Using Accucel-8 as a BMS?

[BrandonB]

BMS: ~$40 for cheapest
Charger: ~$50 for cheapest

Total: $90

Accucel 8: $45

If I'm using an 8s pack (I am), why couldn't I just leave an accucel 8 hooked up to it all the time to balance the batteries and charge them both, instead of buying a low end BMS and charger? The Accucel chargers have a great track record, and I'd be much more inclined to trust them. The only issue I see that might arrise would be the low voltage cutoff. This could probably be fixed inside of the controller.

Thanks,
Brandon

 

[vanilla ice]

I thought about using these chargers as a cell monitor.. Use a small 12v source battery and set it for 0.1 amp balance charge so you could monitor each cell. I think the screen defaults back to the total voltage screen from the 8 individual cell screen after like 10 seconds though?

 

[Drunkskunk]

might work, but not sure how much power it would draw from the battery to stay powered up.

But to what end? If you're running Lipo, ultimatly, you only need something like an LVC. there are alarms for that, or let the controller handle it. Ultimatly, if a cell goes bad, its bad. catching it during the ride won't save it. So checking the balance at recharge is important, but during the ride, its not a real issue.

And if a cell does go bad, a BMS will kill the pack, possably leaving you stranded. Without a BMS, you can make it home. Either way, a cell that would trip a BMS is dead. If it goes out of spec suddenly, it needs to be thrown out. It would likely fail in fire if attempted to recharge.

 

[adrian_sm]

BMS: ~$40 for cheapest
Charger: ~$50 for cheapest

Total: $90

Accucel 8: $45

If I'm using an 8s pack (I am), why couldn't I just leave an accucel 8 hooked up to it all the time to balance the batteries and charge them both, instead of buying a low end BMS and charger? The Accucel chargers have a great track record, and I'd be much more inclined to trust them. The only issue I see that might arrise would be the low voltage cutoff. This could probably be fixed inside of the controller.

Thanks,
Brandon

Do it! I essentially do this for the booster pack on my Giant. But I don't leave it attached all the time, I just plug it in when charging.

The only down sides are:
- no single cell LVC
- having two plugs to plug in when charging

If you are happy with that, go for it.

 

[miuan]

might work, but not sure how much power it would draw from the battery to stay powered up.

But to what end? If you're running Lipo, ultimatly, you only need something like an LVC. there are alarms for that, or let the controller handle it. Ultimatly, if a cell goes bad, its bad. catching it during the ride won't save it. So checking the balance at recharge is important, but during the ride, its not a real issue.

And if a cell does go bad, a BMS will kill the pack, possably leaving you stranded. Without a BMS, you can make it home. Either way, a cell that would trip a BMS is dead. If it goes out of spec suddenly, it needs to be thrown out. It would likely fail in fire if attempted to recharge.

Listen to this guy.
Many run RC chargers to charge/balance single or parallel battery packs of 5/6/8 cells to a certain voltage. It's the best way to keep them balanced. During discharge, however, all you need is a lipo buzzer. An 8S adjustable voltage alarm with LED display can be had on ebay for maybe 5-10 dollars, and the buzzer is fairly loud. It's really all you need. Forget all the mess of carrying an additional battery and a 2lb charger.

http://cgi.ebay.de/1-8S-Lipo-Battery-Tester-Low-Voltage-Buzzer-Alarm-RC-1S-/220740495655?pt=RC_Modellbau&hash=item336528a927

 

[dogman dan]

You don't have to have a bms to ride with lipo. Here's where lipo differs from lifepo4. With lifepo4 you have such a flat discharge curve it's hard without a wattmeter to tell how far down you are. Then at a certain point, WHAM, the battery is dead. A bms is truly usefull then to stop you in time.

With lipo, it's more of a gradual decline in voltage before the dive off the cliff. This makes it much easier to just monitor voltage, using a meter, or a warning buzzer or whatever. You have time to notice it's getting to about that time, and stop before going off the cliff and ruining the battery. At some point, a properly set lvc in the controller will stop you if you blow it. In such a case, it's unlilkely that the entire pack would be ruined. More likely one pack might have an overdicharged cell, and the rest would be fine.

This approach does assume that you do balance the battery often enough, and aren't unknowingly riding around on a severely unbalanced pack.