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Electric EZGO Electric EZ GO Marathon, Medalist, TXT and RXV.



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Old 02-19-2021, 11:34 AM   #1
think7
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Default 93 Marathon - Lithium conversion

Hello - we have an old Marathon we use on the farm. The Marathon gets used 2-3 days a week for 1-3 miles and usually has a small (150 lb total weight if loaded) muck trailer (like a large plastic wheelbarrow) attached and has a big tool tray on the back. Usually only 1 person in it.
The SLAs are going again and I'm reluctant to replace them with same having seen the benefits of lithium and LIFEP04 in smaller applications including a trolling motor I stuck on a kayak.
Cart has 2hp 36V GE motor and 1204 Curtis controller. I've read and watched everything I can on these conversions and vacillate from feeling I could build one using the Leaf modules I see on BatteryHookup - but then I read some more and come across conflicting suggestions on BMS selection and of using contactors and other elecro-mech addons and issues with low voltage cutoffs that if not followed will toast the batts. That scares the heck out of me. I've looked at the drop in kits like those offered by ExtremeTeam who are only a couple hrs away - but which at $1750 for 100AH is probably my last resort. I'd be paying for things I don't need like Bluetooth as I would rather have a simple SOC on the dash or even just an analog dc meter I could wire in. They include built in 12V whereas I'd rather find my own step down for 12V to have a higher amperage for plugging in a tow behind day tank sprayer. And they're backordered anyway. The charger whether sealed or unsealed seems to be a dead ringer for a $100-$200 less expensive one available elsewhere online. I found a smaller drop in for sale at TechDirectClub (they only have one left and it may already be gone) with a 60AH rating that uses Leaf Gen 2 and a claim of 70% batt life but comes with no instructions other than specs. My warped thought process is - even if this only lasts a couple of years at least I'll be able to pull it apart and try and rebuild it and learn something in the process since these Leaf modules appear to be regularly available. TechDirect sell a BMS kit that appears to be the same one as they built the 60AH drop in with (10S although the 60AH drop in says 5S?) and their stuff is put together with a board (instead of busbars) that bolts down over the Leaf batt terminals and has the terminal bank connector for the BMS on the board - so maybe I could build a 2nd one if I need a higher AH or if this one fries. I'm as interested in learning as I go as I am to get an immediate working solution for this Marathon before it craps out.
So my questions are:
1) From the cart description/specs/usage - do you think a 60AH rating would be enough for the 2HP Marathon?
2) Is a 15A 800W charger the correct sizing for a pack rated as follows:
Maximum Current Discharge: 60 A
Maximum Current Charge: 40 A
Storage Temperature: 0 – 89.6 F (-18 – 32 C)
Operating Temperature: 32 – 122 F (0 – 50 C)
Efficiency: >95% DC – DC depending on application.
Fuse Protection: 100 A rated current per string.
Breakers: 60 amps
Design Life: 5+ years
LED DC Meter display the Voltage of each pack.
Nominal voltage 7.5V per module
Maximum charge Voltage 8.3V per module
End of discharge voltage 5.0V per module
Each cell voltage should be less than 4.15V per cell
Each cell voltage should be more that 2.5V per cell
25 ℃, SOC0-100% charging
25 ℃, SOC0-100% discharging
Connectivity: Anderson SB50
3) How do you determine when to charge between uses vs plugging in SLAs after every use and are these chargers typically built to only charge to the optimum voltage vs the max?
4) Any other suggestions to avoid compounding the bad luck in my thinking that often follows me around
Any and all comments would be appreciated.
I can't send PMs but perhaps I can receive them.
Thanks in advance for your time.
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Old 03-10-2021, 08:20 AM   #2
think7
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Default Re: 93 Marathon - Lithium conversion

Well, fortunately no one replied to my questions - which would have egged me on. As a result I came across the post from young Jerald j and his explosion/fire. The pack I got from TechDirect had been damaged in transit (case was all bent up and I had to take it apart and put it in a sheet metal brake just to get it to sit level) but I don't have the skills to evaluate any possible internal damage as a result of the poor Fedex handling and even more inadequate packaging. Sergio's post in commenting on the fire was very instructive: "Hopefully the lesson here is that properly working with lithium batteries without spending money on a commercially engineered turn key solution requires a lot of research and learning the technologies involved."
Sergio confirmed my state of conscious incompetence and I have returned the TechDirect pack and am now searching for a LIFEPO4 drop in solution instead.
So a very sincere thanks to everyone here for ignoring me - it might have saved me from burning down my Carolina barn or worse.
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Old 03-10-2021, 09:11 AM   #3
Bama Brad
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Default Re: 93 Marathon - Lithium conversion

I just saw your post, I too was afraid of making my own so I went with the Roypow. There are other options now, see this post for some comparisions:
https://www.buggiesgonewild.com/showthread.php?t=173142
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Old 03-11-2021, 06:50 AM   #4
think7
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Default Re: 93 Marathon - Lithium conversion

Thanks Brad - I hadn't seen that comparison. I used to import other consumer goods from China so I have some experience in vetting these suppliers - probably going to try and get an off the shelf one customized as a sample - once I started sorting through Alibaba the cream of the suppliers quickly came to the top and some of the current drop in solutions look surprisingly similar so I can sort of guess what brand might come from where. I was closest to choosing ExtremeTeam but didn't like their 12V set up but still might go with them if I can't get a customized one as a sample. Previously opened an account with Allied but in doing further reading on their customer service - they get mixed reviews. Thanks again.
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Old 03-11-2021, 09:05 AM   #5
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Default Re: 93 Marathon - Lithium conversion

I got the Roypow early on and am very happy with it. Of late, lots of people have gone with the Extreme team because of their customer service. I believe you can call and discuss with them what you want/need and the are very helpful. That's something that is not available with the others. Give them a call and see if they can answer your questions/concerns. May be able to modify for you.
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Old 03-12-2021, 07:01 AM   #6
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Default Re: 93 Marathon - Lithium conversion

Thanks - I had spoken with them regarding my 8hp Yamaha with the 700a controller - never heard back. Still weighing options. Will post a new thread with the results of my EZGO install and stats when it finally gets done.
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Old 03-12-2021, 08:27 AM   #7
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Default Re: 93 Marathon - Lithium conversion

Hi Think7. I normally look at the lithium posts in the Extreme DC or EZGO Lithium forums, I didn't see yours earlier because I don't normally go to this forum.

For your questions:
1) 60AH is pretty small, but the AH rating is how far you can go. You have to watch the V rating too. If it says it's 5S that's 5 cells in series. The more cells in series the higher the V. Since these are Leaf cells they are already built internally as 2S. So you are looking at a pack that should be 41V charged to 35V discharged (or thereabouts, assuming these are leaf cells). Given your needs for the cart sound pretty meager, this may well work for you.

2) 15Amps is fine, but you don't need anywhere near that much for charging. For my cart I have a 10 amp power supply. You don't need anything complicated for charging lithium, anything that'll put out voltage will charge. The higher the amps the faster it'll charge, but you could charge it with a 2 amp power supply and more time. You need the BMS to balance it and the charger should stop at whatever max you want to stop it at (redundant safety). I never go above 4.11vpc when charging which gives me 57.6V at the pack (I have a 14S pack). There are some here who go without a BMS, but those guys know what they're doing and accept the risks associated with that. Thermal runaway is no joke.

3) I do not charge my pack after all uses. I tend to charge my pack when I get down to 53V or so. I tell the kids that if the cart hits 48V they need to be in the driveway headed to the garage to park it. I programmed the controller to stop moving at 45.5v. The 'lithium knee' is very real and once you get around 3.20 or so volts per cell (VPC) then you have relatively little capacity left and the V will drop much more quickly. I stop at 3.25 which is a little high. But remember, the less stress you put on the cells the longer they should last. Things that stress the cells are too high a V, too low a V, too high a temp. You can also stress them by too much charge/discharge current but with your setup I don't think that'd be a problem even for a 60ah battery pack. Also too low a temp can be an issue but I live in central FL and that's not a problem I face.

4) Bad Luck. The lithium fire you saw was someone who drained the pack too low. They recovered the pack and it 'seemed' fine and worked fine for a while. But going too low creates dendrites inside the pack which will continue to grow and eventually they can reach the anode (or cathode, I forget if they grow one way) and cause a short. The liquid electrolyte is flammable and a short is a good way to start a fire.

Given all that, the Roy Pow packs and there are several other brands that all will do what you want. If you don't use a premade pack, then you can build your own. Add the BMS (using the BMS to control a solenoid that cuts off pack V when it gets too low/high) and reprogram your controller so it stops the cart when the V gets too low.

If you haven't checked out the All Things Lithium subforum then give it a glance. There are several people buying premade packs with all the safety features built in and people talking about their experience with them.
https://www.buggiesgonewild.com/forumdisplay.php?f=97
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Old 03-15-2021, 04:27 AM   #8
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Default Re: 93 Marathon - Lithium conversion

Thanks bronsonj - that pack has been returned but it did read 40.3 before charging. The charger was rated @ 41V and was adjustable. I'm not sorry I returned it all and will stick with LIFEPO4 leaning towards a pre-engineered solution.

Is the use of the BMS to control a separate solenoid to cut off low/high pack V and the reprogramming of the controller so it stops the cart when V is too low a function of both li-ion and LIFEPO4 modules ?
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Old 03-22-2021, 04:52 PM   #9
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Default Re: 93 Marathon - Lithium conversion

Hi Think7,

Any lithium pack will need to be prevented from going too high/low. I'm not overly familiar with the LIFE cells but I thought they were a bit more forgiving. Not sure though as I have not researched.

The only reason to use the solenoid is because all the BMS modules I have seen cannot handle the drain. So lots of people use the BMS to charge/balance the cells but leave the discharge to go directly from the battery pack. This is simpler to put together but it lacks one of the safety features that the BMS was made for. So that's why people use the BMS to control a solenoid because the solenoid can handle the load. Check out the all-things-lithium sub forum in the Extreme DC forum and one of the members (Sergio I think) did a wiring diagram for the solenoid.
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