bluetooth BMS?

Batteries, Chargers, and Battery Management Systems.
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Re: bluetooth BMS?

Post by ElectricGod » Feb 21 2018 1:17pm

Fionn wrote:
Feb 21 2018 7:56am
ElectricGod wrote:
Feb 20 2018 2:17pm
see those 2 solder holes at the middle, right hand edge of the board? That's P-. Connect your EV here. If you care about having mosfets that control charge then run your charging port to C-. I'm never concerned with charge current. AT it's best, it's maybe 50% of discharge current so I never use C-. Charging and discharging for me always go through P-. Also, if you use regen, that happens through P-...that's just a form of charging. If that's safe through P- and it is, so is regular charging through P-. For the super safety conscious types, C- might have a place in an EV, but more most people it's completely extraneous. Never power your EV through C-. It can be done, but you double the mosfets in series and the related losses. What's the point in doing that? Why they show powering the EV from C- is a mystery to me. I sure wouldn't do that! I'd prefer to have all those wasted C- mosfets on the P- side where they actually matter.

Of course I've connected up BMS wrong before too. This is a couple of 16S 50 amp BMS that are currently in use and connected via the C- port, not P- (center solder hole)...DOPE! It works, just not optimal.
I'm interested in using the charge termination to limit charging to lower than the standard charger output (or above what it's set to as an additional safety net).
I also have an interest (like one or two other posters here) in using these with lithium based renewable energy systems where having separate load and charge disconnects is very useful.
I hope to try and trace out a partial schematic for this board over the weekend to make sense of the implementation.

As you say, they seem to be recommending running power through both FET banks, which is not an optimal solution.
Also, it seems strange that both FET banks drains are connected together while the load current is expected to pass through them in series.
Does this not mean the charge FETs are reverse biased?
N channel fets.jpg
Mosfets don't have diode junctions for drain to source inside the mosfet. I'm not referring to the back diodes either. The mosfet itself is not forward or reverse biased drain to source or source to drain. Current flows either direction through the mosfet. This is why connecting to C- for power works. You are correct, from a bipolar transistor perspective, "flowing backwards" . Bipolars do have a diode junction from collector to emitter that allows current flow in only one direction. From the perspective of convention and general logic, there is a forward direction and a backwards direction for mosfets, but in reality, no not really. I'm referring to pure mosfets with no back diodes. Add the diode and then you have design limits that may effect how you use the mosfet. Also, even the craptastic HY3410 probably has a lower Rds than the back diode so if the charge mosfets are on, they are going to be doing the lion share of conducting current despite the fact that the back diodes are forward biased in the C- mosfets in a BMS.

This reminds me of another detail. If the C- mosfets turn off, the back diodes do NOT turn off and they continue to conduct since from C- to the internals of the BMS, they are still forward biased. IE: Getting the BMS to actually stop charging in an over current situation wont happen. It will just be limited somewhat by the higher resistance of the back diodes. I'm going to guess that the diode compared to the 100mOhms of the mosfet is 50% more resistance? I really don't know for sure since I've never tested this and haven't looked at the data sheet to see if this is a listed spec or not.

For your set up, you want to connect your charger to C- and the EV to P-. It can all be run from P- or C- and still work...just less optimally from C-. Of course, charging from C- also requires flowing current through 2 sets of mosfets in series. IMHO, this too is less than optimal.

These BMS look to support charge current limiting via the PC app only, but I haven't messed with it at all since I deliberately avoid the C- mosfets. My suspicion is that the charge mosfets simply shut off if the charge current exceeds the set limit. This is typically how current limiting on a BMS works. They don't regulate anything. They don't provide any form of constant current control. Consider them to be an on/off switch and nothing more. If you want to limit charge current, do that at the charger. All of my chargers have a bank of resistors on them for this purpose. My method is rather "brute force" in nature, but very simple to use and implement. The best way to limit current is to drop the output voltage of the charger to closer to the current pack voltage. There are after market boards that can integrate with most PSU's for this purpose. I forget the details, but there's a thread on ES for a board that does this. If you buy a well designed charger, they usually have this function built into them in some way. That is the way to limit current when charging. The BMS charge mosfets are just on/off switches. I seriously doubt they do more than that.

For anything 100 volts or less and you want a robust and well designed, highly flexable charger, consider buying the Chargery C10325 charger. It does real CC control, voltage control and lots more and it's good for 1500 watts. Good luck trying to blow it up. It's fully protected. Of all the manufactured chargers I've tried out, it's my favorite.
http://www.chargery.com/C10325.asp
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Re: bluetooth BMS?

Post by ElectricGod » Feb 21 2018 1:41pm

Fionn wrote:
Feb 21 2018 12:07pm
ElectricGod wrote:
Feb 21 2018 11:52am
you don't really think you will get customer service from a Chinese seller do you? They work 100% on bare minimum margins. Warranty replacement for this component is unlikely IMHO.
I've gotten the best customer service I've ever received from AliExpress sellers where I lodged claims on, or shortly after receipt of the goods.
Only last week I received a board with some defects due to shipping damage (and poor packaging), a pot was snapped off and an electrolytic was badly dented. After sending some photos I received a full refund for the price of the item and shipping and wasn't under any obligation to return the goods.
My previous order was for 5 items, one of which was defective. The seller immediately shipped 2 replacements at no cost.

The way their marketplace works I believe is that the seller doesn't get paid by AliExpress until the customer confirms satisfactory receipt of the goods.
Hey...that's awesome! Thanks for posting that. I have purchased only a couple of items via aliexpress and had no issues so I didn't need any customer service. You've changed my perspective on buying from aliexpress.

However, having used other sources for buying from China, the customer service usually sucks and they won't support anything after it's sold. I was involved with purchasing 2000 android tablets a few years back...yes 2000 tablets...that wasn't a typo. We got them direct from the manufacturer. You'd think an order that large would create some amount of good graces and accommodation when things didn't work. NOPE! NO nada nothing. We had to over buy tablets to ensure sufficient numbers that did work correctly. The defective ones were pure loss. I think we "ate" something like 60 tablets. THat's not my only total lack of customer service out of China experience, but it's a good one.
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Re: bluetooth BMS?

Post by izeman » Feb 21 2018 2:17pm

i did another measurement for my 15s BMS with a voltcraft oszi dmm which is dedicated capable of measuring uA.

these are the results:

13mA (confirmed from my earlier measurement) when active
220uA while inactive (which confirms the sellers statement as posted in page #1 here)

these measurement will vary with different cell numbers. for a 30 cell type bms they should be around half of it.

active.png
active.png (169.16 KiB) Viewed 1392 times

standby.png
standby.png (171.61 KiB) Viewed 1392 times
now for the calculation. voltage is around 51V.
after 3 days the voltage drop on my half pack (15Ah) was around 10mV. P = U * I = 51V* 0,0002 (200uA) = 10mW

0,0002A * 72h = 0,0144Wh. or 14mWh.

with a voltage drop of around 10mV after 3 days (which is not correct, as i once connected the battery and hit the throttle which for sure made the voltage drop some mV) it would take around a year from fully charged to fully discharged.

but this does ABSOLUTELY NOT correlate with the measured 0,2mA during standby. i does check BT connecting every now and then, but there's a big gap between one year (see calc above) and the calculated 60.000h (30.000mAH / 0,2mA = 17 years)
13mA would be 30.000mAh / 13mA = 100 days. so i would mean that the BMS is 70% in standby mode and 30% active.


do you see an error in my calcs?

EDIT: seems there was something wrong with my measurement. when i switched the RANGE on the DMM from auto to FIXED, it shows around 650uA. this definetely makes more sense to me.
30.000mAh / 0.65mA = 5 years. which still is far from reality.

someone help me out! i drives me mad.
Last edited by izeman on Feb 21 2018 2:53pm, edited 2 times in total.

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Re: bluetooth BMS?

Post by izeman » Feb 21 2018 2:19pm

ElectricGod wrote:
Feb 21 2018 1:41pm
Hey...that's awesome! Thanks for posting that. I have purchased only a couple of items via aliexpress and had no issues so I didn't need any customer service. You've changed my perspective on buying from aliexpress.
aliexpress is really commited to their customers, as they KNOW that there is a lot of scam going on. i had 550+ orders from aliexpress now, and didn't have a SINGLE LOSS. i had issues (<10 orders) and ALL of them got solved to my satisfaction.

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Re: bluetooth BMS?

Post by Fionn » Feb 21 2018 2:53pm

Thanks ElectricGod, total brain fart there on my behalf from too many late nights, of course VGS is all that matter for conduction.
Yes, AliExpress truly is the exception to all Chinese retain experiences. In my opinion, apart from shipping delays it exceeds the eBay or Amazon experience.
The products often fall short of what we would expect in the West in terms of quality control but the price is commensurate and any serious issues are swiftly resolved as mentioned and backed up by izeman.

I'm not interested in current limitation on the charge control, just termination at a set voltage.
I appreciate your comments on the back diodes and will attempt to measure the leakage current with the charge FETs off.
I suspect it won't be an issue fur my purposes.

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Re: bluetooth BMS?

Post by shorza » Feb 21 2018 3:20pm

Coltheplumber wrote:
Feb 21 2018 7:26am
Regarding the Bluetooth-
On initial powering up of my BMS, the Bluetooth module had a solid blue light, neither my phone or tablet would pick up the device.
After much messing around the solution was to unplug the balance cable, disconnect the Bluetooth module, reconnect the balance cable and THEN reconnect the Bluetooth module.
Open up your app and it will now let you connect
Once paired the solid blue light will come on 😁
Thanks, I will try that. Although I don't think my module has any LEDs.
ElectricGod wrote:
Feb 21 2018 11:52am

you don't really think you will get customer service from a Chinese seller do you? They work 100% on bare minimum margins. Warranty replacement for this component is unlikely IMHO.

I suspect that you will get on ebay and find that BT board yourself in 1/10th the time it takes to get a replacement after much arguing with the seller.
It's worth a shot. They may be able to trouble shoot the problem also.

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Re: bluetooth BMS?

Post by ElectricGod » Feb 21 2018 6:36pm

shorza wrote:
Feb 21 2018 3:20pm
Coltheplumber wrote:
Feb 21 2018 7:26am
Regarding the Bluetooth-
On initial powering up of my BMS, the Bluetooth module had a solid blue light, neither my phone or tablet would pick up the device.
After much messing around the solution was to unplug the balance cable, disconnect the Bluetooth module, reconnect the balance cable and THEN reconnect the Bluetooth module.
Open up your app and it will now let you connect
Once paired the solid blue light will come on 😁
Thanks, I will try that. Although I don't think my module has any LEDs.
ElectricGod wrote:
Feb 21 2018 11:52am

you don't really think you will get customer service from a Chinese seller do you? They work 100% on bare minimum margins. Warranty replacement for this component is unlikely IMHO.

I suspect that you will get on ebay and find that BT board yourself in 1/10th the time it takes to get a replacement after much arguing with the seller.
It's worth a shot. They may be able to trouble shoot the problem also.
Ignore what I said about CS from aliexpress. Others are saying it's pretty good.
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Re: bluetooth BMS?

Post by ElectricGod » Feb 21 2018 7:31pm

Fionn wrote:
Feb 21 2018 2:53pm
Thanks ElectricGod, total brain fart there on my behalf from too many late nights, of course VGS is all that matter for conduction.
Yes, AliExpress truly is the exception to all Chinese retain experiences. In my opinion, apart from shipping delays it exceeds the eBay or Amazon experience.
The products often fall short of what we would expect in the West in terms of quality control but the price is commensurate and any serious issues are swiftly resolved as mentioned and backed up by izeman.

I'm not interested in current limitation on the charge control, just termination at a set voltage.
I appreciate your comments on the back diodes and will attempt to measure the leakage current with the charge FETs off.
I suspect it won't be an issue fur my purposes.
I'm going to sound like a scratched record...
Do voltage limiting at the charger. I build my own chargers, but that's irrelevant. I have yet to see a commercially available charger that can't be adjusted. Inside will be a small adjustment POT. Set this to your desired pack voltage. 16S LION at 4.1 volts per cell that's 65.6 volts. Adjust the charger to 65.6 volts. 20S LION...82 volts. 20S LIPO...4.2 volts each or 84 volts. That's your voltage limiter. I literally use nothing else. The BMS does balancing and discharge protection for me. The rest is superfluous.

There's something that I should mention...KISS...I don't mean to be condescending and I apologize if that's how this comes across, but seriously... Keep It Simple. There's no need for the added complexity. I don't even use breakers or fuses. If there is a major electrical issue, I turn off the contactor. Otherwise, the BMS over load protection is going to save my bacon. That's effectively a mechanical/manual fuse and an automatic fuse. Why do I need yet another fuse or breaker? My first EV was sooo safe...LOL...I had a fuse block in it so everything was individually protected. What a waste! The Chinese wiring was horrible and despite the fuses had shorted out 2 or 3 times anyway. I finally ripped out all the original wiring and did it right. At the same time I eliminated all the fuses and saved myself lots of complication. Simplifying the EV wiring gained loads of reliability in the process. Now none of my builds have fuses or breakers...just the BMS and contactor.

Voltage limiting at the BMS should be set higher than the pack voltage. I'm assuming you are using regen. If not ignore this...not relevant. Regen commonly creates very short lived surges 5-10 volts over the pack voltage. The large caps in the motor controller and the battery pack levels this out to just barely above the pack voltage. If the BMS is set to cut off at exactly max pack voltage then you get less regen recovery and less filtering of those surges.
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Re: bluetooth BMS?

Post by ElectricGod » Feb 21 2018 7:50pm

shorza wrote:
Feb 21 2018 3:20pm
Coltheplumber wrote:
Feb 21 2018 7:26am
Regarding the Bluetooth-
On initial powering up of my BMS, the Bluetooth module had a solid blue light, neither my phone or tablet would pick up the device.
After much messing around the solution was to unplug the balance cable, disconnect the Bluetooth module, reconnect the balance cable and THEN reconnect the Bluetooth module.
Open up your app and it will now let you connect
Once paired the solid blue light will come on 😁
Thanks, I will try that. Although I don't think my module has any LEDs.
ElectricGod wrote:
Feb 21 2018 11:52am

you don't really think you will get customer service from a Chinese seller do you? They work 100% on bare minimum margins. Warranty replacement for this component is unlikely IMHO.

I suspect that you will get on ebay and find that BT board yourself in 1/10th the time it takes to get a replacement after much arguing with the seller.
It's worth a shot. They may be able to trouble shoot the problem also.
I was thinking about your BT connectivity situation...
1. In android settings is a place to check for available BT connections. In there the BMS should be listed as "xiaoxiang BMS" or something like that. You can't connect to is from here, just see that it is advertising it's existence.
2. Start up the app. On my phone the app tries to connect to whatever it last knew and if it cant then presents me with a screen that lists any available BT devices. Select the BMS. Hit refresh if it's not listed.
3. In the 3 bar menu touch the icon at the top of the list to get the connection wizard.

Did that get you going? Of course you may have a DOA BT module too.
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Re: bluetooth BMS?

Post by shorza » Feb 22 2018 12:24am

ElectricGod wrote:
Feb 21 2018 7:50pm

I was thinking about your BT connectivity situation...
1. In android settings is a place to check for available BT connections. In there the BMS should be listed as "xiaoxiang BMS" or something like that. You can't connect to is from here, just see that it is advertising it's existence.
2. Start up the app. On my phone the app tries to connect to whatever it last knew and if it cant then presents me with a screen that lists any available BT devices. Select the BMS. Hit refresh if it's not listed.
3. In the 3 bar menu touch the icon at the top of the list to get the connection wizard.

Did that get you going? Of course you may have a DOA BT module too.
Thanks for the advice.
I have tried it both ways. The bms' BT name is 'minew' for whatever reason.

If I attempt to connect through the phone settings it just hangs then fails.
If I attempt to connect through just the app I get a notification similar to 'unable to connect'.

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Re: bluetooth BMS?

Post by ElectricGod » Feb 22 2018 1:30am

shorza wrote:
Feb 22 2018 12:24am
ElectricGod wrote:
Feb 21 2018 7:50pm

I was thinking about your BT connectivity situation...
1. In android settings is a place to check for available BT connections. In there the BMS should be listed as "xiaoxiang BMS" or something like that. You can't connect to is from here, just see that it is advertising it's existence.
2. Start up the app. On my phone the app tries to connect to whatever it last knew and if it cant then presents me with a screen that lists any available BT devices. Select the BMS. Hit refresh if it's not listed.
3. In the 3 bar menu touch the icon at the top of the list to get the connection wizard.

Did that get you going? Of course you may have a DOA BT module too.
Thanks for the advice.
I have tried it both ways. The bms' BT name is 'minew' for whatever reason.

If I attempt to connect through the phone settings it just hangs then fails.
If I attempt to connect through just the app I get a notification similar to 'unable to connect'.
The only way you can connect is via the app. Oh well...I guess it's defective.
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Re: bluetooth BMS?

Post by Coltheplumber » Feb 22 2018 6:13am

shorza wrote:
Feb 22 2018 12:24am
ElectricGod wrote:
Feb 21 2018 7:50pm

I was thinking about your BT connectivity situation...
1. In android settings is a place to check for available BT connections. In there the BMS should be listed as "xiaoxiang BMS" or something like that. You can't connect to is from here, just see that it is advertising it's existence.
2. Start up the app. On my phone the app tries to connect to whatever it last knew and if it cant then presents me with a screen that lists any available BT devices. Select the BMS. Hit refresh if it's not listed.
3. In the 3 bar menu touch the icon at the top of the list to get the connection wizard.

Did that get you going? Of course you may have a DOA BT module too.
Thanks for the advice.
I have tried it both ways. The bms' BT name is 'minew' for whatever reason.

If I attempt to connect through the phone settings it just hangs then fails.
If I attempt to connect through just the app I get a notification similar to 'unable to connect'.
"Minew"! Sounds like your hitting on a different device, my app lists a few local Bluetooth devices when I start it up.

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Re: bluetooth BMS?

Post by Fionn » Feb 22 2018 6:45am

Coltheplumber wrote:
Feb 22 2018 6:13am
"Minew"! Sounds like your hitting on a different device, my app lists a few local Bluetooth devices when I start it up.
Same here, mine picks up a distant TV set even.

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Re: bluetooth BMS?

Post by shorza » Feb 22 2018 7:05am

Coltheplumber wrote:
Feb 22 2018 6:13am
"Minew"! Sounds like your hitting on a different device, my app lists a few local Bluetooth devices when I start it up.
It's definitely the BMS. It disappears when I disconnect the power. Thanks for the suggestions, . I'll keep you updated when the seller finally gets back to me. I hate Chinese New Year.

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Re: bluetooth BMS?

Post by parabellum » Feb 22 2018 11:46am

Just few personal observations about BT modules in general.
1)Some just do not pair to specific devices. Have not found solution for that.
2)Some pair but do not connect to specific devices. Have not found solution for that.
3)Some will not reconnect twice on specific devices. Must forget the BT module and pair to it new every time.
4)Some will have trouble to pair to second device, they just loop trying to connect to previous paired device. Must reset in some way and get it in pair modus if possible.
5)Some will connect but fail at every data transfer.
6)Some are just broken. :D

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Re: bluetooth BMS?

Post by ElectricGod » Feb 22 2018 12:05pm

parabellum wrote:
Feb 22 2018 11:46am
Just few personal observations about BT modules in general.
1)Some just do not pair to specific devices. Have not found solution for that.
2)Some pair but do not connect to specific devices. Have not found solution for that.
3)Some will not reconnect twice on specific devices. Must forget the BT module and pair to it new every time.
4)Some will have trouble to pair to second device, they just loop trying to connect to previous paired device. Must reset in some way and get it in pair modus if possible.
5)Some will connect but fail at every data transfer.
6)Some are just broken. :D
Exactly...I've seen every one of these scenarios.

My expensive receiver in my house has BT connectivity. Every time I want to use my phone with it to play music, I have to "forget" it and reconnect. However the $30 portable BT speakers I bought at Target can sit for months and they will connect immediately. Same for my Bose QC35's...go figure! BT, despite being rather old technology isn't exactly fool proof.
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Re: bluetooth BMS?

Post by ElectricGod » Feb 23 2018 1:01am

New shunts arrived tonight so I soldered them down on my 20S BMS.

It has upgraded mosfets...IRF4110's in place of the craptastic HY3410. The HY3410 according to it's spec sheet is good for 17 amps at 10 volts, so lets call that 2 amps at 82 volts and be super nice and liberal. AND they are Chinese HY3410's so it's a total guess how good they really are. They are also 105 mOhm each so that's 7 in parallel or 15 mOhms. 1 IRF4110 is rated for 130 amps at 10 volts and mine are legit 4110's, not Chinese ones. They also have a max Rds of 4.5 mOhms. A single IRF4110 has half the resistance of 7 HY3410's and more current handling ability than 7 HY3410's. I have 7 IRF4110's on the BMS in parallel or at worst .64 mOhms for all 7 in parallel AND conservatively at 82 volts...100 amps. Finally the HY3410 can handle 80 watts of heat while the IRF4110 can handle 370 watts of heat. So not only can each IRF4110 mosfet handle 10X more amps than all the HY3410's, but it's internal resistance is 23.3X LESS than the HY3410 AND it can handle 4.6X more heat. This BMS is going to be MUCH stronger now and probably run much cooler while doubling or more the continuous current handling ability.

I had to double up the shunts to be able to use the current carrying ability I have now in the much better mosfets. Originally 10 5 mOhm shunts in parallel comes to .5 mOhms and now there are 20 in parallel for .25 mOhms. The result will be that the current sensing will be 1/2 of reality. IF you do this mod, keep that in mind and set the current limiting to 1/2 of what you really want. OR...these shunts are 1 watt each, get 2 watt 5 mOhm shunts instead. Either one works and the BMS will work either way. I got more 1 watt shunts because I originally was going to stack them on top of each other, but when I saw they fit between the existing ones decided against it. I probably should have gotten 2 watt shunts instead so that current readings were unchanged. OH well. No harm done.

Before...

Image

After...

Image

Since I have 4 thermistors, I put 2 inside heat shrink and then bonded them to the two power busses with thermal glue. The copper buss between the mosfets is attached to the main tab on each mosfet. This will read mosfet temperatures. The other buss connects to all the shunts so that thermistor will read their temperature. Copper is a great heat conductor so within seconds whatever heat is in one place will also be everywhere else too. I'll get pretty decent readings bonded to the copper.

Image
Last edited by ElectricGod on Feb 23 2018 1:55am, edited 1 time in total.
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Re: bluetooth BMS?

Post by ElectricGod » Feb 23 2018 1:19am

IF anyone does this BMS mod, please pull off the original copper reinforcing on the busses, They are sooooooo NOT soldered down to anything! Also, the solder pads under the discharge mosfets were not bonded to the mosfets very well. I imagine the charge mosfets are similarly bonded. I did have 2 that I could see light underneath them! IF that's good bonding then I must really be an idiot. As a result there was a very poor current and heat path away from the mosfets. When I put down new mosfets, I made sure the solder pads were properly tinned and clean so that they would flow well to the mosfets. Then I tinned the backs of each mosfet. This guaranteed that good solid solder flow and bonding would happen. The copper reinforcing strips were similarly poorly bonded down and placed incorrectly. There was bonding in places, but mostly not at all. They need to make physical contact AND overlap with and be soldered down to the wire bonding pads or else they are useless. Neither of my copper strips were even close to the wire bonding pads which is completely useless. Why bother adding copper if it can't extend the current path all the way? I pulled them up, cleaned off all the oxidation and tinned them on every surface. I also did the same to the solder pad that it was supposed to bond to and was also equally incapable of holding a solder connection. I've told the seller all of this, but probably becasue of CNY, have not heard back from them. Anyway, once the copper strips were properly tinned, they were soldered down while over lapping the wire bonding pads on the BMS. I then added another short section of copper at the far end to extend copper to the end of the large buss solder pads. I also made sure that solid solder flow occurred all the way down the length of the copper reinforcements and that the tabs on the mosfets all had solder to the copper. Same for the shunts.


I have to say that the BMS is a great idea with lots of very nice features thanks to TI and some clever programmers. BUT the power handling portion of these BMS is downright pathetically implemented! Can you use them as is? Sure you can, but if you want a strong BMS then please don't leave them in this lack luster state.

I'll be buying 2 more of them soon. When I start pulling up mosfets and copper, I'll take pictures to show you the atrocious solder work. I was really disappointed!
Last edited by ElectricGod on Feb 23 2018 1:50am, edited 2 times in total.
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Re: bluetooth BMS?

Post by ElectricGod » Feb 23 2018 1:42am

Original copper buss placement...UGG!

Notice how the copper doesn't even make it to the end of the buss to the P- wire bonding pad. There is almost .5" of gap here and no copper over lapping the the actual solder pad! Notice how there is zero solder flow around the copper. It looks like it's sitting on top of the solder, not in it. That's becasue the end of this piece of copper has a 1/8" dot of solder bonding underneath it. They might as well NOT bothered to add the copper at all.

Image

This is the B- wire bonding pad. The copper isn't touching it and there is no solder flow from the copper to the bonding pad at all. Nearly completely useless. The shunts don't solder to the copper either. There was some spotty points of solder connections between the buss and the copper. The copper is at best sitting on top of the solder, but NOT in it.

Image
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Re: bluetooth BMS?

Post by ElectricGod » Feb 23 2018 1:56am

There's reasons why these BMS are so cheap...

Go read my last 3 posts! The devil is in the details.

Now that I have fixed their faults, I think this will be a decent BMS.
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Re: bluetooth BMS?

Post by izeman » Feb 23 2018 4:14am

Nice mod but imho absolutely not needed.
The modded BMS should work up to hundreds of amps based on the FETs capabilities alone. But are you going to do that?
What's the reason behind your work? Just the fun is tinkering? I understand that as I tend to do the same.
But it is needed?

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Re: bluetooth BMS?

Post by ElectricGod » Feb 23 2018 10:27am

izeman wrote:
Feb 23 2018 4:14am
Nice mod but imho absolutely not needed.
The modded BMS should work up to hundreds of amps based on the FETs capabilities alone. But are you going to do that?
What's the reason behind your work? Just the fun is tinkering? I understand that as I tend to do the same.
But it is needed?
You are right...and I did say that it could be used as is. I'm guessing you didn't read what I wrote, but rather skimmed over it. I do that too and miss stuff.

Quoting myself...
"I have to say that the BMS is a great idea with lots of very nice features thanks to TI and some clever programmers. BUT the power handling portion of these BMS is downright pathetically implemented! Can you use them as is? Sure you can, but if you want a strong BMS then please don't leave them in this lack luster state."

"Absolutely not necessary"...hmmm I definitely wouldn't go that far. They will work as is, but I seriously doubt that you can run them at 50 amps at 82 volts for very long. I would very easily do that. For people building 300-2000 watt EV's, yes defenately true, there will be no need to do anything to the BMS. For people who want a fast and strong EV (me), "as is from the factory" will not be sufficient. Admittedly, I am applying my bias, expectations and application needs to this BMS. From that perspective, they need upgrades.

And yes...I will be using it at much more than 50 amps. One BMS at 16S will see 65 amps continuous and the 20S probably 80-100 amps continuous.
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Re: bluetooth BMS?

Post by izeman » Feb 23 2018 11:01am

well i read your posts. maybe i was exaggerating. i meant: use them as they are for what the are said that they can handle.
i don't know why they seem to use different FETs and it seem your BMS has different types then mine.

you said
They are also 105 mOhm each so that's 7 in parallel or 15 mOhms
which according to the datasheet is wrong.

Screenshot from 2018-02-23 16-57-01.png
Screenshot from 2018-02-23 16-57-01.png (21.5 KiB) Viewed 1251 times

so it's 6.2mOhm compared to around 4.5mOhm. if those HY3410 were genuine. did you test them and measured internal resistance? if the real RDSon would really be so ways off i will rip mine off the board instantly.

beefing up the traces and making the FETs have good contact (without air gap in between) is always a good idea and never hurts though.

BTW: did you ever measure the standby current of the BMS? i'd be interested to see if only my BMS sucks the battery dry so quickly.

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Re: bluetooth BMS?

Post by izeman » Feb 23 2018 1:03pm

update: lost 27mV per cell after 5 days of standby. (15s, 15Ah battery)
interesting: first day 2mV / day, third day 4mV / day, fifth day 5.4mV / day. if this continues it will be empty quite fast - well, still around a year for a fully charged 30Ah pack, but still ...

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Re: bluetooth BMS?

Post by Fionn » Feb 23 2018 2:13pm

Without a doubt the assembly is poor, the components used are questionable, the documentation is non existent and both the PC and phone apps have plenty of room for improvement.
That being said, the TI chip at their core is very capable and with a bit of input from everyone on here they have potential to be very usable as you say.
I'm not aware of any other low cost board that had the TI BQs pre integrated with the balancing circuits, interface etc.
My own approach is to buy the low current models and replace the FETs with high quality ones and check over everything else. The cost of the board is only 7 times what the TI chip alone costs in retail quantities.
Last edited by Fionn on Feb 23 2018 2:36pm, edited 1 time in total.

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