Max sustained amperage from lead acid batteries

[Daox]

I was talking with Darin today about my battery electric riding mower which I recently got the snowblower attachment working on (pics & video here). He had a concern that I was pulling too many amps continuously. The concern is not for the motor (which doens't heat up at all in the winter), but for the batteries. They are flooded lead acid 150Ah group 31 batteries (4). During normal mowing I probably pull about 80A, so .5C for about a half hour. However, while snowblowing I'm probably pulling much more at times. Darin seemed to remember that with lead acid there is a rule on how long you can pull .5C, 1C, 2C etc. like there is for lithium batteries. I've never heard this, but it made me wonder. He couldn't remember where he read this, so we decided to post here and see if anyone knew anything?

Obviously the peukert effect is magnified quite a bit at higher C rates, but capacity isn't an issue as I just recharged the mower and only put 1kwh (from the wall) into the 7kWh pack.

[Ladogaboy]

As far as I understood it, you can pull as much power as you can pull, and the limitations would come in the form of sag and Peukert's effect. I, too, would be curious if there is more to it than that.

[MPaulHolmes]

It reduces the life on the batteries too. Lee Hart was telling me that deep cycle trolling batteries will last 9-12 months in a car. I don't know what happens to the plates, but the capacity is quickly (several months rather than years) reduced permanently due to the high current draw.

I said, oh ya! Name one example! And he said, "it's all over the EVDL." Then I said, "fine!". haha

[MetroMPG]

He couldn't remember where he read this

Well, the funny thing is I do remember where I read it - EVDL - and who said it - Lee Hart.

I just couldn't find the exact message where he laid out the "rule of thumb" approach to different sustained currents. It was In the Beginning of the ForkenSwift build.

[Daox]

Thanks for confirming Paul. I guess I'll just live with it. I only use it... not that many times a year so cycle life probably won't be an issue, shelf life will be what kills these batteries.

[MetroMPG]

Well, if you have an amp gauge on there, couldn't you adjust the nut behind the wheel to compensate for times where you hit heavier snow? Like gearing down or dipping the clutch?

[Daox]

Eh, unless its a big deal, I probably won't even worry about it. If you watch the video you can kind of see the blower is happy with a certain amount of snow in it. If it gets too much it bogs down, but if it gets too little it doesn't throw as well either.

[Ryland]

Deep cycle batteries often have a 20 hour rating and a 5 hour rating but seldom a rating for a faster discharge then that.
Starting batteries on the other hand are designed for quicker bursts over a shorter amount of time, so I've often wondered if for a high discharge use, like a snow blower, would a starting battery be better?

[rmay635703]

Originally Posted by MPaulHolmes

It reduces the life on the batteries too. Lee Hart was telling me that deep cycle trolling batteries will last 9-12 months in a car.

I don't think this blanket statement is 100% accurate in all circumstances.
Specifically a lead acid battery using a battery discharge tester must be able to maintain a specific voltage during crank, even on a full battery if you can drop its voltage below a certain point even while it is full it is like sulphating the crap out of it locally and it can cause shedding. (aka the reaction can't occur fast enough)

But this is true of any battery regardless of whether its trolling or not.