Truth in battery labeling

[Oneunder]

Thanks JohnnieB,
That gives me a little to go on. I did get the lithium batteries. They screwed up my order a bit and to compensate me, they said they boosted my Ah. I doubt it but was hoping there was a way of checking. I will try your math and see where it comes out.

[JohnnieB]

Let us know how the lithium batteries work out in your cart.

[Volt_Ampere]

I have used Lipo's in my electric RC models. Great where weight is important but they don't last all that long and they are expensive. One discharge too far and they are junk. They also will catch fire and burn intensely if you ever overcharge them or short them out. Make sure you have the proper charger and make sure your insurance is paid up!

[Oneunder]

Originally Posted by Volt_Ampere

I have used Lipo's in my electric RC models. Great where weight is important but they don't last all that long and they are expensive. One discharge too far and they are junk. They also will catch fire and burn intensely if you ever overcharge them or short them out. Make sure you have the proper charger and make sure your insurance is paid up!

I have also used them extensively with my kid's toys. I think they are fantastic. As long as you have a balance smart charger you will never over charge them. As long as you use low-voltage alarms, you will not discharge them too much. And now they have become cheaper than their NiCd and Nimh counterparts. Those are the Lithium Polymer version which are a tad more unstable than the LiFePO4 that I got.

As it happens, With my batteries, I got both a smart charger and a BMS (battery management system) which prevent overcharging and discharging.

So here are some photos of the switch. Here are the 2 18 volt 120Ah packs with the BMS on top. Each pack weights 15.5 kg



Poor communication between the seller and I led to the soft pack instead of the hard plastic shell. Because of that I put them in a box to ride in.



They are a little hotter than the lead acids with full charge being 39.1 volts. Initially they have quite a bit of zip (just as I remember when the original batteries were new). I am anxious to see how they hold up. I see an upgrade of controller and what not in my future.

[sportcoupe]

Nice work. Looking forward to seeing how they work for run time compared to the flooded lead acid's. The weight savings and deeper discharge capabilities of lithium's are remarkable. I would dump my 72v AGM pack in a minute to run the same in lithium if it wasn't for the cost still.

Did you get your LiFePO4's from Alibaba?

[Oneunder]

I got them from YXM Zone. But I think Alibaba may be the maker. They do alot of business on ebay selling conversion kits for bicycles. I got a little comfort seeing a reliable track record. Not that I have anything to complain about but if I were starting over, I would have spent a little more and bought this.

http://www.batteryspace.com/LiFePO4-...Balancing.aspx

with this
http://www.batteryspace.com/LVD-Low-...P-battery.aspx

It never fails, after you buy something (house, car, etc..), you see something you like a little better.

[yurtle]

That LVD is only rated for 8 amps.

[Oneunder]

Originally Posted by yurtle

That LVD is only rated for 8 amps.

Just like the 36/48 volt to 12 volt reducers run through the key switch with a on/off wire, I think this does the same and just disables the key. Either way, with my voltmeter from Scottyb, I am comfortable monitoring it myself before it goes south of 34 volts.

[Oneunder]

Originally Posted by JohnnieB

Let us know how the lithium batteries work out in your cart.

Here is where things sit.
Since I did not have my digital volt meter when my lead acid batteries were new, my only frame of reference is the number of golf holes I could play before the bar meter began to blink. On new batteries, I could get in 45 holes (not on the same day). This also included the 1 mile round trip to the course.

With my lithium batteries, I discovered after taking them off the charger and sitting for 24 hrs, 40.2 v was the full charge. After driving to and from the course and 18 holes then sitting for 24 hrs, 39.1 v. Then repeat that trip a few days later and 38.1 v. After my third trip, 36.9 v.

I suspect I could continue to repeat this until I discharged them to 33 v. without problem. However, I do not want to tempt fate and have placed them on the charger which is only a 5 amp charger. By the next morning it had shut off.

My only problem thus far is this. If I try to pull a wheelie like Supercoupe, it throws the fuse in the BMS and I have to re-set it. If I gradually depress the accelerator, then no problem. The manufacture says that they set the BMS for a 300 amp threshold and have recommended a 50v 22,000 uf capacitor to be wired in parallel. How this will help is well above my pay grade and I hope JohnnieB may shed some light on this.

My other concern was wire overheating. If you notice the photos, the negative discharge is 3 10 gauge wires and the positive discharge is 4 12 gauge wires. I was worried I would melt the wires. However, after driving up hills etc, I can find no change in temp at all.

[JohnnieB]

Three 10Ga wires in parallel is roughly equal to a single 5Ga wire and four 12Ga is roughly equal to a single 6Ga wire.
If possible, I'd up those to a four 10Ga bundle and a six 12Ga bundle, either of which would approximate a single 4Ga cable.
However, if they are not climbing more than 10°F above ambient temperature, they are handling the load okay.
Just keep an eye on them, especially where they connect to the batteries. That would most likely be the hotspot.

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The capacitor circuit acts somewhat like the water tank on a toilet.
It fills slowly, but when the handle is pushed it dumps a lot of water is a short period of time.

The instantaneous peak current when starting an electric motor is huge, something like 100 times the run current, and while much less, the peak current when accelerating an already turning electric motor is also mighty high.

The max amp rating for a stock PDS controller is 300A, but that is a two minute rating and what the controller clamps the current flow to rather than what the controller actually passes to the motor for the split second before the current limiters kick in. I'm not sure what peak instantaneous current a PDS controller will pass, but it will be several times the two minute rating for a few microseconds, or maybe up to a few milliseconds.

The capacitor will provide a huge amount of amps for a very short period of time, protecting the batteries from being discharged at a destructive rate, or at least that is the theory.

Does the Li battery company provide any wiring instructions for the capacitor?
I'm curious how they fill it slowly and dump it fast. There are a couple ways of doing it, I'm just wondering how they do it.

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When you upgrade your controller, get a programmable one like a DCX. Then you can adjust the throttle up rate to keep from tripping the breaker in the BMS.