I've made up my mind to put it in the center even though that requires the most work. You ever notice the best placement or best way of doing something usually requires the most effort? Here I'm going to have to do a little cutting and relocating to make it fit. It's 1/4 of an inch wider than the original batteries and about 2 inches shorter in length. It's also several inches taller because that was the size of the material I had to work with. But the height is not any issue. That 1/4 inch wider is an issue. lol I could have made it that 1/4 inch narrower but I wanted a little air space between the sides of the box and the battery for cooling air to pass through and to keep the cold from seeping through in winter. Anyway now that I know where it's going I am able to start mounting the electronics. Some of the parts won't be here until tomorrow though. Like everything this sure got complicated!
From some documentation on a BMS for use with lithium-ion cells in a cordless drill: Starting a cordless drill motor may take 42 to 56 amps.
Considering that the golf cart has a MUCH bigger and more power-hungry motor, a pedal-to-the-metal start could probably peak at 200 amps or more. Be gentle on the accelerator and you shouldn't encounter a problem. If the BMS shuts down from a hard start or a heavy load, hit the reset (or use the app) or disconnect the BMS from the battery to reset the overload (pull the balance connector, disconnect either positive or negative battery cable) if removing the load doesn't get the reset. As yet, I haven't overloaded any lithium-ion or LiFePO4 BMS badly enough that it didn't recover after simply removing the load.
Made more progress on the battery box today. You know the kind two steps forward and three steps back. Anyway I got the 48 volt to 12 volt converter mounted on the outside. Both the heating and cooling thermostats are mounted and the heating pads are in and all wired up. Come to think of it the fan is also wired but not yet mounted. I may have to order something different for a fan. The 12 volt fuse / power distribution block is mounted and wired. I also installed a ground stud for all the 12V stuff. The 300 amp circuit breaker is mounted.
I pulled the buss bars off and rechecked the balance of the cells and they were all over the place and I have NO idea why. The lowest one was 3.33 and the highest one was 3.65 and everywhere in between. I have them all hooked in parallel to rebalance them. Looks like I will be keeping a SUPER close eye on them until I A) get a BMS or B) find out it was a fluke. IDK what the heck caused them to go so far out of balance! All I've done so far was to run them down about 60% and recharge them once.
Balance is important for series cells - especially any flavor of lithium. However, there are now "balancers" for lead-acid batteries in series (36 volt and 48 volts golf carts ring any bells?) because they also last longer when the cells are equalized and they all handle equal amounts of the load. When you have a wide range of cell voltages, it's possible for a cell with low voltage to be driven to reverse polarity which A) can damage the cell and B) can be a fire hazard. There are good reasons that even my small lithium packs, such as the 3s2p 18650 lithium-ion pack for the hand vacuum, all have a BMS. Obviously, having very unbalanced cells can lead to shorter battery life so that's as good a reason as any to have a BMS in place as soon as possible. I did the "all cells in parallel" balancing of my small LiFePO4 packs but I did not put any of those packs in service until they had a BMS. I see the golf cart as "severe service" for a battery and I would consider a proper BMS the most needed accessory.
Question for you Papa. I inherited a couple Fluke meters some while back. With all this battery stuff going on I decided to dig them out. Got new batteries in and the multi meter reads different than my trusty old NOT CHEAP HF multi-meter. I bought their most expensive unit many many years ago and have used it since. Now this Fluke meter is probably about the same age but Fluke is supposed to be one of the best if I'm not mistaken. How can I find out which one is correct? My old HF meter reads these cells at 3.37 - 3.38 and the Fluke reads them at 3.412. I KNOW .04 of a volt isn't that great a difference but I would like to KNOW not guess. Any ideas?
Didn't you know? A man with one watch knows what time it is. A man with three watches is never quite sure ;-)
You need a way to check the calibration of the meters. There's an inexpensive device, based on the AD584 chip, that provides accurate voltages at 2.5, 5, 7.5 and 10.0 volts, The better devices come with a traceable-calibration printout of that device's output voltages. Something like this:
AD584L verified calibration
Nominal Output Actual Voltage 2.5V 2.49936 (0.00064V low) 5.0V 4.99871 (0.00129V low) 7.5V 7.49805 (0.00195V low) 10.0V 9.99668 (0.00332V low)
That does assume you've let the device run long enough (10-15 minutes) for the AD584 chip to stabilize and the device needs 12-24 volts (two 9 volt batteries in series work OK, some have a battery holder for the 12 volt battery used in remote controls, for a few dollars more you get a plastic case and a rechargeable battery). As you can see from the example chart, the calibrated output is more accurate than any of your meters. I'll hazard a guess that the Flukes are more correct but some of the older HF meters had a calibration pot on the board so you can adjust the 20 volt scale to read correctly at the 10.0 output of the AD584 and be comfortable that the meter is as accurate as you can set it - that may take some time as the calibration pot needs only a small adjustment when you're working on 10.000 volts :-( Or you can read the voltages from the AD584 and make up a "correction chart" like the one above with something like "meter reads 0.002 high at 5 volts" or "meter reads 0.003 low at 2.5 volts" and just remember to include the correction in the voltages you read.
Way over my head Papa. But after talking to another fella who knows this kind of stuff also, I decided to just go with it. Point 04 of a volt at 3.5 volts isn't really very significant. Just to be safe I'll go with the highest voltage reading.
Looks like I'll be ordering a BMS tomorrow after I drop some cash in the bank. I don't keep any money in the bank over the monthly bills, life long habit don't trust what isn't in my direct control.
Because you have a 36 volt rated motor and you're running a 48 volt battery pack and you've seen 90 amp instantaneous readings, I'd say go with the 250A BMS - unless you plan to put a separate BMS on the second battery, in which case each battery should be OK with a 150 amp BMS. But I tend plan electrical/electronic things on the conservative side.
The maximum continuous load that the solar backup system is configured for is 1350 watts but I have a 2000 watt pure sine wave inverter (plus a spare). On the other hand, everything has seen almost 5 years of as-needed service with no problems other than the batteries aging - not something I can fix until I have $$$$ for LiFePO4 batteries (maybe next time they're replaced?) - and near-by lightning taking out the USB ports on the laptop used to monitor the solar system (twice) but no damage to the solar equipment itself. One of those near-by lightning hits took out both HDMI ports on the 50" TV but all the equipment has "component" ports (RGB video plus audio) so $50 for cables and a manual switch box and all is well.
I think 840AH (3*280) or 1120AH (4*280) of LiFePO4 at 12 volts might be a good plan for the future of solar power. With a 2000 watt load on the inverter, the input current would be just under 200 amps (85% efficient), so each 280AH battery bank would be fine with a 100-150 amp BMS because each battery should never see more than a 100 amp load. In household backup service, the appliances can be put on digital timers so that power to each higher power device (fridge, freezer) is in alternate 2 hour segments - fridge 2P-4P, freezer 4:10P-6:10P, fridge 6:20P-8:20P, freezer 8:40P-10:40P, etc). That will keep both units cold but both will not be starting their compressors or running their defrost heaters at the same times. The fridge is rated to maintain a safe temperature without power for 8 hours with the door closed and the freezer for 16 hours, so 2 hours without power should not be a problem for either. That project has a lot of research behind it ;-)
Last Edit: Jun 12, 2022 13:56:03 GMT -6 by papaof2
Got the BMS ordered. I fought with myself bigtime on this one and ended up ordering the 250 amp BMS. It cost twice as much as one that more than likely would have done the job just fine. But I know this one should be able to handle more than I could ever throw at it with my battery and motor setup or any other motor I may possibly get in the future. Hopefully it will last as long as the battery cells should! Bad thing it could be up to 6 weeks or more before it gets here. UGH the slow boat from you know where!
I just added up the total battery cost ouch! It did however come out to be almost exactly the same as buying lead acid batteries. Still it was more than I wanted to spend. Lead acid replacement batteries were actually one dollar more without tax over what I paid including tax.
Last Edit: Jun 13, 2022 9:01:28 GMT -6 by biggkidd
Lithium iron phosphate batteries usually are rated for approximately 4500 to 5000 charge cycles with an impressive 80% depth of charge. If you plan on spending one charge cycle each day, the battery is meant to last over 12 years.
If your daily discharge is less than 80%, you can expect the cycle life to increase by some amount - and that cycle life is typically to 80% of the battery's original capacity (your 100AH battery is now 80AH - condidred end-of-life in commercial use). You might get another 500-1000 cycles before reaching 60% of original capacity (your 100AH battery is now 60AH). That should cover the lifetime of two or three sets of lead-acid batteries.
A possible future story has someone waiting on electronics coming from China "apparently by rowboat" ;-)
I ordered two things from vendors in CA. One came USPS Priority Mail (4 days). The other came UPS Ground (7 days). For all the bad things we say about USPS, they did beat UPS on a shipment of similar size and weight. I don't know about the cost as both were "Free Shipping".
Last Edit: Jun 13, 2022 14:07:36 GMT -6 by papaof2
I agree whole heartedly. I hope they will last 20 years or more the way I should be treating them. The voltage is a little higher and the voltage curve is a WHOLE lot flatter through most of it's range. Where lead acid drops down through 50 in to the 40's fairly fast these should always stay up around or above 50 volts. With the curve they have it wouldn't surprise me to be able to keep the voltage above 52 with just the one panel on moderately sunny days. Ideally I will be able to keep the voltage in between 52 and 53 volts all the time.
Last Edit: Jun 13, 2022 14:40:09 GMT -6 by biggkidd
Proper care is the key to battery life (any type of battery).
I replaced the previous set of AGM batteries on the solar backup system just before they reached 9 years old. With a typical AGM life of 5 +/- years, I did OK ;-) The battery I replaced in my truck abiut 2 years ago was 5 1/2 yers old and I replaced it because to my ear the starter turned a little slowly for a warm day. Some time on a slow charger with a desulfator and that battery now tests at 90% of new. If I need a battery for either vehicle in a hurry, this old one is "good enough" until I can get a replacement and it makes a great source for testing power inverters and the like.
It's time to junk the basic Group 24 battery I picked up (free) in 2006 (date code is 2004). After long service as a source of power for testing 12 volt lights, radios, fans, fridges, power inverters and battery chargers, the battery has finally given up the ghost. It's 18 years old so I'd say it had a long useful life ;-)
Last Edit: Jun 13, 2022 15:09:31 GMT -6 by papaof2
Some meters are easier than others. If I remember correctly, it's three or four button presses to clear the meter I have and another couple of button presses to get it back to normal display - something that probably should be on a laminated card so it can live next to the meter...
Remembered to check it tonight, it took 20 amp hours to go up with one passenger and back with two. That's 4 miles round trip and I wasn't being easy on it. Wasn't being hard either just driving kinda like I had somewhere to be.
That works out to an average of 5AH/mile. If you plan to stay within the 80% discharge of one battery, that's about 80AH / 5AH/mile = 16 miles total range - two batteries would give double the range. Just be aware that cold weather or heavier loads will decrease that number (even more decrease for cold and heavy).
Almost as good as one of the VERY cheap Chinese "commuter" cars that has a top speed of 25MPH and a range of about 30 miles (probably from aliexpress.com) - but it did have doors and winshield wipers ;-)
What it really told me was that I can use the cart A LOT more than I thought. We already knew a days chores used about 1/6th of the battery power. This means I can use it for more pleasure trips and just going riding more than I thought. With it being nearly silent it's a lot of fun to ride and watch animal life. I got within 20 feet of a black bear on it the other morning and had to ask him nicely to move so I could go by. He got up from where he was sunning himself and ambled away. He knew I was no threat and I knew the same about him.
I am going to start looking for a more economical operating system for it. Not so much to save power but that's always nice too. What I want is to be able to ride a bit slower a lot of times. The lowest throttle setting on this is often three or four times as fast as I want to go. As it sits now the low setting is still faster than a fast walk, maybe a good jog. I will CAREFULLY remove the system in there as intact as possible so if I ever need to put it back it won't be an issue.
I pulled a few logs with it this morning nothing real large with the largest being about 8 inches on the big end and twenty feet long. I can officially say it pulls them a whole lot better and easier than a garden tractor does. Changing the batteries out for a single lighter battery will probably reduce that ability by reducing the traction weight. Which is no issue as I have several better ways to move larger things. But I do enjoy the quiet and lack of diesel smell. All in all this thing is a whole lot more capable than I ever dreamed possible.
Last Edit: Jun 14, 2022 10:19:23 GMT -6 by biggkidd
Remember the original design - carry four fat guys and 400+lbs of golf clubs because they can't possibly carry that much weight across a 16 hole course. And do that as many times as possible on a sunny day - except in the Lake District of England where we saw people playing golf in pouring rain...
In order of delivery time reliability in my experience:
Amazon - usually within a day UPS - usually within 2 days USPS - package could be waiting in a trailer for days - coded as "Departed xxx facility" because it left the building DHL - sometimes doesn't know where things are or even that it has a package with that tracking number FedEx - up to three weeks later than estimated - see notes below
I had two orders of lithium batteries that each took 3 weeks from FedEx's local distribution hub to my door. One order listed as "Delivered, signed for by MM" but we don't have a neighbor with initials MM. That package "magically" turned up on the porch three weeks later. The other order had "Not delivered - weather" among other reasons for delay but the rain that day ended before they loaded the trucks! I told one vendor to not ship to me by FedEx as they weren't competent to deliver anything.
Got to watching an old movie last night and while I was at it I went ahead and put the cells in the battery case. WoW talk about a perfect fit. I used some 1/8th" high density foam mat to sandwich the cells tightly inside the box, one piece on each end. The foam was packing material from the lift kit. lol None of the cells actually touch the case anywhere. Lord help me if they ever need to come back out they are in tight. I still need to figure out some way to lock them in place side to side where there's a 1/4 inch gap between the cells and walls for airflow. If anyone has any ideas I'm all ears. I also need to maneuver them a little to get the aligned properly. Again No idea how as tight as they fit.
Last Edit: Jun 18, 2022 8:32:14 GMT -6 by biggkidd