Ryobi 18V pack repair

[atatistcheff]

I'm looking for some thoughts or experience on lithium power tool battery packs. I've been repairing some of the Ryobi 18V packs which are dead or just below the BMS charge voltage. It's pretty easy and normally just involves opening the pack and injecting some volts to get the pack up to a point that the regular charger will work. Of course, sometimes there are dead cells in the pack which can be replaced to make it usable again.

I'm finding quite a bit of variation however between the watt hours available in various packs. What I'm seeing is that when I replace all the cells (5) in a pack with known, tested values the total watt hours does not add up to what it should be. For example, 5 cells tested at 1100 mAh should provide about 84% of the rated value (new cells are 1300 mAh). However, this 1100mAh pack is coming in at about 60% of the rated value instead. I suspect this is due to the cells being out of balance. One cell gets low and the BMS cuts off the pack before the other 4 have discharged fully.

I think my mistake was not to ensure the cells were all perfectly matched - at least in their voltage - before putting them in the pack. This brings me to my question. Does anyone know if these power tool pack BMS boards actually do any cell balancing? The BMS looks pretty complex so I would assume there is some balancing going on. It seems that the pack capacity would prematurely degrade over time as the balance drifts. However, if they do balance then my oversight of not matching the voltages well should eventually be corrected.

I can't seem to find any information on how the Ryobi BMS works (not that this surprises me). Does anyone have any knowledge or experience with these BMS boards?

 

[DENWA]

Yes. They are lowest price from a company called TTI. They were VERY bad design a few years ago. NO balancing at all. Usually pulling power for the safety circuit off the lowest cell stack causing an imbalance!

I used to repair them with new 18650's but they started selling 2 big packs for $79 at Home Depot so its just not worth it to me.

I did balance my cells before putting them in but to be honest the circuit is such junk they would go bad in 2-3 years no matter how much you use them. Which is how I believe they designed it

 

[SolarRat]

Those batteries are junk. I have a few that constantly fall below the charger threshold. I drilled little holes in the sides of the battery pack near where the main + and - terminals of the cells are so I can give them a boost charge to get them above the charger cutoff without disassembling the battery every time.

I'd like to replace the cells with high quality 3000mah high drain cells...just haven't gotten around to it yet.

My "2 amp" and "4amp" packs are 5s and 2p5s. With their 1300mah cells, the math doesn't add up. They are really 1.3a and 2.6a packs. The 3000mah cells should more than double their runtime.

 

[Deveak]

Sorry to revive a dead thread but does anyone make a good full featured 5s bms?

I have some old Ryobi cells and batteries but honestly I just want to build a custom pack and escape from the low quality batteries they sell. Want something bigger, maybe a backpack and use an old single stack battery as an adapter.

 

[Maintenance guy]

Batteryhookup

Brand name power tool BMS

This is what I do also, I get good quality new packs breaking them down for the cells and order good BMS's. Customers always happy with higher capacity batteries that actually last many years. I even made a backpack 20 volt for a guy at 30 ah. I used the battery shell and connector with a noodle soft 10awg silicon wires to the battery pack. When he takes it off the tool he sticks it to velcro on his arm out of the way.

I hope this helps!

 

[Deveak]

Batteryhookup

Brand name power tool BMS

This is what I do also, I get good quality new packs breaking them down for the cells and order good BMS's. Customers always happy with higher capacity batteries that actually last many years. I even made a backpack 20 volt for a guy at 30 ah. I used the battery shell and connector with a noodle soft 10awg silicon wires to the battery pack. When he takes it off the tool he sticks it to velcro on his arm out of the way.

I hope this helps!

It does. I bought a 3d printed tool adapter for ryobi tools. I mostly bought it because I can pop the bottom of it off and directly wire a custom pack to the tool. The plan is an LTO or lifepo4 pack. LTO would be awesome. Probably use XT connectors, like XT 120 so I can swap out adapters and tool heads for a variety of 20 volt tools.

Lifepo4 definitely crosses the voltage threshold if you charge to 3.5 and run 6S.
LTO I think 7S or Maybe 8S and not fully charge it. The minimum voltage would be a lot lower. I think its 14 volts for 5S NMC and a max of 21 volts. Most tools I would be using would be simple brushed tools. I don't think voltage is a huge deal to them if its off by a volt or two. HP+ tools and brushless motor controllers may have a shorter ceiling. A single stack of 7S-8s LTO cells at 20 AH would run me $126-144 at battery hook up, so the same as a larger cheap ryobi battery with a fraction of the cost.
LTO BMS might be hard to find in that configuration. I think a simple LVD cut off and HVD cut off might be the way to go and using super cap balance boards to keep them balanced. 3C is max I would ever put on these. I doubt I would get even close to that.
Over temp shouldn't be much of an issue or under temp. At worst I can wire up a simple digital temp gauge on the tool adapter to monitor it myself.

 

[BuffaloTrace]

It does. I bought a 3d printed tool adapter for ryobi tools. I mostly bought it because I can pop the bottom of it off and directly wire a custom pack to the tool. The plan is an LTO or lifepo4 pack. LTO would be awesome. Probably use XT connectors, like XT 120 so I can swap out adapters and tool heads for a variety of 20 volt tools.

Lifepo4 definitely crosses the voltage threshold if you charge to 3.5 and run 6S.
LTO I think 7S or Maybe 8S and not fully charge it. The minimum voltage would be a lot lower. I think its 14 volts for 5S NMC and a max of 21 volts. Most tools I would be using would be simple brushed tools. I don't think voltage is a huge deal to them if its off by a volt or two. HP+ tools and brushless motor controllers may have a shorter ceiling. A single stack of 7S-8s LTO cells at 20 AH would run me $126-144 at battery hook up, so the same as a larger cheap ryobi battery with a fraction of the cost.
LTO BMS might be hard to find in that configuration. I think a simple LVD cut off and HVD cut off might be the way to go and using super cap balance boards to keep them balanced. 3C is max I would ever put on these. I doubt I would get even close to that.
Over temp shouldn't be much of an issue or under temp. At worst I can wire up a simple digital temp gauge on the tool adapter to monitor it myself.

You don't absolutely have to use a BMS for LTO. I know a lot of car audio people use them as starter batteries and audio system with only a simple balancer. Those LTO can take abuse.

 

[Deveak]

You don't absolutely have to use a BMS for LTO. I know a lot of car audio people use them as starter batteries and audio system with only a simple balancer. Those LTO can take abuse.

I would at least want a low cut off. It’s likely at one point I would drain the cells and if not to protect the cells, protect certain tools. I need to have a gander at the brushless tools. The only stick in the mud I think I will run into is some tools may have communication wires. I know Milwaukee does, but that’s 12 volts.

 

[orangezero]

I've used LTO pouch cells in relatively low power applications with no bms at all. If you avoid a bms for whatever reason, I think it would be nice to have a small screen that displays the voltage of each cell in series so you could self-monitor. At the very least a single total voltage display... The supplier I bought them from was friendly and talked about them a lot when I picked them up. He said he dropped the voltage to almost zero and they later still worked. And he said he charged a few up to 5v (on a 2.3v cell) and they later still worked and continue to function. I don't go that crazy, but it also helped me decide to try it without a (at the time expensive) bms first and just self monitor.

I have two of these 18v ryobi packs and after 8-10yrs one of them finally died. I may try to open up and see the voltages before I give up.