" but 100% SoC can be reached at 3.45V, depending either on C-rate if CV only, or endAmps or Absorb Hold Time setpoints

all of which vary depending on the charger.

 

[zeccato]

Do you know how much is set for lifepo4 cell the high voltage alarm?

You keep resurrecting zombie threads!

Few members around in 2014 are likely to still hang out here.

And the data in threads that old is best left archived, tech marches on.

Some LFP makers spec 3.6V or even higher as a "stress maximum" but 100% SoC can be reached at 3.45V, depending either on C-rate if CV only, or endAmps or Absorb Hold Time setpoints

all of which vary depending on the charger.

Yeah :lol:
but still, I heard he has no HV alarm,
That's all I was asking, about the audio alarm, not what you guessed, thanks anyway.