How to charge (3) 12v SLA batteries in series

[kmxtornado]

Trying to revive this old guy and hoping you guys can help me out:
https://www.youtube.com/watch?v=dwBNZ0LoXIo

My LiPo battery went bad way back when and I'm replacing the setup with (3) 12v SLA batteries. I know how to connect them in series (do I really need 12AWG wires), but I'm hoping you guys can help me with a wiring diagram on how to charge it.

My controller on the scooter already has anderson power poles so I'll need to use anderson power poles for the 36v battery. It would essentially look like this but with (3) 12volts:

Get ready for the stupid question, "How do I then charge it?"

1. I can't simply build or buy a 36v charger with anderson pole connectors right? I figure anderson power poles aren't rated high enough to take a charge (but that makes me wonder why it's okay to discharge through anderson power poles to power the scooter). Or maybe I'm way off and it's totally okay.

2. If it's not, then perhaps another connector to charge, such as a 3-prong charger port like this? https://www.monsterscooterparts.com/36v-3prong-charger.html

 

[markz]

You need to charge each one to the same level, disconnect each one and charge each one, so you need 3 chargers or take 3x as long with one charger.

Anderson connectors are fine and they come in various ampacities, like PP45 is 45A. You cant really tell just by looking at them, maybe the size of the blade is determined by the ampacity.

 

[john61ct]

All the PowerPole connectors interconnect just fine.

You can routinely parallel 3 SLA for 12V charging but they may not charge quite evenly,

and especially not if approaching EoL.

For restore / cap test cycling do one at a time.

Good quality deep cycling is what you really want, not too pricey, brand new poor quality cheap as dirt.

But best would be 12S LFP, at 6-10x the cost.

 

[999zip999]

Never never fully drain . They hate it. Always leave something in it. Don't let set low charge they like to seat fully charge. Look for new battery for long life and distance. As you may get two-thirds of the capacity out of a lead battery.

 

[kansas]

I disagree that you cannot charge them in series, with a 36V charger. Consider this: A 12V lead-acid battery is already 6 2V cells in series. They are charged as a series unit, not as individual 2V cells. Consider that many trucks and buses have 24V systems, and the 2 12V batteries are charged in series by a 24V alternator. Consider that my first ebike had 3 12V batteries in series, which were not separated or isolated in any way for charging; similarly for golf carts, electric fork lifts, and so on. When the bike's original charger quit, I just used a charger intended for lithium batteries, worked fine. About ten bucks online. The charging curve and final voltage are optimized for lithium, thus slightly different. Lead-acid batteries are not as picky as lithium about how they are charged.

 

[Chalo]

Lead-acid batteries are not as picky as lithium about how they are charged.

But they are much pickier than lithium batteries about only wanting to be discharging, charging, or full. Sitting in a partially discharged state is healthy for a lithium pack, but damaging to a lead pack.

I think it's foolishness bordering on gross wastefulness to use lead batteries for EVs. It doesn't even make sense from a cost standpoint anymore.

 

[markz]

If all 3 generic, cheap motorcycle starter batteries are all the same voltage you sure can charge them in series, but if they are not the same level then they charge to different levels. Do that over and over again without checking, then it can get more out of whack. There is also a chance you charge one battery to high, depending on how out of whack they are, how low one battery is compared to the high voltage battery. Over time maybe one battery can get more internal resistance and reduces voltage more then others, increasing the good battery voltage more. If you dont use a multimeter between each cycle then who knows. Using lead acid batteries for ebikes/scooter is using the battery with frequent charges and discharges causing more instability. You'd have better luck at being balanced if all 3 were bought all at the same time and not having 3 different brands, different ages, different qualities.

For ease of charging, its easier to buy three 12V charging systems and unplug each to charge. You could say its the lead acid battery way of balance charging. Sure you need to unplug which takes a second, rather then getting another device (a dmm) to check voltages and what if your dmm is not found, or needs a 9V battery which you forgot to stock up on, or the fuse blows and you have no clue where to buy a fuse for it after you open it up yet you need to charge the battery asap for a beer run.

With my golf cart up at the cabin, its 48V of high quality batteries which cost $300 each. Easy enough to slap the 48V charger on it and not worry. Not so with cheap, small, generic, motorcycle batteries. Hopefully OP atleast bought them from a local store all at the same time rather then an ebay mystery seller.

I disagree that you cannot charge them in series, with a 36V charger. Consider this: A 12V lead-acid battery is already 6 2V cells in series. They are charged as a series unit, not as individual 2V cells. Consider that many trucks and buses have 24V systems, and the 2 12V batteries are charged in series by a 24V alternator. Consider that my first ebike had 3 12V batteries in series, which were not separated or isolated in any way for charging; similarly for golf carts, electric fork lifts, and so on. When the bike's original charger quit, I just used a charger intended for lithium batteries, worked fine. About ten bucks online. The charging curve and final voltage are optimized for lithium, thus slightly different. Lead-acid batteries are not as picky as lithium about how they are charged.

 

[kmxtornado]

First off, thank you everyone for taking the time to share your input.

Using the setup from my cruizincooler, I used that as a starting point and created this wiring diagram. This allows me to charge using the 3-prong charge port and then power the scooter (and also an e-bike) using the anderson power poles:

I'm pretty stoked that the 3 batteries really do fit inside the case that the scooter came with. Originally, it housed (2) 12v 10ah batteries. By dropping down just 1ah, I was able to fit (3) 12v batteries in here for the overvolt system:

I disagree that you cannot charge them in series, with a 36V charger. Consider this: A 12V lead-acid battery is already 6 2V cells in series. They are charged as a series unit, not as individual 2V cells. Consider that many trucks and buses have 24V systems, and the 2 12V batteries are charged in series by a 24V alternator. Consider that my first ebike had 3 12V batteries in series, which were not separated or isolated in any way for charging; similarly for golf carts, electric fork lifts, and so on. When the bike's original charger quit, I just used a charger intended for lithium batteries, worked fine. About ten bucks online. The charging curve and final voltage are optimized for lithium, thus slightly different. Lead-acid batteries are not as picky as lithium about how they are charged.

Yes, I figured charging in series was the way to go. Makes more sense as far as convenience. Can't imagine taking it all apart every time I need to charge.

Lead-acid batteries are not as picky as lithium about how they are charged.

But they are much pickier than lithium batteries about only wanting to be discharging, charging, or full. Sitting in a partially discharged state is healthy for a lithium pack, but damaging to a lead pack.

I think it's foolishness bordering on gross wastefulness to use lead batteries for EVs. It doesn't even make sense from a cost standpoint anymore.

Each to their own. The scooter came with SLA batteries, so replacing them doesn't do much harm. I once had a LiFePo4 battery that was for an ebike conversion that I doubled for use on this Sharper Image mini electric scooter. Since that died on me, I hadn't touched it since and that was years ago. Reviving now with SLA batteries which are at least half the price of LiPo's. I have too many LiPo's as it is for my other hobbies. Would rather stick with the SLA batteries on this build. But yes, I do recognize the benefits of the LiPo chemistry.

If all 3 generic, cheap motorcycle starter batteries are all the same voltage you sure can charge them in series, but if they are not the same level then they charge to different levels. Do that over and over again without checking, then it can get more out of whack. There is also a chance you charge one battery to high, depending on how out of whack they are, how low one battery is compared to the high voltage battery. Over time maybe one battery can get more internal resistance and reduces voltage more then others, increasing the good battery voltage more. If you dont use a multimeter between each cycle then who knows. Using lead acid batteries for ebikes/scooter is using the battery with frequent charges and discharges causing more instability. You'd have better luck at being balanced if all 3 were bought all at the same time and not having 3 different brands, different ages, different qualities.

For ease of charging, its easier to buy three 12V charging systems and unplug each to charge. You could say its the lead acid battery way of balance charging. Sure you need to unplug which takes a second, rather then getting another device (a dmm) to check voltages and what if your dmm is not found, or needs a 9V battery which you forgot to stock up on, or the fuse blows and you have no clue where to buy a fuse for it after you open it up yet you need to charge the battery asap for a beer run.

With my golf cart up at the cabin, its 48V of high quality batteries which cost $300 each. Easy enough to slap the 48V charger on it and not worry. Not so with cheap, small, generic, motorcycle batteries. Hopefully OP atleast bought them from a local store all at the same time rather then an ebay mystery seller.

I disagree that you cannot charge them in series, with a 36V charger. Consider this: A 12V lead-acid battery is already 6 2V cells in series. They are charged as a series unit, not as individual 2V cells. Consider that many trucks and buses have 24V systems, and the 2 12V batteries are charged in series by a 24V alternator. Consider that my first ebike had 3 12V batteries in series, which were not separated or isolated in any way for charging; similarly for golf carts, electric fork lifts, and so on. When the bike's original charger quit, I just used a charger intended for lithium batteries, worked fine. About ten bucks online. The charging curve and final voltage are optimized for lithium, thus slightly different. Lead-acid batteries are not as picky as lithium about how they are charged.

I may need to charge each battery individually over time every now and then. For regular use though, it makes more sense for me to charge in series. I have a lot of hobbies that involve batteries and making one more than that much more convenient is worth it to me. I don't really have local stores around here to buy this size battery which was important for fitting into the stock battery bag which sits in a tray under the scooter seat. I normally go with Chrome but I couldn't resist the deal on Expert Battery and went with them. Good packaging and fast shipping.

 

[john61ct]

Be very sure all three units are at the same exact resting voltage / SoC when you join the in series.

Consider getting a suitable balancer to keep them that way.

Do not expect to get many cycles before needing to replace. If you are happy with that model batt, the order spares kept full standing by. Shallow discharges will help, get 3-5x the cycles compared to letting them get much below 12V.

But really it would be better to get quality units designed for deep cycling usage, likely AGM, from Northstar, Odyssey or Lifeline.

Less expensive and longer lived would be FLA, from EPM/Deka, Rolls/Surette, Trojan, U.S. Battery, Crown, or Superior.

EPM make good GEL as well.

But LFP would be best.

Nothing to do with LiPo, which would **not** be a good idea.

 

[LeftieBiker]

I had two scooters with series wired SLA batteries. They both charged their batteries in series. One of them, an Oxygen Lepton, was still using the original batteries ten years later when I sold the scooter. They were at about 60% of original capacity. The key to doing it, I think, is to use a high enough (but not way too high) charging voltage, because SLA packs are also not super-sensitive to charging at a somewhat higher voltage. The higher voltage makes sure that the more recalcitrant cells still get fully charged.

 

[Voltron]

Fyi, as mentioned they will go out of balance after a while of series charging, leading to one in the series going high in voltage and cooking itself, and one going low and sulphating.

But you don't need to take it all apart for individual charging. You can just clip a 12v charger onto each of the batteries, while it's still hooked up in series. You can't do that with 3 12v chargers at once as they're not isolated from each other usually, so you have to break up the series, unless you get something like a trolling motor charger, made to do 3 separate 12v at once.

 

[Voltron]

I had two scooters with series wired SLA batteries. They both charged their batteries in series. One of them, an Oxygen Lepton, was still using the original batteries ten years later when I sold the scooter. They were at about 60% of original capacity. The key to doing it, I think, is to use a high enough (but not way too high) charging voltage, because SLA packs are also not super-sensitive to charging at a somewhat higher voltage. The higher voltage makes sure that the more recalcitrant cells still get fully charged.

That's a definite no-no on sealed lead acid. Though less prone to burst into flames, overcharge can pop the vents. High end lead chargers usually have 3 settings for the main lead types, to limit the voltage for the sealed ones but letting flooded ones go to a higher voltage to reverse sulphating, which isn't as big a problem in sealed gel type. Overcooking them is usually the gel killer.

 

[Voltron]

Be very sure all three units are at the same exact resting voltage / SoC when you join the in series.

Consider getting a suitable balancer to keep them that way.

Do not expect to get many cycles before needing to replace. If you are happy with that model batt, the order spares kept full standing by. Shallow discharges will help, get 3-5x the cycles compared to letting them get much below 12V.

But really it would be better to get quality units designed for deep cycling usage, likely AGM, from Northstar, Odyssey or Lifeline.

Less expensive and longer lived would be FLA, from EPM/Deka, Rolls/Surette, Trojan, U.S. Battery, Crown, or Superior.

EPM make good GEL as well.

But LFP would be best.

Nothing to do with LiPo, which would **not** be a good idea.

It's good to have the whole string at the same voltage to start with for capacity reasons, but not like hooking up in parallel, where the electricity tries to rush into the lower voltage battery until they're equalized when connected. In series, a full one can connect right to a dead one and not do anything, with no current rushing around.

 

[LeftieBiker]

(Re: higher charging voltage)

That's a definite no-no on sealed lead acid. Though less prone to burst into flames, overcharge can pop the vents.

I'm talking about bulk charging, not finish charging. I guess I should have noted that. Anyway, this is the most common setup for Chinese and even higher some end scooters: four SLA batteries wired in series and charged in series. It isn't as if this is exotic - quite the opposite.

 

[john61ct]

Yes, cheap and rough, works fine until it doesn't.

The suggestions above are for optimizing within the context of a poor design targeted at low cost and easily available components

 

[LeftieBiker]

Yes, cheap and rough, works fine until it doesn't.

Lithium batteries tend to fail after a few years, too. Expensive and rough. You did see that I got 10 years from 4 AGM batteries wired and charged in series in the Lepton, right...?

 

[john61ct]

Sure, not unusual given usual practice would be replacing at 70-75% SoH 80% for mission critical use cases.

LFP properly cared for at such low C-rates can go 6-8000 cycles likely more, plenty of 15+ y.o. packs still above 90% SoH.

Everything is relative, seeking optimal is very different from "good enough", neither approach is "better" inherently, just a matter if trying to make your choices based on full informatiin.

 

[kmxtornado]

I thought I'd give you guys an update.
Next step was just to connect the batteries in series with my homemade connectors. I'm not usually the guy to make stuff like this albeit it's not the most difficult thing. I snatched some 14gauge wire from an old RC NiCad battery charger that I no longer use and crimped some connectors I got from my local auto parts shop. Tested the voltage to make sure everything was connected correctly. This was actually one of the first times I've used a volt meter. Yeah, I'm an old newb.

This afternoon an idea dawned on me. Rather than wiring it like the diagram above that I uploaded, I figured removing the harness is actually pretty easy. So instead of splicing a charging port and another connector to connect to the scooter, I figured I can just have them completely separate. Use the charging harness when charging and remove it when not in use. Then connect the cables from controller to the battery when I'm operating it and voila!

Took it for the first test spin this afternoon and it worked! I had a hard time getting any Anderson Power poles at decent prices, so I ended up forgoing the turn signals on the scooter and just ran some basic insulated connectors to get the scooter at least operational and it runs now!

I had two scooters with series wired SLA batteries. They both charged their batteries in series. One of them, an Oxygen Lepton, was still using the original batteries ten years later when I sold the scooter. They were at about 60% of original capacity. The key to doing it, I think, is to use a high enough (but not way too high) charging voltage, because SLA packs are also not super-sensitive to charging at a somewhat higher voltage. The higher voltage makes sure that the more recalcitrant cells still get fully charged.

Thanks for chiming in. Can you talk more about your recommendation about "high enough charging voltage"? I've been doing this stuff for awhile but still don't know what I'm really doing half the time. I'm charging the 36v 9ah battery with a 36v 1.8amp charger. How would I increase the charging voltage and to what extent? Are you suggesting using a charger that's over 36v?

Fyi, as mentioned they will go out of balance after a while of series charging, leading to one in the series going high in voltage and cooking itself, and one going low and sulphating.

But you don't need to take it all apart for individual charging. You can just clip a 12v charger onto each of the batteries, while it's still hooked up in series. You can't do that with 3 12v chargers at once as they're not isolated from each other usually, so you have to break up the series, unless you get something like a trolling motor charger, made to do 3 separate 12v at once.
11-16283.jpg

That's a pretty good idea!

It's good to have the whole string at the same voltage to start with for capacity reasons, but not like hooking up in parallel, where the electricity tries to rush into the lower voltage battery until they're equalized when connected. In series, a full one can connect right to a dead one and not do anything, with no current rushing around.

Yes, that was my understanding as well.

 

[LeftieBiker]

Thanks for chiming in. Can you talk more about your recommendation about "high enough charging voltage"? I've been doing this stuff for awhile but still don't know what I'm really doing half the time. I'm charging the 36v 9ah battery with a 36v 1.8amp charger. How would I increase the charging voltage and to what extent? Are you suggesting using a charger that's over 36v?

You want to be charging somewhere in the 42-44 volt range, to get a charged voltage of something like 39 volts, according to the internet. Keep in mind that I've never done 36 volts SLA - only 24 and 48 volts, so I'm not an expert here. Chargers are sometimes labeled by the pack voltage they go with, rather than their actual output voltage, just to make things more confusing...

 

[john61ct]

Just multiply x3 the charging voltage (CV setpoint) that model battery is spec'd for by the mfg.

So if it's 14.6V at the high end of the range, then 43.8 for nominal 36V.

If 9Ah is the capacity, and endAmps spec is 0.005C

then hold the CV setpoint (refrain from dropping to Float V) until charging amps drops to

50mA or so, or at least below 0.1A

This will take longer as the pack wears, so if it gets unreasonable (past say 4hrs) switch to stop-charge at

Current **change** over 1 hour period of less than 0.05A

Stopping before you hit 100% SoC will murder the pack pretty quick

almost as fast as regularly drawing below 50% DoD.

 

[john61ct]

And for current, up to 6A or so would speed things up a little, and if decent AGM may also help longevity