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Post by papaof2 on May 26, 2022 18:33:36 GMT -6
You're missing two things - the battery's maximum discharge current (300 amps for 30 seconds) and the cart motor's maximum amp drain. One BMS shuts down around 80 amps after 7-13 seconds and higher currents shut it down faster - just a few milliseconds at 200 amps. The motor's max amp load is needed to choose a BMS that works well with the load being powered. Like a fuse, the BMS needs to be able to handle the maximum amps needed in expected use. Link to battery specs: cdn.shopify.com/s/files/1/0481/9678/0183/files/LF105_3_2V_105Ah_Product_Specification_Version_F_1.pdf?v=1641491228You need a clean, dry place to bolt the BMS to metal for heatsinking. If the battery compartment is waterproof and dustproof, it will work. If not, maybe some time with epoxy or duct tape to seal up that compartment as it no longer has liquid electrolyte to spill or hydrogen gas to dissipate? Or come up with some other large, clean, dry metal surface to be the heatsink. Among the BMS units you found, only the VNSZNR lists the board as waterproof and dustproof. The others may have those features but the Amazon ads don't mention it. Quite often, you need to find the manufacturer's datasheet to get that bit of info as many sellers assume the BMS is going on a solar installation that's in conditioned space. The big DALY BMS units seem to get high praise but the largest BMS I've had hands-on with is an unbranded 40 amp lithium ion BMS for use in updating a nicad battery drill to lithium ion cells. Any decent BMS in that size range should have temperature controls and the ability to set charge and discharge voltage levels.
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Post by biggkidd on May 26, 2022 18:48:40 GMT -6
The average continuous amp draw is 15, 30-40 when taking off with a spike up to 90 ONCE taking off pedal to the metal up hill with 4 people in the cart on the steepest hill around here. Otherwise it almost never sees over 50 amps. I was load testing it to see what I needed for new batteries that's how I decided on the 105AH.
Glad you refreshed my memory about heat sinking, thanks!
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Post by papaof2 on May 26, 2022 19:45:02 GMT -6
If you've seen 90 amps, I'd guess the peak amps - something most meters can't keep up with - are 1.5 or 2 times that. I would get a BMS in the 150 to 200 amp range unless you have access to an oscilloscope and a 200 amp or bigger meter shunt to be able to measure those peaks - or never go full throttle or be caught going up a hill with a heavily loaded trailer where the extra load and the higher motor current just "sneak up" on you.
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Post by biggkidd on May 26, 2022 20:11:24 GMT -6
Thanks Papa I'll do some more checking around.
90 was just a flash on the screen through a 300 amp shunt it fell back under 40 in way under a second. Some of the LifePO4 "golf cart batteries" use the same cells and two of the three listed BMS's, and also other brands BMS's I'd expect. There are several brands with a 100-105AH setup "designed" for golf carts using these parts. They also make 48AH and 54AH up though 300AH. The BMS is usually closely matched to the AH rating of the battery from what I've seen when it comes to golf cart batteries.
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Post by papaof2 on May 27, 2022 9:15:21 GMT -6
The BMS *should* match the battery BUT the BMS needs to be able to handle the motor's peak current which can only be measured with a peak-reading meter or an oscilloscope. That battery's "300A for 30 seconds" is probably more than adequate for the cart but the problem would be having the cart in a bad place and the BMS limiting you to much less current than the motor needs at that place - not something that most BMS specs provide details on as their focus is often on solar power applications where the maximum load current is easily measured or calculated. DC motors are a different animal, being seen as almost a dead short across the battery when the motor is at rest.
I don't know if any BMS maker has one aimed at golf cart use. Maybe a search for "golf cart BMS"? I'm currently between an appointment with the pain clinic (another injection in my back is now scheduled two weeks out, with more invasive procedures discussed if the injection doesn't work) and a haircut (one of the few things I can't do for myself ;-)
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Post by biggkidd on May 27, 2022 10:38:40 GMT -6
Sure hope you feel better. Thanks for all your help!
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Post by biggkidd on May 28, 2022 14:43:57 GMT -6
Had a fraying cable end on one of the main power wires going to motor from the forward / reverse switch I finally got around to replacing it last night. After noticing the wire insulation was starting to melt from inductive heat. Oops! I need to replace the cable someone used 6ga were 4ga was and 2ga should be in my opinion.
The interesting part is we are now getting totally different Amp readings much MUCH higher readings. In the cart by myself up a steep hill and it was pulling 145 amps under full power. That same hill is where we did a test from stopped with 4 people and it only showed a 90 amp draw for a split second. Not sure how that was affecting the meter but obviously it was. It was also cutting the power some it feels more responsive than it did and didn't seem to slow nearly as bad on the hills today either. Now going down the road in more or less level spots instead of showing 15-30 amps like it has been it's showing 45-75 amps. I guess that connection was a lot worse than I realized!
Looks like I will not be using a 100 amp BMS. Debating running a BMS at all I see a lot of folks don't and self balance the cells every few months if needed. I'm thinking that may be the way I go. Wish I had these numbers BEFORE I ordered cells. I probably would have saved a bit longer and bought larger cells.
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Post by papaof2 on May 28, 2022 16:36:33 GMT -6
Your frayed cable was acting as a resistive speed control - just one that wasn't designed for the purpose :-( When you're moving a lot of amps, you need to be sure that the wiring is the right size for the length of wire needed, is in good condition, is properly terminated (good crimps or soldered terminals) and that the bolts/connectors are correctly tightened. One set of batteries that I used with the solar backup system had threaded inserts and used M6 bolts for connections. That meant getting an inch-pound torque wrench to ensure I had the bolts at the proper torque. I used one of the IR thermometers (under $30) to check all the equipment, wiring and connections when I put the system together - and then repeated that check about an hour in on the first long run. The wiring for the 2000 watt inverter is 4 gauge between batteries and to the 200 amp breaker for the inverter. Wiring from the breaker to the inverter is the two wires for each feed (positive, negative) as provided by the manufacturer. With a maximum continuous (more than just startup) load of 1350 watts, the inverter draws 1350 watts / 0.85 (efficiency) / 12 volts = 132 amps. 4 gauge THHN wire is rated for 95 amps continuous in AC wiring (house/commercial service). Marine (boat) wiring at 12 volts allows using 4 gaude for up to 160 amps at 10 feet if a 10% voltage drop is acceptable. I'm using perhaps 2 feet of wire in the battery connections and the average load is much less than the 1350 watts maximum load so 4 gauge is more than adequate in my usage. I did a lot of reseach on this because I sleep in this house, even when the backup system is in use. Marine wiring specs here: www.westmarine.com/WestAdvisor/Marine-Wire-Size-And-AmpacityWith the cart being outside, having the BMS provide temperature protection when charging/discharging is a good idea - you don't charge most LiFePO4 below 32F and they may have a discharge temperature limit: check the battery datasheet. I'd say a 200 amp BMS to handle the motor's needs when loaded with people or cargo, towing a trailer or going uphill - or some combination of that - but it would be better to have the locked rotor specs for that motor. Is there a maker name and a model number visible? Building your own - solar power of any size, waterwheel generator, whatever - provides an education and most education has a price :-( If I could have seen just a few years into the future, my solar backup system would be 48 volts and have a 4000 watt (or bigger) 120/240 volt split phase inverter so it could power more things. However, most of the pieces I got as the system grew have been incorporated in the current system or they are part of a fallback design if lightning or whatever does major damage to the system. Everything purchased is just part of the cost of your education. You can only speak knowledgably of the effective lifetime of a given battery type if you have used that type battery until is reaches "end of life" or you have access to published life testing data. I'm aware that the AGM battery bank for the solar backup system is beginning to show its age - the daily power used to maintain the bank at float voltage has slowly increased from 30WH to 50WH - not much power but it is a change from one year ago so I need to be aware of it. I don't plan to replace the batteries for several years - they're for backup, not daily prime power - so there's no rush to replace them, just a push to find a good deal on LiFePO4 replacements. Based on the power needed at maximum load (other than startup power), a LiFePO4 battery bank might consist of four 100AH batteries with appropriate BMS connected in parallel for 400AH. If funds at that times are adequate, upgrading to four 280AH batteries in parallel would increase the run time to 1 1/2 days (with freezer and window A/C but with zero sun). Without sun, it becomes a "Charge once daily" backup system that provides silent power for 30 hours on a 6-8 hour run of the inverter gen to recharge the batteries. If there is sun every day, 1500 watts of solar panels would keep things going for almost three weeks without using the generator. With 1500 watts of solar panels and using the gen once a week, the backup system could provide "forever" power at the "cabin in the woods wth a fridge" level of power. In a long term outage, that might make us the "richest" people in the neighborhood - or the primary targets...
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Post by biggkidd on May 28, 2022 20:07:22 GMT -6
You are right about that and believe me I have paid for every ounce of what I know. Little as that may be. lol
I'm thinking I'll order XX feet of 2ga and make my own cables after I get a few other things finished. Over the years I've gotten pretty good at making up cables. I use copper pipe for ends. Cut a peace of pipe just large enough to fit the bare wire in crimp the end flat with the wire flush to the end. Then solder it and drill your bolt hole. Makes a really good and cheap connection. Top it off with a little heat shrink if you desire. Best of all the bolt hole fits whatever your connecting to. I got tired of oversize bolt holes on terminal connections.
Spent a few hours working on a front end extension and bumper. It's a combo deal. I want a bumper out in front of the tires a little. I also want more storage space and carrying places. So this will extend the front about 1 foot and let me make a box or rack or something to put things in.
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Post by papaof2 on May 28, 2022 20:50:38 GMT -6
If the cart was 3 feet longer, you'd still need to add storage space ;-)
Don't you know that stuff expands to fill 120% of the space available?
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Post by biggkidd on May 29, 2022 7:08:05 GMT -6
If the cart was 3 feet longer, you'd still need to add storage space ;-) Don't you know that stuff expands to fill 120% of the space available? Yep there is NO doubt about that fact! lol
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Post by biggkidd on May 29, 2022 13:52:16 GMT -6
My new LifePO4 battery cells arrived sooner than expected! Right when the store said they would! I got them from. www.18650batterystore.com/collections/lifepo4-prismatic-cells/products/eve-lf105They come very well packaged! I would say chances of damage occurring in shipping are minimal! This is the only one I've opened so far but as you can see they look perfect! Should I do a separate thread on the battery build so it can be found easy? Darn the pictures didn't come through they are to large being over 1MB
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Post by papaof2 on May 29, 2022 15:41:14 GMT -6
The forum's image storage was exceeded some time ago. Lots more room available for text postings than for PDF files or pictures :-(
Try one of the free online storage sites and then provide the link to the picture.
Separate thread is possibly easier to locate with a search but continuing here is fine.
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Post by biggkidd on May 30, 2022 9:19:30 GMT -6
Oh well.
Tested all the cells last night they all were 3.25 or 3.26. Hooked them all in parallel to balance 100% . This morning unhooked them and now they all bounce between 3.25 and 3.26. lol Wired them up in series and got 52.2 volts and put them on to charge. At 11 am they were up to 52.5 going to 57.7 to 58.4 with 58.4 being absolute max charge for this first cycle or two after that they will never see voltage that high again as long as I own them. I plan to setup my charge perimeters somewhere down to around 51.5 up to 53 volts. Keeping to that sweet range.
ETA: If I can keep them in the 52.00-53.00 volt range even better!
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Post by papaof2 on May 30, 2022 14:22:08 GMT -6
3.65 volts/cell is the "standard" charge-to voltage for LiFePO4 cells, at least from the manufacturer's datsheets I've read, with 4.1 volts/cell being the absolute maximum. 3.55 volts/cell seems popular with many users. I'm testing much smaller cells (3.8AH) but charging to 3.55 volts/cell got the rated AH of the cells in "run to shutdown" testing of a small UPS. In a 16S configuration, 3.55 volts/cell gives 56.8 volts.
I'd say try 3.25 v/cell and 3.55 v/cell and see which gives more AH. The cells have their rated life (charge/discharge cycles) at 3.65 v/cell so anything less than that may provide some increase in cycle life. I've not seen any test results with charging to less than 3.55 v/cell. If you do both, make notes and share them.
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Post by biggkidd on May 31, 2022 12:33:52 GMT -6
After having this cart for a while and using it as my primary transportation around the property I have no choice but recommend everyone do the same. If you have enough property that you need something to get around in this IS the way to go. First you can carry people and stuff. Second no noise, no gas and minimal maintenance when setup like mine will be. Once the cart and everything is paid for then you pretty much ride without additional expenses. Everything has stuff wear out and or brake from time to time but I'm more talking about fuel and hassle of liquid fueled engines. Plus fuel availability! I was spending about $100 a month getting around the property on an ATV and or garden tractor / lawnmower. In these two months that's over $200 since gas has gone up considerably since the last time I filled our tank. I think Trump was still in office when I last filled the tank! Had I not made the switch we would be needing to buy more fuel now or would have already had to buy more. At this rate we should be good several more months maybe even in to winter.
I've been up and down the hill 4 or 5 times today carrying things half the trips and the cart has used slightly less than 600 watt hours yet the solar panel roof has made almost 1000 watt hours. Having a roof over your head is HUGE in this heat or in inclement weather. The fold down windshield makes it even nicer. Getting in and out is easy too. You can buy them setup or mostly setup like this or save a ton of money and buy old broken down junk cheap and make it the way you want it like I am. If you are a homesteader then you are a DIYer any DIY person can do what I've done / am doing! From my research doing it yourself can save you half or more, even up towards 90% of the cost over buying one new like this.
Another big plus for this over anything else is the fact you can also plug an inverter in and run tools wherever the cart is...
I almost want to shout about this it is a HUGE game changer for us.
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Post by papaof2 on May 31, 2022 16:15:28 GMT -6
As one of the now-defunct high-end car companies (Packard) used to advertise "Ask the man who owns one." Nothing like real world esperience to point to the usefulness (or not) of any tool, device or vehicle.
If you use an inverter, be sure to keep your eye on the AH used so you don't have to walk back. Also be VERY aware of the start current of some common power tools - the bigger chop/miter saws can have a 40 amp (or more) startup surge, which will need a minimum of a 5000 watt (continuous) inverter. I've seen several Youtube vidoes of people "testing" their inverter with a chop or miter saw and them being very unhappy when the inverter either smokes or dies silently. Some inverters have the capability of doing motor starting but you will pay for that. Example: Outback VFXR2812A (12 volts, 2800 watts output, 100 amps charging) has the following specs: Instantaneous Power (100ms) 4800VA (this is what most inverters call "Peak" and it doesn't last long enough to start most motors: fridge, freezer, A/C.) Surge Power (5 sec) 4500VA (this is the motor start power as it is there long enough to get the motor turning) Peak Power (30 min) 3200VA (when you need "just a little more power") Continuous Power Rating (@ 25°C) 2800VA
The "Instantaneous Power" might be good enough that starting that saw won't kill this inverter but Outback wants about $2000 for that inverter. The 2000 watt pure sine wave inverters I have were about $280 each but I had checked the things I planned to power on an inverter and I had a very good idea of the starting watts of the fridge, the freezer and the blower on the gas-fired furnace. The inverter was quite happy running the fridge and the freezer when needed. I've not tried to run the 10" table saw or even a 7 1/4" circular saw on any of the inverters. If I need serious power, there's a 5000 watt gas generator that can run any power tool I have. If you're looking to run power tools, you might want to investigate low frequency inverters.
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Post by biggkidd on May 31, 2022 16:27:24 GMT -6
My Aims 2,000 watt pure sinewave inverter / chargers have pulled everything I've hooked to them including my biggest twin cylinder air compressor which has one heck of a starting load when there's already pressure on the tank. IIRC It has to be on a 20 amp circuit or larger and draws like 13-15 running amps. But they also have a 6,000 watt surge capability for 20 seconds. I bet they also carry closer to 3,000 watts than the 2,000 watts they are rated at.
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Post by papaof2 on May 31, 2022 17:01:57 GMT -6
That 20 second surge capacity is what makes it work. It's there long enough to start a motor. I saw one Chinese "5000 watt" inverter where the "5000 watt" rating was "peak" and it was for 0.1 second - great for advertising BS, but not useful in the real world. That inverter's continuous rating was maybe 500 watts. You have to understand where they put the BS and where to look for the real capacity. It's almost always a case of "The LARGE print giveth and the small print taketh away."
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Post by biggkidd on May 31, 2022 18:56:09 GMT -6
Amen!
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Post by biggkidd on Jun 1, 2022 12:32:15 GMT -6
New battery is finally up to 53 volts. I expect it to start climbing faster soon. I have it on a small 5 amp charger so this is taking FOREVER. I only have two portable 48 volt chargers one is a 18-20 amp fast charger and this is the other one. The fast charger tends to push the voltage up past 60-62 volts. Which is why I'm using this one. I have three other 48 volt capable solar chargers but they are location specific and in use.
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Post by papaof2 on Jun 1, 2022 18:45:14 GMT -6
Because I have a lot of 12 volt batteries, I have two basic 20 amp PWM controllers set up for those "whenever" needs: one for AGM batteries and the other for flooded lead-acid. I can charge a small battery (12AH) slowly with a 20 watt panel and I'm rarely in a hurry to charge any of the smaller batteries - I note the "Date last charged" on a piece of painter's tape and stick it on the battery. If the date is a couple of months stale, I recharge the battery. Easy because the low power stuff has coaxial power connectors (good for a couple of amps) and things can be set up and taken down in minutes - that reminds me: I have a battery on charge and a second one waiting for the charger to be moved. Just a minute or so to connect things and it can stay in place until I get back to it because it can't overcharge.
48 volt devices aren't in the "under $20" category of some of the 12/24 volt controllers I found on banggood.com. Sadly, their stock of that part number only lasted a year or so and I only have two of them :-(
My free bottom-of-the-line group 24 car battery from Craig's List (battery has 2004 date code; I got it in 2006) finally died this year. It's been used for testing fans, lights, car radios (I fixed one for a '60 Chevy for the guy who was restoring that car), inverters, charge controllers, battery chargers, whatever. The now 7-year-old battery I pulled from the truck at age 5 1/2 because the starter was a little slow to my ear recovered nicely with topping off the distilled water in the cells, slow charging and some time with a desulfator. It will replace the "old" battery ;-) I think my grandmother would has blessed that with "Waste not. Want not." ;-)
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Post by biggkidd on Jun 1, 2022 20:14:14 GMT -6
The older folks had a lot of really good sayings that have mostly gotten lost by the wayside. IE: A penny saved is a penny earned. Haste makes waste! and the list goes on.
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Post by biggkidd on Jun 2, 2022 17:58:04 GMT -6
Decided to run a little test on this battery. First a few details Maximum charge is 58.4 volts Dead battery is 40 volts. Man that's a wide spread! From my research I've learned a lot of DIY builders & off griders only charge to 56.8 volts and discharge to 42 volts. Staying in that long life middle span while stretching it much as they can. Those are more like the maximum of both ends and not necessarily the actual working range. The actual working range moves in some on both ends. LifePO4 batteries prefer to be in the 20 to 80 percent range for the longest life from what I understand That's also where most of the useable power is.
Anyway on to my test I only ended up charging the battery to 53 volts that's all my little charger was able to do this time. So I decided to put the 8000 BTU AC on it through a real cheap sinewave inverter. So far it ran one hour and 44 minutes and used 1.134 kWh out of the inverter through a meter. The voltage has only dropped from 53 to 52.2. This battery supposedly has 5.3kWh of storage. I've used a little over 1.1kWh and only dropped .8 of a volt. I am IMPRESSED !
It all fits in a milk crate and one person can move it pretty easy at 70 odd pounds. Rated for or as 51.2 volts nominal and 105 amp hours.
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Post by papaof2 on Jun 2, 2022 18:12:14 GMT -6
16 cell LiFePO4 at 56.8V is 56.8/16 = 3.55V/cell - my favorite LiFePO4 charge voltage ;-) 42 / 16 = 2.625V/cell, just above the recommended 2.5V/cell (2.0 is absolute minimum)
The batteries aren't cheap but they pack a lot of power for their size.
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