10-28-2018, 11:04 AM | #11 |
Gone Wild
Join Date: Jan 2013
Location: Saint Petersburg, FL
Posts: 2,089
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Re: DIY Lithium Conversion
Thanks Johnie B! Yurtle schooled me on the same instruction.
Yurtle, the turbo option is interesting, except initially I was keeping the stock controller and running it at 57.6V to 58.8V. If I add just one more cell that'd be 61.5v to 63V which I don't think the stock controller would handle. I know the stock controller can handle 60.2v... This leads me to BONEHEADED MOVE #2... I was using the stock charger to charge the pack. The stock 13 amp charger would raise the V about 0.7 to 0.8v for every 10 minutes on the charger. So I'd set the timer and go out and unplug it. This worked fine, until I forgot to set the timer.... I bought a charger that was correct, except it was junk. It charged the pack one and a half times then all the magic smoke went out of the charger. I planned on adding a timer to the outlet but never got around to it. So I charged the pack all night with the stock charger. In the morning it was sitting at 60.2v or 4.3vpc! Immediately I went for a ride with one foot on GO and one foot on the brakes to drain off some V. Good news is nothing caught fire. Bad news is over charging dramatically stresses the cells and ages them. |
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10-28-2018, 11:39 AM | #12 |
Happy Carting
Join Date: Dec 2007
Location: Southern California
Posts: 73,406
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Re: DIY Lithium Conversion
Lithium is not forgiving. The reason everybody can use and maintain a golf cart is in part due to the very forgiving nature of lead acid batteries.
The lithium chemistry is very different animal. Remember all the Samsung phones that caught fire while charging? Lithium. Plus like you said they damage easily. One incident can greatly diminish the health of a lithium cell where a wet cell battery can take a lot of abuse comparatively. Anybody reading this should recognize the importance of a proper charging system not only for battery life but safety. |
10-28-2018, 04:21 PM | #13 |
Over This Interview Is...
Join Date: Jun 2012
Location: AZ
Posts: 17,449
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Re: DIY Lithium Conversion
These are the reasons I think it's insane to do lithium without a BMS. I don't trust "bottom balance method" alone either. If not for safety reasons, just to protect your investment.
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10-28-2018, 06:11 PM | #14 |
Gone Wild
Join Date: Oct 2012
Location: Southwestern Pa.
Posts: 6,214
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Re: DIY Lithium Conversion
I agree with CGtech.....to do this IMHO, without a quality BMS, and a proper LITHIUM battery charger just seems to me to be asking for trouble.
If your spending $450 to $500 for batteries, and in some installs up to and over $1,000....why would you not want a BMS that will shut down your charging when it goes above the limit, and the same BMS shuts down your cart when the lower charge limit is reached? In addition, the BMS will keep the individual cells in balance so that you don't have the chance of one given cell being charged well over it's limit....and bad things could happen. The benefits of a lithium pack will be (and I'll be the first to post the truths or not) less maintenance (no cleaning terminals every 60 to 90 days....no water levels to monitor....a weight savings of 400-lbs....longer run distances.......and no power loss on inclines). The maintenance of the lithium will revolve around reading the BMS monitor, and understanding the information it's telling you. A lithium user should have a basic knowledge of their set up. And the user should keep in mind that overcharging is very bad....and drawing the volts under published minimums is also very bad. |
10-28-2018, 06:23 PM | #15 | |
Gone Wild
Join Date: Dec 2011
Location: Central Coast Cali
Posts: 161
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Re: DIY Lithium Conversion
Quote:
Good information Dave |
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10-28-2018, 06:39 PM | #16 |
Getting Wild
Join Date: Sep 2018
Posts: 96
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Re: DIY Lithium Conversion
I would like to add the importance of securing them properly in the battery compartment in case of an accident. If for some reason they are damaged in an accident a serious fire can result. I've seen a couple of lithium battery fires and it's something to behold. There will be nothing left to salvage and will pretty much be stand back and let it burn hoping nothing else important is nearby. In cars, the battery area is seriously fortified for this reason.
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10-28-2018, 07:00 PM | #17 | |
Just Gone
Join Date: Sep 2015
Location: North Carolina
Posts: 3,549
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Re: DIY Lithium Conversion
Quote:
I couldn't find any information where someone had done it this way and I didn't want to be a guinea pig and be out a lot of $$$ if it didn't work. |
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10-28-2018, 07:24 PM | #18 |
Gone Wild
Join Date: Sep 2012
Location: Charlotte, NC
Posts: 9,329
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Re: DIY Lithium Conversion
A couple of notes on using a single pack with separate taps for power:
1) You still need 2 chargers as the amount of energy removed from each section is so different that there is no practical BMS arrangement that can shunt enough current for a single charger to charge the entire pack. 2) You need to be careful in keeping the two negatives always isolated from each other (Accessories and Controller). All accessories negative have to reference the 12v negative and if any relays are wired to the key switch or reverse buzzer, they need to reference the Controller B- negative. |
10-28-2018, 08:54 PM | #19 | |
Gone Wild
Join Date: Oct 2014
Posts: 353
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Re: DIY Lithium Conversion
Quote:
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10-28-2018, 09:42 PM | #20 | |
Gone Wild
Join Date: Jan 2013
Location: Saint Petersburg, FL
Posts: 2,089
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Re: DIY Lithium Conversion
Quote:
As for the new charger, the difficulty I found was there are many chargers for a 12S pack and it seems the next common pack size was 16S... So my 14S was just out of luck and I certainly wasn't going to buy another lithium charger like the first that was good for only 1.5 charges... I found Meanwell sells a charger with algorithms built in for Gel, AGM, FLA and lithium that is exactly what my 14S needs. Lithium really just needs something to provide current and will cut off where you need. I connected the charger set to Gel (which has the lowest voltage) and watched the pack like a hawk while charging. When all was said and done it stopped at 56.6v. This is lower than I want but still plenty fine. I haven't yet tried the AGM setting but that should get me in the mid 57v range which is where I want to be. This charger took several hours to charge the pack, but charging slowly is not a problem with lithium. With lithium anything that causes heat is a problem, charging quickly builds heat, slowly does not. As for charging, at the moment I am using a Top Balance method. I have the boards for this but have not installed them. The biggest reason is that I found out that when the board fails, it fails in a way that causes a continuous parasitic draw... So I check my cells about once per week, maybe less. Takes 30 seconds to see every cell is within 0.01V of each other then I go on my way. My cells started out this close and have not strayed yet. I've been running my pack for about 4 months now (or more). I do plan on installing the BMS with balance boards, but I want to do so with a quick disconnect type of connection and haven't figured out how I want to do that yet. Other people use the Bottom Balance method and I think that is probably a better method and may switch in the future. Also of note, under normal circumstances, my plan is to not take my pack below 45.5v or 3.25vpc and not go above 57.4v or 4.1vpc. These cells are good for 3vpc to 4.2vpc and some people even take them down lower, but with lithium the cells will have a 'knee' in the discharge. So it is a very linear discharge until you get close to their limit, then one or more cell in the pack will take a dramatic downturn in the voltage of that cell. If you are not monitoring each cell very carefully then you will need to give yourself a wide margin of error. Lithium will live a long and happy life if: 1) don't over charge them 2) don't draw them too low 3) don't leave them fully charged for long periods of time in very warm environments 4) don't get them hot |
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