Comments about your Lithium Battery

[CP241]

FLA batteries will discharge at amperage ratings significantly higher than lithium batteries.

This isn’t necessarily a limitation to the lithium batteries as they are controlled by a BMS that limits the current. This is done for the safety, and longevity of the pack.

That said, its unlikely your 600A controller pulls anywhere near 600 amps, and under most conditions once your up to speed it’s probably not more than 70 amps or so at the most. The most current draw comes under a heavy load when climbing a big hill, towing, etc. and that is not constant, no more than a few seconds and I’d bet it isn’t more than 400-450 amps for those 2 seconds or so before it starts to drop off…. If it is even that high. It’s impossible to guess without knowing your entire cart setup.

Lithium isn’t for all use cases. Maybe FLA batteries suit you better. But packs can be built/bought to suit pretty much any current demand you could ever throw at them. It’s a matter of how deep you want to dig into your pockets

with the alltrax you do have the ability to plug in and limit that max number and keep it within the specs of your pack. Also with lithium, the voltage doesn’t sag under a heavy load like lead acid. So while the lead batteries may drop to 44-45v under a heavy load, a similarly equipped lithium pack probably won’t drop below 50. The reduction in sag as well as the several hundred pounds of weight loss means you don't “need” to keep your controller maxed out to have the same amount of torque.

So we’ll say with the FLA batteries it’s maxing at 400 amps for 2 seconds and voltage drops to say 45v before the current consumption begins to drop as the cart gains more speed, and the voltage begins to recover. Because the lithium doesn’t sag like that, you would probably not notice any difference maxing out at 200 amps for those couple seconds because of the weight difference and the extra 5 volts available to the pack.


Again this is all theoretical, without knowing exactly what your setup is and having data on how much amperage you’re REALLY drawing and what your sag looks like during those pulls, it’s impossible to say for sure.

[Pat911]

The big difference between lithium and LA when it comes to discharge is that LA will supply as many Amps as its internal resistance will allow. There is no limiting of discharge amps. What you will see though is a very significant voltage drop when drawing high amps, especially as the cells age.

Lithium, on the other hand has a much lower internal resistance (typically 4 to 5 times lower) which will allow it to supply much higher current than LA without the significant voltage drop of LA. So, in theory it’s a no brainer, Lithium will supply much higher currents, at significantly lower voltage drop than LA. This translates to a vastly higher performance increase. Increased internal resistance doesn’t increase with age as much as LA does either.

This is where it gets interesting though. Lithium cannot be allowed to discharge all those amps if you want them to operate safely, and so the BMS is used to limit the output current. As long as the BMS limited current is higher than your cart requires then all is good. If not, the BMS will shut down and you’re going nowhere. LA on the other will just keep going as they have no protection.

The increase in performance when going to lithium comes from two factors, the reduced weight, as Tom wrote above, but also from the much lower internal resistance. When a 16s LiFePO4 battery is supplying 100A, it’s voltage may drop to 50v. That’s 5kW of instantaneous power. When LA is supplying 100A, it’s voltage may drop to under 45v. That’s only 4.5kW of instantaneous power, or a 10% drop. This is especially true as LA ages and it may even be lower than 45v at 100A.

Edit…You beat me to it CP

[CP241]

Originally Posted by Pat911

Edit…You beat me to it CP

It’s not plagiarism if you type what I type in your own words and change it around a bit

Just kidding of course. Slow night at work…….

[Tom47]

Originally Posted by pfleef

Thanks for the quick response. A lot of the lithium packs I see are rated for 100A continuous and 200A for 10 seconds or so. Anyone know the rating for a set of six 8v’s? I feel like it would be significantly higher but can’t find those specs anywhere.

If you take 6- 8 volt Trojan 170 Ah batteries in series, you will have 170 Ah at 48 volts. But remember, only half of that capacity is usable. At 50% they are essentially dead. Not sure about your FLA battery ratings for discharge though.

The Eco Battery 72Ah has a 175 amp maximum continuous discharge. 3 seconds is 600 amps, and 30 seconds is 300 amps. Unless you are steadily climbing hills or off road you will never see anywhere near that.

A hard takeoff with mine will peak around 100 amps and then drop off to 50 at top speed. This is on level pavement. But I have my throttle response set at 40% so I don't get whiplash!

[Tom47]

Originally Posted by Pat911

When a 16s LiFePO4 battery is supplying 100A, it’s voltage may drop to 50v. That’s 5kW of instantaneous power. When LA is supplying 100A, it’s voltage may drop to under 45v. That’s only 4.5kW of instantaneous power, or a 10% drop. This is especially true as LA ages and it may even be lower than 45v at 100A.

Since this is my thread, I reserve the right to select winners in any competitive posts. I have to give the win to Pat for his answer.

But don't worry CP, you were a close second!

[pfleef]

Thank you all for the excellent information, including the referenced article. Very helpful and educational. Sounds like no performance issues so my concern is not really an issue. Love this forum.

[Tom47]

Originally Posted by pfleef

Thank you all for the excellent information, including the referenced article. Very helpful and educational. Sounds like no performance issues so my concern is not really an issue. Love this forum.

You're welcome! If you have any problems at all, just start a thread and you'll get all the help you need.

And please give Eco Battery or Allied Lithium consideration in making your decision. They are both sponsors and you will be well pleased with either one.

And if building your own, there are several knowledgeable members that can help you through it.

[Pat911]

Originally Posted by Tom47

Since this is my thread, I reserve the right to select winners in any competitive posts. I have to give the win to Pat for his answer.

But don't worry CP, you were a close second!

[CP241]

Originally Posted by Pat911

That’s okay. My new cart is lead acid. I charged it when I got it and I’ve driven approximately 35-40 miles since I got it and it is still at 100% state of charge. I’m pretty sure it’s good for another several hundred miles without charging it up again.

[DaveTM]

It's been some time since I installed my new Alltrax SR 48500 controller. It replaced my previous Alltrax...IIRC...600amp controller. (Old controller puked after ten years...not too shabby!!)

In reading through this post....now I'm curious as to what I actually set my max amp draw on my new Alltrax 48500. I'll check that.

I know only of Alltrax (and not other controller manufacture's) but you can hookup a laptop... take your cart for a ride and obtain a second by second spreadsheet file that tells you more information than you want to know.

In my case I took my "hunting cart" (more a need for torque than speed) on a ride with the laptop hooked up. I went up a very steep hill and found out the "max" draw of amps was 345. So, IIRC I set the Alltrax to limit the max amp draw to roughly 300amps.

I took the cart up the same hill and noticed no difference in performance from the motor "asking for" the 345amp, but the controller only allowing 300amps. ....You know...like a kid asking for a quart of ice cream....but you give him\her a "more reasonable" portion.

I'll need to double check what I set the BMS max output to. IIRC I set the BMS max output to be somewhat higher....as a backup....in case the controller get's "wonky" (a very technical term) and doesn't do it's job.

I set the max amp draw in order to provide more available power to get longer ride distance from a full charge.

FWIW