DIY Lithium Packs, Proposal and Discussion
- Thread starter luthj
- Start date
shade
Well-known member
What's the harm in breaking temperature management out of the BMS, adding a layer of redundancy?
Have the BMS set up to monitor temperature via a discrete probe, with an alarm enabled as well as charge disconnect. A standalone heating system would be easy for a clever fella to create, and using a separate probe would give you an important double-check on that parameter. Not quite as sexy as an all-in-one solution, but this seems like a good place to not have full integration.
Have the BMS set up to monitor temperature via a discrete probe, with an alarm enabled as well as charge disconnect. A standalone heating system would be easy for a clever fella to create, and using a separate probe would give you an important double-check on that parameter. Not quite as sexy as an all-in-one solution, but this seems like a good place to not have full integration.
luthj
Engineer In Residence
Okay, slowly narrowing down on what I want (for now).
Here is a rough breakdown. I will reuse most of my existing gear, shunt, fuses etc. This will yield 400AH @12V nominal. Discharge at 400A, and charge at 200A if necessary. Pack will have BMS controlled heaters and an insulated box (removable lid/vent for warm weather?). Pack will have a single master disconnect contactor, which will be emergencies only. There will be a visual caution and audible alarm output on the BMS. The orion BMS has extensive self checking routines, including redundant temp sensors, and it will drop out and alarm if the voltages from all the inputs don't jive. If it locks up and goes dead the system will drop the main contactor. The charge sources will all be configured to absorb for a short period then end the charge. Except the alternator. I already have a ACR, which can be manually controlled. So I will just wire that to the charge control output of the BMS.
As far as failure tolerance goes, I tend to favor a single high quality system with integral monitoring. A single alarm/light will hopefully show any issues. I can configure my outback system monitor to trigger an output at low/high voltage for the pack, and I will probably do that as a backup. In fact I may configure the main contactor, so that if either the BMS or the Mate detect an error (over/under voltage etc), that it will not engage.
The advantage of a central monitoring is that the user doesn't need to check multiple sources for relevant information. Of course its a central failure point, but so is most of the wiring. A single loose connection can take a pack out just as easily.
Cost wise I am about 1000$ under 4x battleborne drop-ins. I do have direct access to the BMS, and I can fix things if they break. Its not a huge gain over the drop-ins cost wise.
Here is a rough breakdown. I will reuse most of my existing gear, shunt, fuses etc. This will yield 400AH @12V nominal. Discharge at 400A, and charge at 200A if necessary. Pack will have BMS controlled heaters and an insulated box (removable lid/vent for warm weather?). Pack will have a single master disconnect contactor, which will be emergencies only. There will be a visual caution and audible alarm output on the BMS. The orion BMS has extensive self checking routines, including redundant temp sensors, and it will drop out and alarm if the voltages from all the inputs don't jive. If it locks up and goes dead the system will drop the main contactor. The charge sources will all be configured to absorb for a short period then end the charge. Except the alternator. I already have a ACR, which can be manually controlled. So I will just wire that to the charge control output of the BMS.
| Item | Qty | Cost | Total |
| Orion Jr BMS | 1 | $ 450 | $ 450 |
| 100AH Frey Cells | 16 | $ 100 | $ 1,600 |
| Blue Sea 7713 Contactor | 1 | $ 200 | $ 200 |
| Cell connectors/Misc wiring | 1 | $ 200 | $ 200 |
| Heating pads | 2 | $ 100 | $ 200 |
| Box materials/Insulation | 1 | $ 100 | $ 100 |
| Grand Total | $ 2,750 |
As far as failure tolerance goes, I tend to favor a single high quality system with integral monitoring. A single alarm/light will hopefully show any issues. I can configure my outback system monitor to trigger an output at low/high voltage for the pack, and I will probably do that as a backup. In fact I may configure the main contactor, so that if either the BMS or the Mate detect an error (over/under voltage etc), that it will not engage.
The advantage of a central monitoring is that the user doesn't need to check multiple sources for relevant information. Of course its a central failure point, but so is most of the wiring. A single loose connection can take a pack out just as easily.
Cost wise I am about 1000$ under 4x battleborne drop-ins. I do have direct access to the BMS, and I can fix things if they break. Its not a huge gain over the drop-ins cost wise.
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shade
Well-known member
If the BMS module failed, would you be comfortable doing full-manual charge management until you could install a replacement? If so, I can see some value in a standalone heating system that would still be operable even if you had to go with manual charging. I know it's unlikely that you'd find yourself managing the system with a multimeter and a kitchen timer, but it's a possibility. Just a thought.
But IMO far superior, more flexible.
I question the "Frey" cells, what is your basis for that choice?
Also why 4P as opposed to going to a bigger size?
Orion is a well respected BMS. Include the ability to disconnect everything from cells, so can be fully isolated when unused.
I question the "Frey" cells, what is your basis for that choice?
Also why 4P as opposed to going to a bigger size?
Orion is a well respected BMS. Include the ability to disconnect everything from cells, so can be fully isolated when unused.
luthj
Engineer In Residence
Its a consideration. Since my pack will be inside the vehicle, the heaters are most a backup. But a spare thermostat isn't expensive or large. In theory the BMS won't even be necessary. At my typical charge/discharge rates, I should be able to get 100+ cycles without any need to balance (if I stay out of the knees). And the chargers are sufficiently configurable to prevent overcharging with conservative settings.
Part of the reason is redundancy. If I loose a whole cell group (4 cells), I can reconfigure for 3P or 2P at reduced capacity.
Some of my previous reading indicates that prismatics over 100AH are not as robust with regards to vibration.
Part of the reason is price. They are a tier B MFG, but appear to do many thousands of batteries per run, and offer factory test reports with their orders (that's what I have been told). They sell direct to US buyers via airmail. I am still looking at other cells, and if I spot a good deal on some CALB or similar cells, I will jump on it.
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shade
Well-known member
Good point. If the BMS died, whatever rewiring you'd have to do to get by without out it wouldn't be made much more difficult if you had to do the same with the heaters. If the Orion is smart enough to recognize an internal fault and shut everything down, the redundancy of a standalone heating system loses some of its value.
More an observation, but I've seen some systems that seemed to have been intentionally designed around their BMS disconnecting the battery during regular operation. I think that's asking for problems that could be avoided by properly sizing the battery to the expected loads, and using charge controllers that are smart enough to shut down before reaching an overcharge state, as you described. I know these systems aren't cheap, but spending more up front for the required capacity and better controls makes more sense to me than leaning so heavily on a BMS.
Or maybe 1000+, with good quality well matched cells. At 1C discharge rates, maybe not, and do stay under 0.3C charging when temps get cool.
> And the chargers are sufficiently configurable to prevent overcharging with conservative settings.
Additional HVC is for when those fail.
> Some of my previous reading indicates that prismatics over 100AH are not as robust with regards to vibration.
I don't think that kicks in until 300-400Ah, if it's true at all.
But yes, redundancy is good. Just do no more than 2 top-level strings, just one even better, 4P at the lowest level.
> if I spot a good deal on some CALB or similar cells, I will jump on it
If you'd like the bank to last a decade or more, I think that will greatly improve your odds. Personally I would not buy a brand without numerous user kudos over at least five years.
Others on my shortlist: Winston/Thundersky/Voltronix, CALB, GBS, Sinopoly and A123 (now Lithium Werks)
Factory direct or a well trusted vendor is critical, lots of fraud out there, secondhand sold as new, QA rejects, etc.
Not recommending these specific cells over the ones I mentioned, but check out how they compare to those Freys.
This guy's been around a while, spotless seller record and eBay's pretty foolproof enforcing its NQAMBG, long as you do thorough testing on arrival.
If 60Ah is right, 300Ah @12V
3.8kW at $350 each
LiFePo4 cell s 60ah 3.2v Lot of 20pcs lfp life battery lithium | eBay
NOS 60ah cellsTested @10a => 60ah.
www.ebay.com
This guy's been around a while, spotless seller record and eBay's pretty foolproof enforcing its NQAMBG, long as you do thorough testing on arrival.
If 60Ah is right, 300Ah @12V
3.8kW at $350 each
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luthj
Engineer In Residence
Thanks for the tip, I will give it a look. Having 5P would complicate the layout a bit, bit should be doable.
I am sure john noticed over on sprinter source, but this china source claims 8x CALB 180AH cells for US $1,170.00 delivered. Which is a very good price if they are legit.
I am sure john noticed over on sprinter source, but this china source claims 8x CALB 180AH cells for US $1,170.00 delivered. Which is a very good price if they are legit.
Yes those kW are only $250, and getting CALB, supposedly **factory fresh** Grade A!
Calendar life is a significant factor in long-term value.
But, if you had a bad batch or even just a few lemons - and even with top vendors they can slip through - it's just not cost-effective to ship back to China for the warranty claim, you'd have to eat the loss.
Some say worth the risk with the pricing so low. . .
I really prefer dealing with a NA-based seller.
Worth getting a quote from Voltronix for Winstons maybe?
Calendar life is a significant factor in long-term value.
But, if you had a bad batch or even just a few lemons - and even with top vendors they can slip through - it's just not cost-effective to ship back to China for the warranty claim, you'd have to eat the loss.
Some say worth the risk with the pricing so low. . .
I really prefer dealing with a NA-based seller.
Worth getting a quote from Voltronix for Winstons maybe?
Another immaculate-rating seller, has done dozens of these 4-lots, only posts one at a time, always at the same price, $330/kW delivered
LiFePO4 12V 100Ah Lithium Iron Phosphate Deep Cycle Battery | eBay
Capacity = 100Ah. I also have extensive experience qualifying and testing lithium batteries. This battery was manufactured about 2 months ago. Cell weight: 2.85kg.
www.ebay.com
Here is the supplier I used on Alibaba, another source to compare with. I purchased the 180Ahr CALB cells. Have not done a capacity test yet, planning on it thou.
hhpower.en.alibaba.com
Dongguan Huanhuan Energy Technology Co., Ltd. - 3.2 V120AH Lithium Battery, Rv Lithium Battery
Dongguan Huanhuan Energy Technology Co., Ltd., Experts in Manufacturing and Exporting 3.2 V120AH Lithium Battery, Rv Lithium Battery and 187 more Products. A Verified CN Gold Supplier on Alibaba.com.
hhpower.en.alibaba.com
hour
Observer
Chinese bms + arduino/esp8266/esp32/etc? Think my 60a Chinese bms has external relay output but I don’t know how to operate it as I haven’t used their official chinglish app.
but Pretty sure lithiumpcb dot com site will customize your bms if needed.
maybe I’m missing something but couldn’t a Chinese bms + arduino give you the capabilities you seek?
but Pretty sure lithiumpcb dot com site will customize your bms if needed.
maybe I’m missing something but couldn’t a Chinese bms + arduino give you the capabilities you seek?
luthj
Engineer In Residence
I think it could. I am just trying to balance my own time investment. Both in initial setup, and in the monitor/prove testing phase. As much as I would enjoy another project, I need to be realistic about my long term goals (and all the other things life throws my way).
I am not ordering parts right away. I need to get my 4wd conversion 90% finished before I jump down that rabbit hole. So it will be a few months.