Ryobi 48V LiFePO4 conversion issue_BMS

[werner32]

Below is the specs.

Wired up the battery but would not work. Took off the blade and motor and selfporpelled drive works great.
Issue was BMS would detect a short I think with the blade on so I bypassed the BMS and vola..
Mower now works great.

My issue is now without the BMS bypassed how will I avoid over charging?

Maybe leaving BMS attached to charger all the time until charging is needed...

1X Lifepo4 Battery (48V 10AH)
1X 6A Quick Charger
1X BMS

Specifications：
Voltage: 48 Volts
Lifecycle: >1000 times
Capacity: 10 Amp Hours
Dimension: 195x150x100mm
195x180x80mm
Weight: 7.0KG
Charging Current: 6 Amp
Rated Discharging Amperage: ≤10 Amps
Max Discharging Amperage: 2C

 

[amberwolf]

Sounds like your mower takes more current for motor startup than your BMS can handle. You might leave the BMS hooked up but wire a "startup" switch that bypasses the BMS output FETs until the motor gets up to speed.


However, it's easily possible that as soon as you begin mowing grass it will increase current again beyond what hte BMS can handle, and if that's the case then you need a higher-current-capable battery, presuming hte BMS is is sized already to allow the maximum current the battery itself is capable of dealing with without long-term damage.


When you run it off the original battery, or the new one without the BMS, what is the current draw of the system at startup and while mowing?

 

[999zip999]

Welcome to E.S.

 

[werner32]

Havnt checked the current draw. Bat manufacturer said to just bypass the BMS but ensure I dont overcharge.

Im trying to get the pinouts of the BMS wiring from them as I dont really want to unwrap to get to the cells.

Right now the connector that is not attached in the pic is controlling the startup shutoff. Im hoping that the other connector is for preventing overcharging but like I said until I get a wire diagram from them Im at a loss.

.................
Pic to big..........
http://vpower.hk/product.php?id=113

image of BMS

 

[999zip999]

16a discharge current and 16a charging current ? I wonder if they read the spec. sheet befor posting ? A 16a discharge is probaly the reason for cutoff. I don't think you could charge at 16 amps. Victpower ? Oh.

 

[dnmun]

Havnt checked the current draw. Bat manufacturer said to just bypass the BMS but ensure I dont overcharge.

Im trying to get the pinouts of the BMS wiring from them as I dont really want to unwrap to get to the cells.

Right now the connector that is not attached in the pic is controlling the startup shutoff. Im hoping that the other connector is for preventing overcharging but like I said until I get a wire diagram from them Im at a loss.

.................
Pic to big..........
http://vpower.hk/product.php?id=113

image of BMS

do you understand what they mean by overcharge? you have to make sure that none of the individual cells charge to a voltage higher than 3.9V. do not charge without the BMS until you can measure the voltage. you likely have one cell that is already fully charged and is cutting off the charging mosfet so if you charge without a BMS you will destroy your battery.

 

[amberwolf]

Havnt checked the current draw.

You definitely should do that, because you also don't want to be drawing more current than the cells can handle. If that BMS is a 20A BMS, as it states on the linked product page, then you don't want to be disconnecting it and running the pack without it, if hte pack is a 10Ah 2C MAX pack, becuase 2C is 20A, and means the *maximum* current the pack should ever see, at all. It should only see a maximum of 10A (1C) continuous.

Otherwise, depending on the cells' internal resistance, they may heat up quite a bit and various aging and failure modes begin from there.

If your mower ends up running while mowing at more than 10A, this pack probably isn't really big enough for it, if you want long life from it.

Bat manufacturer said to just bypass the BMS but ensure I dont overcharge.

Only way to ensure you don't overcharge individual cell groups is to sit there with your voltmeter the whole time it is charging and check the voltages on each group, constantly, especially toward end of charge. You *can* just "bulk charge" the pack, which is what they are telling you to do, but then the cells will at some point get out of balance, with some not fully charged and others overcharged, depending on how well matched the cells are (probably not matched at all) and how they change as they age.

Problem with that is you can then over*dis*charge individual cell groups (or the whole battery). I have dealt with repairing Vpower 18650 packs that like other batteries have some weaker cell groups as they age, and without the BMS to cut off discharge when those groups drop to their LVC point, you could damage the groups even more, or worse you could run them into reverse charge, which can result in various forms of dramatic failures.

The BMS is there to help prevent that sort of thing.

 

[werner32]

Im realizing how little I knew about batteries.

I figured there was always more to it which is why I matched the battery with the old NiCad. 48V10Ah NiCad to 48V10Ah LiFePo4 seemed like this would cause me less worry.
The BMS is matched to the battery but Im thinking that the weight and torque of the blade is just enough to trip the BMS to think there is a fault.

I know its not scientific but I had the mower running for 50min and there is no heat of any kind coming from the battery.
Was cool to the touch which surprised me because after doing deck work my drill battery was very warm.

 

[dnmun]

did the cell voltage drop below 2V while under load? 51 minutes at more than 20A for a 10Ah battery, it is not hopeful.

 

[werner32]

Draws 5.89A while connected to the BMS and plugged into the charger. Charger is 6A so it tells me it is drawing straight from that.

With it not plugged in it will not run.

With No BMS it draws over 12A. What do I do now.

All 15 cells 3.2v.