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Old 02-04-2023, 11:18 PM   #1
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Solar charge controller compatibility

I currently have three 50w solar panels with 3 separate 12V charge controllers on top of my 36V golf cart maintaining the usual 6V lead acid batteries. I am currently replacing said (very old) batteries with three 100AH 12V Lithium batteries. The three small 12v charge controllers are not rated for Lithium. What can potentially go wrong if I use them anyway?

Eventually I will replace the three 50w panels and roof with three 100w panels and probably have to buy new charge controllers anyway but thatís not happening for a few months.

We frequently take the golf cart to the beach for long weekends and it just sits in the sun way more than itís actually used so why not take advantage if that.
Edit: I do have a proper 36v lithium compatible charger to charge them otherwise.

Please school me on what I may be missing or not understand.

Link below to current panels and controllers. And below that link to batteries.

SOLPERK 50W/12V Solar Panel Kit,... https://www.amazon.com/dp/B08XYY5CDM...p_mob_ap_share


https://enjoybot.com/products/enjoyb...43474290704599
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Old 02-05-2023, 04:57 AM   #2
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It is simple in my mind. Lithium (and ALL lithium batteries, in fact all batteries, are a little bit different so you need to research your specific brand and model) batteries require a charge profile. In fact all batteries require a charge profile to get the most use out of them. When folks say a charger is not lithium compatible it simple means the charger cannot accommodate the charge profile of the battery.
What is a charge profile? Generally it is how the battery will charge. You'll hear Bulk, Absorb, Float and Equalize thrown around. I won't go into details and try and keep it simple.
A charge profile is charging a battery a certain way for a certain time or event until it is considered "full". My lithium batteries require it to reach 14.2v for 5 minutes. It is then considered full. If the charger cannot be set to notice 14.2v for 5 minutes then, in theory, the charger is not compatible with my batteries.
The charge curve of lithium is much different than lead acid. My batteries will go from 13.8 to 14.2 in a short amount of time (less than 20 minutes in full sun). Also, during this time, one will see the amps go down dramatically. At 13.6v my lithium will take everything I can throw at it. As time passes the voltage goes up and the amps into the batteries goes down fast. At 13.8 it may only take 20 amps, at 14.0 it down to say 10 and at 14.2 it's only a couple of amps. But the 14.2 is important for my batts because that is where cell balancing is occurring. Lithium batts need to be cell balanced regularly. Again, each lithium battery will be different so check with your manufacturer. Lithium batteries do not like to be kept fully charged (float) so the charger should be able to shut itself off from charging for lithium. Lead acid? Completely different charge profile and again depends on the specific manufacturer and model.
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Old 02-05-2023, 07:40 AM   #3
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I’m presuming OP has new LiFePo4 batteries. The answer would be different for Li batteries. Using your old charge controllers will not harm your LiFePo4 batteries as long as you do not exceed the maximum rated input voltage and amperage for the battery. You can charge them even if you’re not using the correct profile. LiFePo4 has a two step profile: Bulk and Absorption. The old charge controllers will stay in bulk mode, and will not be able to “top off” the batteries in high voltage absorption. So you’ll get to maybe 85-90% SOC and charging will stop. If you’re OK with that then you can get new charge controllers later.
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Old 02-05-2023, 08:47 AM   #4
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Solar charge controller compatibility

Yes they are 3 new LiFePO4 batteries connected in series to achieve 36V.

I thought Lithium was Lithium so thanks for the lesson.

As long as under-charging them during day use wonít hurt them Iím good with that for now. I can top them off at night. Their website doesnít have a lot of useful information for me and they donít sell solar charge controllers.

As far as battery life, Is it better if they are discharged more before being charged? Or is battery memory a thing of the past?

I have a pretty steep solar learning curve ahead of me. Eventually wanting to add solar to the rv also.

Here is the LiPO4 compatible 36v charger I bought for charging from shore power.

HTRC 36 Volt Golf cart Charger... https://www.amazon.com/dp/B0B56XV1GY...p_mob_ap_share
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Old 02-05-2023, 09:47 AM   #5
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As long as under-charging them during day use wonít hurt them Iím good with that for now. I can top them off at night. Their website doesnít have a lot of useful information for me and they donít sell solar charge controllers.

As far as battery life, Is it better if they are discharged more before being charged? Or is battery memory a thing of the past?


Under charging Li batteries is OK as long as they get fully charged periodically. Different brands of Li batteries require different time for balancing at the end of the charge cycle. Different battery brands tolerate lack of balancing better.

LiFePO4 batteries do not exhibit "battery memory" issues. Storing the Li batteries at 50% state of charge increases battery life a little. Fully charge including necessary balancing time. Discharge to 50%. Disconnect for optimum storage. See battery manufacturers instructions.

Fully charging after a days use according to battery manufacturers instructions will correct any imbalance the solar controllers leave.

Post make and model of Li battery for better advice.

Here is the LiPO4 compatible 36v charger I bought for charging from shore power.

HTRC 36 Volt Golf cart Charger... https://www.amazon.com/dp/B0B56XV1GY...p_mob_ap_share

The advertising for your three solar chargers and for the new charger both say they are good for Li batteries.

A typical charge profile is 14.4 volts until fully charged.
Hold 14.4 volts for prescribed balancing period.
Drop to holding voltage, sometimes 13.6 volts.
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Old 02-05-2023, 02:32 PM   #6
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Thanks Persistent for giving OP good info.
LiFePo4 manufacturers warrant their batteries for a certain number of charge cycles. Typically the charge cycle warranty is 5,000 cycles, after which the bAttery may lose 20% of its capacity. 5,000 charge cycles is more than most people will use in a lifetime. So there’s no reason for concern about charge/discharge cycling. It’s one of the great advantages of LiFePo4.
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Old 02-05-2023, 02:51 PM   #7
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Solar charge controller compatibility

Thanks for everyoneís advice.

Iím using this golf cart project as a means of learning about solar and current battery technology before adding solar to my DP.

I will have more questions later.
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Old 02-05-2023, 06:15 PM   #8
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Quote:
Originally Posted by Marine359 View Post
Thanks Persistent for giving OP good info.
LiFePo4 manufacturers warrant their batteries for a certain number of charge cycles. Typically the charge cycle warranty is 5,000 cycles, after which the bAttery may lose 20% of its capacity. 5,000 charge cycles is more than most people will use in a lifetime. So thereís no reason for concern about charge/discharge cycling. Itís one of the great advantages of LiFePo4.
There is a lot of good info in this thread I did when I did the install on my motorhome
https://www.irv2.com/forums/f107/16-...de-323250.html
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Old 02-06-2023, 06:23 AM   #9
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As long as under-charging them during day use wonít hurt them Iím good with that for now. I can top them off at night. Their website doesnít have a lot of useful information for me and they donít sell solar charge controllers.



As far as battery life, Is it better if they are discharged more before being charged? Or is battery memory a thing of the past?




Under charging Li batteries is OK as long as they get fully charged periodically. Different brands of Li batteries require different time for balancing at the end of the charge cycle. Different battery brands tolerate lack of balancing better.



LiFePO4 batteries do not exhibit "battery memory" issues. Storing the Li batteries at 50% state of charge increases battery life a little. Fully charge including necessary balancing time. Discharge to 50%. Disconnect for optimum storage. See battery manufacturers instructions.



Fully charging after a days use according to battery manufacturers instructions will correct any imbalance the solar controllers leave.



Post make and model of Li battery for better advice.



Here is the LiPO4 compatible 36v charger I bought for charging from shore power.



HTRC 36 Volt Golf cart Charger... https://www.amazon.com/dp/B0B56XV1GY...p_mob_ap_share



The advertising for your three solar chargers and for the new charger both say they are good for Li batteries.



A typical charge profile is 14.4 volts until fully charged.

Hold 14.4 volts for prescribed balancing period.

Drop to holding voltage, sometimes 13.6 volts.

Running three 12V batteries in series and charging with a single 36V charger, is balancing going to be an issue? And what about pulling 12V off one battery to run low-draw accessories like led lights. What about high-draw accessories like a 12v sound system?
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Old 02-07-2023, 08:10 AM   #10
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Running three 12V batteries in series and charging with a single 36V charger, is balancing going to be an issue? And what about pulling 12V off one battery to run low-draw accessories like led lights. What about high-draw accessories like a 12v sound system?
Using multiple 12 volt batteries in series is always sensitive to balancing. All three batteries must be the identical for optimum life and performance. Ideally they must all be at the same state of charge when they are connected together. Usually that means fully charge each for 14 to 18 hours. Then connect them in series.

If in doubt, connect positives together (parallel). Measure voltage between the three negative posts. Voltage should be zero for each pair. Charge the lowest voltage battery until it is equal to the highest voltage. Measure voltages when batteries are at rest for 3 hours or more.
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Old 02-07-2023, 10:40 AM   #11
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Solar charge controller compatibility

Ok makes sense. Now I need to buy a 12v Lifepo compatible charger.

On top of the batteries it says to charge them individually first time, wait a for them to stabilize, then hook them together in parallel and let them equalize for a certain amount of time before using them connected in series. I would assume that not everyone does this, but could affect longevity.

These have a 10-year warranty and are supposed to be good for 10,000 discharge cycles
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Old 02-08-2023, 05:51 AM   #12
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And what about pulling 12V off one battery to run low-draw accessories like led lights. What about high-draw accessories like a 12v sound system?

Charging in series and discharging individually to get 12 volts is a bad plan. In a series bank, all batteries need to be charged and discharge together so that they stay balanced.

There are other charging configurations, but they are not common. I have a three battery charger that will charge each of three batteries individually regardless of being connected in series, parallel, or independent.

If you need 36 volts for some appliance and 12 volts for others, then use a converter to convert the 36 volts to 12 volts.

If you only need 12 volts, then connect the three batteries in parallel and charge them as a single 12 volt battery.
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Old 02-16-2023, 12:03 PM   #13
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The new LiFePO4 batteries are working great in the golf cart and itís 318# lighter than it was. I upgraded to a Plum Quick motor at the same time. 60% more torque and slightly better top speed.
Probably taking it to Port Aransas weekend after next to give it a real workout. I should be able to keep up with the gas golf carts now.

I bought a step down converter to run 12v accessories, but havenít installed it yet.
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Old 03-05-2023, 11:01 PM   #14
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Ok makes sense. Now I need to buy a 12v Lifepo compatible charger.

On top of the batteries it says to charge them individually first time, wait a for them to stabilize, then hook them together in parallel and let them equalize for a certain amount of time before using them connected in series. I would assume that not everyone does this, but could affect longevity.

These have a 10-year warranty and are supposed to be good for 10,000 discharge cycles
As has been noted, connecting any load to one battery and not the others will cause unbalance that will become a problem and require the original balancing process to be done again in short order.

However, not putting load (small or not so small) on one battery will not guarantee long-term balance among the three batteries. The four series cells in each battery will be kept balanced by the BMS in each battery. But, unbalance between the three batteries can happen (they are effectively three "cells" of a 36V batterey). This unbalance will be slow to develop. Not charging the batteries fully and often will encourage this unbalance. Storage time can also contribute. As the batteries age, this unbalance becomes a bit more likely. I believe that one can buy balance devices for the purpose of keeping three batteries balanced or chargers that will do this. High end 48V commercial systems have this capability. Without such a device, it's wise to check the voltage of each of the three series batteries now and then to be sure they are tracking well and not drifting apart. This measurement is best done as the batteries are being charged and are above 14.0 volts. Since the voltage is rising quickly at this point in the charge cycle, rotate the voltmeter between the three cells quickly and repeat a couple of times.

There are lot of downsides to letting any unbalance develop among series 12V batteries, so it's wise to keep an eye on balance and re-balance if necessary.
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