How to monitor a ping battery

[Ham549]

Since I have upgraded my old lashout to a 1,000 watt motor working off a 48v 20ah ping I haven't had any way to monitor the battery condition. Would something like this work? http://www.ebay.com/itm/GOLF-CART-LED-B ... 1c23dcd04f ?

[dogman]

Not well. As we all keep saying, the best way to monitor batteries on EV's is with a voltmeter/wattmeter. The favorite tool for that being the Cyclanalyst invented by Justin at Grin Cycles. But cheaper wattmeter options still work ok.

Particularly with lifepo4, the discharge curve is so flat that you basicly notice the bike is slower, and bam half a mile later you are out. The previous 15-20 miles all felt the same. So a meter like the one you linked to will do about the same thing, it will read full right up to the last mile, then read dead when the battery voltage goes off the cliff just before the bms turns off.

But a wattmeter tells you how many watthours have been sucked from the battery. After some experience, You know that your particular ping battery has the ability to deliver say, 900wh. Now you know exactly where you stand when you look at the wattmeter and see you've used 500wh. You are exactly 50wh past halfway. On the CA, you get a reading of your average wh/mi so far. So if you know you have about 400wh left, and you know the wh/mi, you can now predict very accurately how many miles you can still travel.

Even if you just use a simple voltmeter, with some experience you will get a feel for if my voltage is say 52v, I'm somwhere vaguely in the middle. But if I see 50v resting, now I'm getting into those last 3 miles or so. You can get that warning in time to start really conserving if you must to make it home. Not so great, but still better than finding out you are out with just a half mile worth of juice left.

[Ultraman]

I've bought 5 of these things http://www.ebay.ca/itm/260754656007 to monitor charge and discharge levels on lower voltage batteries. I've also got a few cycle analysts, which gives you much more data and control when riding. But for simple monitoring of amp hours used on batts less than 60 volts (like your Ping), these will work. They also have a balancing function which you won't need, but is handy for lipo.

[dogman]

Lipo has a lot less flat discharge curve than lifepo4. That's why a voltage monitor works much better for lipo, lead, nicads, etc. But even with lipo there is a large part of the discharge where the cells are around 3.85v, and you don't know if you are at the start of the middle, the end of the middle, or the middle.

However, once you know your battery pretty well, a voltmeter and an odometer lets you make a pretty educated guess.

The big problem with pings and other similar bms protected batteries, is that you may think you are charged, but you aren't. A green light on a charger means you are fully charged, or it means the plug on the charger broke. But with a voltmeter, you might go "aha! it's not at 59v, so I'm not fully charged."

Some kind of voltmeter is then the minimum. Once you know you have a full charge, you can just use a speedo to know where you stand on most rides.

[hodgie]

Valuable info - thanks.