6VDC Battery Charge Question: Constant Amps Phase

[gathermewool]

I didn't remember a lot of what I'd previously learned about charging LA batteries -- ever since getting a "smart" charger -- so I had to refresh my memory (e.g., from Battery University, etc.). I still unclear on a few things.

INFO:
1. Battery: 6VDC, sealed lead-acid (SLA); I believe these are typically 8Ah or around there
2. PS: Penovo 30VDC/5A
-----can be currenty (voltage) controlling (i.e., maintain constant, set current (voltage))
3. Voltage Chosen: 2.35VDC/cell = 7.05VDC charge voltage
-----Seems like a good voltage for a small SLA battery
-----0.337A: corresponding current, with the PS hooked up, controlled to 7.09VDC (close enough to 7.05VDC)
4. Current Limit: 1/10C
-----I'm not sure how to control current for the first phase of charging
-----8Ah * 0.10 = 0.8A (800mA) seems way too high for such a small battery
-----I definitely wanted to check in with you guys before raising > 0.337A (337mA)

PS Setting (Pending BITOG Review):
Current-Control-Mode: Set to 0.337A
-----This corresponds with an intial voltage of 7.05VDC (2.35VDC/cell)

Battery University:
Battery University lists suggested limits while charging using a PS, but doesn't mention whether to control by amperage or voltage, though this may be implied in how the charging phases work (i.e., phase 1 is constant current).

Question:
So, how do I set my initial current for phase 1?
What is the ideal way to charge in each phase, using a PS?

 

[gathermewool]

Here's some data, from commencement of charging:

Constant Current Setting (intial): 0.337A
1346: 7.09V (0.337A)
-----I accidentally blipped the A up to 0.339A
1406: 7.11V (0.339A)
1430: 7.15V (0.339A)
1433: 7.17V (0.339A)

 

[gathermewool]

Ok, so here's my plan (just in case I don't get responses until much later):

Phase 1:
1. PS (constant-current-mode): maintain between 2.35 and 2.40VDC/cell
-----Adjust current to do this
2. Phase 1 complete when voltage stops rising at whatever constant current (peak voltage for set current)

Phase 2:
1. PS (constant-voltage-mode): set for 7.05VDC (2.35VDC/cell)
2. Battery is full when current stops lowering at 7.05VDC (2.35VDC/cell)
-----BU seems to indicate that full is also ~3-5% of Ah rating
-----I don't know what the capacity is - the battery has been sitting for a while

Data:
1345: Constant Current Setting (intial): 0.337A
1346: 7.09V (0.337A)
1406: 7.11V (0.339A)
1430: 7.15V (0.339A)
1433: 7.17V (0.339A)
1500: 7.27V (0.338A)
1508: Constant Current Adjusted to 0.175A
1510: 7.05V (0.175A)
1523: 7.08V (0.175A)

 

[EdwardC]

I think you got it right for the most part. Typically from a PS, you have the option of CC or CV. The supply obviously has to output a higher voltage than the battery voltage for the current to flow the right way. In CC mode, the supply constantly adjusts the output voltage however necessary to maintain the current. In this CC phase, you should stop when the battery voltage hits your target (7.05V to 7.2V in your case). Once you disconnect the supply at the point, the battery voltage will drop.

In CV mode, the voltage is fixed and the current changes based on the load. In this stage, you set voltage you want it to reach (7.05V), and the supply will maintain that voltage. Since that voltage is higher than the battery, current will flow into the battery. As the battery continues to charge up, the battery voltage will rise, and at the same time, the current will taper down.

 

[gathermewool]

Thanks, EdwardC. Kid just got done playing with "Power Wheels" for the first time since we moved last year - lasted way longer than I thought. It helped that I resorted to letting him ride down our gradual driveway and then carried the car back up to the top after seeing how much this poor little thing struggles on the up-hill!

Phase 1: Anyway, I'm trying something different this time. I'm going to assume a Ah rating of 6Ah and start off with 0.6A (600mA) until my target voltage of 7.05 to 7.15VDC is achieved - I'm giving myself a wide margin, so I don't have to watch it like a hawk, like I did this morning. I've also got a webcam trained on it, so I can see the PS whenever I want.

-----I'll keep an eye on battery temperature, since I'm almost doubling the current, though it stayed at ambient this morning, so I'm not too worried.

Phase 2: Once I reach my target voltage, I'll switch to voltage-control-mode and maintain ~7.05VDC until current stops lowering.

Much simpler than what all I did this morning! I'll try to plot out how this curve looks, so I can compare it to what's shown on the Battery University site.

 

[pandus13]

Originally Posted By: gathermewool
...Kid just got done playing with "Power Wheels" ...

[off-topic]
if one searched the web, would find a lot of info on Power Wheels 12/24V conversions (and rewires) and even a Yamaha motorcycle engine conversion....
[/off-topic]

 

[gathermewool]

I didn't stay up to get enough data to show a good curve. This is the second charge, from 6.23VDC resting voltage (The Constant Current to Constant Voltage switch was at 2141):





Originally Posted By: pandus13
Originally Posted By: gathermewool
...Kid just got done playing with "Power Wheels" ...

[off-topic]
if one searched the web, would find a lot of info on Power Wheels 12/24V conversions (and rewires) and even a Yamaha motorcycle engine conversion....
[/off-topic]


He got a power wheels and I got a 1/10 scale RC truck. I planned on upgrading both, but [I never got around to it].

I've been thinking the same thing. I spent some time on the modifiedpowerwheels and rcuniverse forums, but haven't done much with the information.

Powerwheels: I'm thinking it's too cheap to mod. The front suspension is already very weak-looking and bound to break eventually. It's also 1WD, with cheap plastic gears that will likely break with any more power/strain placed on it. That's not even to mention how the motor might take to a 12V battery!

The wheels have only a single strip of grippy rubber tread down the center-line of the plastic tires. After maybe 3 total hours of use on concrete (and about the same on smooth surfaces), this rubber section has almost completely worn away.

RC Truck: I got a Ruckus 2WD 1/10 scale truck for cheap from a local guy who hadn't used it a year or more, IIRC. The Ni-MH battery that came with it was dead (the truck would turn on and I could almost get the steering to try to turn, but the wheels wouldn't rotate); however, there was hope in that the voltage didn't indicate that it was definitely dead-dead (like when you check a rechargeable Ni-MH AA battery and find it with < 1.0VDC!) It took a charge and surprisingly gave what I expected as normal run time and still works!

I bought a slightly higher voltage and capacity Ni-MH battery, but that's it. The brushed DC motor gets hotter with the higher voltage battery, but I'm not concerned. If it dies, replacements are cheap and it'll give me a [not very good] excuse to upgrade to brushless...maybe. I checked the suspension fluid (which was still full and clear) and other components, and they're all good to go. Apparently, the receiver is pretty OK, but the rest of the components are just meh. For the price, I think I read a consensus that it was a pretty good bang-for-the-buck, beginner truck, which is consistent with what I've experienced.