BMS necessary for LiPo pack?

hodgie

10 W
Joined
Apr 5, 2012
Messages
98
Putting 2- 5S Zippies together in series. Using a Imax B6 charger, LIPO sack, low voltage alarms, battery pack placed inside a hard case on the bike and a Watts Up meter to monitor battery pack.

Is it best to attach a BMS to the batteries too? If so, any recommendations?
 
It's not a pack until it has one. It's just a collection of cells.

Will you hear your alarms? Will a B6 ever finish charging? It seems your a long way down the wrong road.

If you buy a bms it will be $20 but postage could be silly, so you should add a much bigger and suitable charger to the bill. Then you won't need a psu to power your charger. A pointless 2 box exercise RC stuff generally expects. Because it's for use in the car, in a field somewhere. The proper approach to building a pack is much tidier. It is just like charging your phone.

You can expect a bill of around $100 for the right bits on your doorstep. Giving about 6 times the charging power, much better protection, and it's idiot proof once assembled. You can keep the B6 for emergencies and use the alarms as door stops.

As your likely in America, Dnmun could perhaps sell you a bms. Might cost you $35 but you would still want a decent charger unless over-night charging of lipo with RC gear helps you sleep better.
 
OK, I appreciate the need for the BMS- getting info/locating one to build your own pack seems a bit like black magic. A little technical advise would be appreciated.

Yes, I understand the Imax B6 will only slowly charge the battery and require extra care - not ready to throw $150-300 at a iCharger until I understand better what this LiPo battery pack maintenance entails. But, I want to take extra care to be safe until I understand the sensitivities and learn the best methods. I watch my Watts Up pretty closely while riding and will put the charger on a timer.

Any direction on the BMS (which RC people rarely discuss) would be nice. Thanks.
 
Yes always a bms is required. But there is such a thing as a human bms. And you are doing that now. Hard to say which type is least reliable.

The most reliable, is an electronic bms, backed up by a human bms.

What I mean is, a bms is not carte blanche to ignore your battery. Having a "you just blew your engine" light in a car is no substitute for checking the dipstick regularly.

Re your charger. Putting it on a timer is no substitute for being ready if a pack catches fire. You don't need a timer, if you are awake while it charges. Your pack is plenty small to charge with a dinky B6. But it's not required to do a full balancing charge every time.

You only need to balance your pack, when it's actually out of balance. As long as no cells are charging much above 4.2v you are ok. But charging to 4.1v will give you lots of wiggle room for being more out of balance. You can do that by using the lilo setting on the charger.
 
Agreed dogman. I watch my Watts Up meter pretty closely - batteries are too expensive for me to do otherwise.

I just don't know anything about procuring or hooking up a BMS for my 2x5S-in-series pack. I want to be safe and do the right things and my budget is very tight. I just can not throw $600 at plug and play pack that might not last a year or not have flexibility for changes in my configuration.

It appears that the BMS is critical to safety and reliability/longevity. Seems a BMS can also be a frustrating point of failure.

I have a lot to learn about the BMS. I just don't know anything about procuring or hooking up a BMS...any insights or link to educational source would be appreciated.
 
This past week I went out of town and forgot to unplug my BMS protected RC Lipo battery pack from the bike controller last time I rode it. Since it was roughly 1/2 SOC (state of charge) the controller idle current drained the battery pack until the BMS detected cell ODDV (over discharge detection voltage) and cutoff, saving all the cells from damage. BMS just paid for itself.

Buying from bestechpower requires MOQ (minimum order quantity) of 2 and I don't like dealing with them. Or, you can find single li-ion or lipoly BMS on eBay with some purchase protections or as mentioned check with user dnum.

I also recommend managing your RC Lipo manually for a while until you're settled on a configuration and better understand how RC Lipo behave. But once you're happy with a pack configuration do yourself a favor and get BMS working with a suitable bulk charger. You'll be glad you did.
 
@Ykick: Thanks for the comments. My goal is to make it as foolproof as possible ...so a BMS seems essential.

Anyone else have a source for a BMS and how to install?
 
you don't need a balancing charger like the icharger if you use a BMS to balance the pack. you can charge using a bulk charger and then the BMS will balance the pack for you. it also provides short circuit protection on the output. and LVC cutoff too.
 
Can you use what you have? If so, you can use a bms already. At the moment your unplugging the battery from the charger, to put the battery on the bike and use it. It involves disconnecting the big wires and the little wires and re-ordering them. The bms version of events is like what you have now, but works 10s so you don't have to re-assemble the pack. Also, instead of taking the cells from the charger, you just unplug the charger from it's psu and take it with you. You don't leave all the balancing stuff at home. You don't rewire it all. You just unplug the charger from the psu and take the lot with you. However, your charger now weighs about an ounce so this is not a hassle.

icharger? your still talking about modeling. You won't find that on an EV site.

Glance this over http://endless-sphere.com/forums/viewtopic.php?f=14&t=56886&p=1009429&hilit=yginrut#p1009429
 
Thank you for your comments!

Very helpful. Anyone else want to chime in?

I saw the SMART BMS posted on the provided thread for $20 but do I need the $200 usb cable for programming? That seems unreal.
 
Need to know how many Amps continuous and peak required before you can do any serious BMS/PCM shopping?

For 15A continuous (30A max) these aren't bad and reasonably priced:

http://www.ebay.com/itm/36V-37V-42V-10S-30A-Lithium-ion-Li-ion-Li-Po-LiPo-Polymer-Battery-BMS-PCB-System-/321660660625?pt=LH_DefaultDomain_0&hash=item4ae4782b91

Many of these vendors can customize so if you don't see exactly what you want, try asking.
 
i doubt if that one is really 30A.

i recommend the Bestechpower D167 for all series up to 20S and 35-40A. it is the best deal for the money imo. too bad you did not get in on the last order. that helps a lot for the shipping and getting just one of them. but i always recommend people buy 2 BMSs at the same time so they have a backup.
 
Thanks again to Ykick and dnnum.. My load is currently a 500W Heinzmanm geared (EVA eBike) that I guess needs about 10A continuous and 20A peak at 36V nominal. But, my future may hold 750W load at 48V which I guess is about the same current flows.

Will the Bestechpower D167 work at 36v/10S?
 
the output current capacity of the BMS is determined by the battery, not the controller. your BMS has to restrict the battery from being discharged at a rate that will damage the pack.
 
So, as usual, its finding the sweet spot between the needs of the load and the supply. My LIPOS will have a 20-25C capability but I am not interested in a high speed racer with my Heinzmann anyway, so, I assume the batteries will not have any problems meeting discharge current needs of the load.. nor will demand currents be high enough to threaten battery life.

By the way, will the Bestechpower D167 work at 36v/10S? I am guessing that even though its nominal design point is 14S-35A at 52V...it can handle 10S at 36V...is that a correct assumption? Does a BMS really care about overall pack voltage? Is it really just looking at individual cell voltages and overall pack input/output currents?

Please advise if I am wrong-headed about any of this.
 
hodgie said:
Thank you for your comments!

Very helpful. Anyone else want to chime in?

I saw the SMART BMS posted on the provided thread for $20 but do I need the $200 usb cable for programming? That seems unreal.

No, you don't need the cable. When ordering they set it up for you. You choose the basic parameters for both bms and charger when you order them. If you were a manufacturer using these boards then you might want the cable. As a one off consumer they will set it for you. I think i linked to an order form. They would want your lvc choice of perhaps 3v. Your hvc of perhaps 42.5v and the fact it's lipo and 10s. Then order a charger with 42v and whatever plug you want on it. Note in the drawing, I show an audio/rca/phono connector added to the boards wiring. This is an option for your charger.

$20 board is ok, but in the drop down menu is a $25 option that supports 20-40 Amps. Well worth the extra $5 because it will run cooler.
I imagine the cheaper 180w charger would be ample. These boards sometimes don't like charging over 4 amps. It's a 5A limit, but a bit inaccurate. The data lead would allow adjustment of such things.

$50 worth of kit, but you will spend another $50 on postage, connectors and wire.

People have talked about buying bigger chargers, set just the same. Thinking one day they could use it on another project. Or it will be less stressed. They have also spoke about carrying a spare. Postage is barely effected.
 
Thanks again freindly1. Great info...need time to digest it all.

In the mean time, I found a BMS primer: http://www.mpoweruk.com/bms.htm to help us Newbies. :eek:
 
friendly1uk said:
hodgie said:
Thank you for your comments!

Very helpful. Anyone else want to chime in?

I saw the SMART BMS posted on the provided thread for $20 but do I need the $200 usb cable for programming? That seems unreal.

No, you don't need the cable. When ordering they set it up for you. You choose the basic parameters for both bms and charger when you order them. If you were a manufacturer using these boards then you might want the cable. As a one off consumer they will set it for you. I think i linked to an order form. They would want your lvc choice of perhaps 3v. Your hvc of perhaps 42.5v and the fact it's lipo and 10s. Then order a charger with 42v and whatever plug you want on it. Note in the drawing, I show an audio/rca/phono connector added to the boards wiring. This is an option for your charger.

$20 board is ok, but in the drop down menu is a $25 option that supports 20-40 Amps. Well worth the extra $5 because it will run cooler.
I imagine the cheaper 180w charger would be ample. These boards sometimes don't like charging over 4 amps. It's a 5A limit, but a bit inaccurate. The data lead would allow adjustment of such things.

$50 worth of kit, but you will spend another $50 on postage, connectors and wire.

People have talked about buying bigger chargers, set just the same. Thinking one day they could use it on another project. Or it will be less stressed. They have also spoke about carrying a spare. Postage is barely effected.

Ok, so I connect my two 5S packs in series and plug the balance plugs into the BMS. Then, connect my power supply TO THE BMS? For some reason, I thought the power supply would be attached directly to the battery power connectors.

Please advise. thanks
 
It’s simple but not exactly easy for 1st time BMS users/installers.

I’m not good with “paint” programs or I’d draw it out but you’ll need to understand how the balance connectors work once the main battery power leads are connected in your desired series count. 2qty 5S = 10S

The deal is you’ll have what seems to be an “extra” or “redundant” balance channel wire because each 5S brick uses 6 pin JST connectors for a total of 12 connections. 10S only requires 11 pins to carry the channel voltages. The +/- cells of where the main power leads connect in series will only need one wire.

I don’t cut or nip anything. I just remove the redundant connector/wire, cover with shrink tube and tuck it out of the way.

Here’s a pic of my 16S1P battery pack assembled from 4qty Turnigy 20C hardcase bricks:
16Sbattery.JPG
Nothing soldered, crimped or molested on the RC Lipo bricks - it's all connectors and moving extension harness contacts to different housings. Here I used a combination of 4S JST extension harnesses and 8S (9pin) connectors to extract the balance channels out to 2qty 8S taps. Again, must account for “redundant” wire between cells #8-#9 (in this case) when connecting to whatever harness the BMS requires.
 
@ykick: thanks for your comments. So I assume the red wire of the balance plug matches up with "1s' pin?

And connecting a 2-5S in series, the "redundant wire is the last wire in the 5S row (the black wire) of each balance plug, so that when you disable them, you have a total of 10 wires/pins connected? Does the BMS plug allow for a "blank/unconnected" 6th pin?

I bet I am missing something here...I will have to think about it.

Also, it appears that for the BMS to control charge/discharge total current, all currents must flow through the BMs....but, how can those small balance wires carry such currents? I don't have a BMS in hand nor have I ever had one to study, so I must sorta guess at how it works.

thanks in advance for your response
 
Ah...Ok....the BMS has separate connectors for charge/discharge current. That makes sense now.
 
Received my first two Lipo zippy 5S/4000 mah packs. checked cell voltage --- one pack has a Cell#5 voltage of only 1.42 V !

So, I assume I must return that pack immediately.
 
Your low cell’s probably gone. Must’ve leaked down on it’s own - probably a leaker. I personally only buy bricks that either commonly sell out and/or turn over frequently as I believe this insures freshest stock and strength in production numbers.

5S 4Ah? That’s an oddball if I ever saw one and I’d only use Zippy brand RC Lipo if somebody gave them to me. Lots to learn… I’m a fan of the 4S Turnigy 20C hardcase. For one thing, if/when one suffers a bad cell it’s only 4S to replace, not 5-6S. Plus, they’re so cheap why not buy a spare or two?

Main power - most BMS accept neg (B-) from the battery and switch that ON/OFF via the neg (-P) or power connection. The ones I use charge and discharge through the same -P connection. Not all do, although Bestepower D167, 140, 245 connect this way.

The balance channel wires merely sense cell voltages and sometimes do minimal 84mA balancing through them. They don’t charge through them - if BMS detects bad voltage range on any cell channel it shuts down the -P main connection. Thus protecting the battery and/or your vehicle/home.
 
Yeah that cell won't be coming back.

Assuming you ordered from Hobbyking, make sure you register the warranty codes for your Lipo packs (option on the Customer Service tab when logged in to your account).

Also take a photo of the voltmeter measuring the cell as proof.
 
The Smart bms must have the main wires hooked up before the balance leads are connected. This is very important. You can't have the balance wires connected if the board is not powered. It will smoke. The balance plug should also be inserted so the lower numbered cells get power first. So 0-5s pack first, then the 6s-10s pack.

In my link I did as Ykick describes, and took out the redundant balance wire. It's coloured red. The pics explain it, but I didn't. I did it by using an extension harness and chopping that up instead of my bricks. In fact... Yes I thought as much: http://www.ebay.co.uk/itm/3dRCparts-JST-XH-10S-TO-2-5S-BALANCE-SERIES-SERIAL-ADAPTER-LIPO-CHARGE-CORD-/380834742673?pt=LH_DefaultDomain_0&hash=item58ab850191
That will turn a pair of 5s into a 10s.
Your likely to want a bit of power cable and some banana plugs to match your cells. Making cell changing plug n play. You might find it easier to buy leads and chop them up, than buy separate cable and plugs to assemble yourself. Some soldering would be needed though.

The boards are proven to 65 amps for longer than your pack would last. That required some extra heat sinking, but they are by no means exaggerating their claims.
 
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