using my multimeter?

[randomlight]

I just bought a sperry dm6400 multimeter to be able to check the percentage of my batterys charge but I don`t know how to use it.
Sorry for the lame question but could someone tell me what setting I should use thanks.ps I have included a link to a photo of the multimeter below..... any help would be appreciated http://www.clanteamxtreme.com/forums/cTx_Reviews/Reviews/tr2rx750/4.jpg

 

[Drunkskunk]

there is no measuremnt for percentage of charge, unfortunatly.

there are ways to get a general idea. If you know what the voltage is when the battery is full, and what type of battery chemestry it is, then you can get a good estimate from measuring it's voltage.

What type of battery do you have?

 

[randomlight]

My battery is a li-mn 36 v 10-13ah .. I was under the impression that one could see what percentage of charge was in the battery because when I bought the battery (used with bike) I took it to the dealer who told me the battery was probably good because it had a 50% charge in it according to his multimeter reading. I am a bit more confused now .
.

 

[bionx 1954]

A 36v limn battery FULLY charged would be about 41-42 VOLTS right after being charged, and around 30 Volts when it is almost fully drained, so lets say it measures 36Volts that means that the battery is about 50% charged so about 1/2 of the capacity of the battery is left

 

[dogman dan]

Like he says, you can measure it, but it's only an estimate.

You have to find out what the scale is by measuring your own pack, since it will vary some from others. I don't have the numbers for li mn, but you can get them here if somebody chimes in, or look them up someplace. Your packs fully charged voltage will be what it is, depending on what your charger does. So charge up and measure that. That's your 100% charged number. Then find out what the voltage per cell should be at 100% discharged. Multiply by the number of cells in your pack. 12 I think? Or is it 10 for limn? Anyway, that's your never go below number. Once you do some riding, checking the voltage periodically, you will eventually get a feel for what is half, what is 3/4 etc. Ideally you'd never discharge below 80% unless you must.

One thing to remember, is that with all lithium, the voltage drop is a lot flatter than with other chemistries like nicad or lead acid. So the amount the voltage drops in the first 50% of the discharge may be very small, while at some point near the end, voltage will drop like it went off a cliff. Again, the best use is to never get near that cliff, let alone actually take your cells off it.

So it can be pretty hard to precisely measure % discharge on lithium by measuring voltage. It really is a bit of a guesstimate. That's why the dealer said probobally good, instead of definitely good.

 

[ebent]

The best answer is to get a cycle analyst. http://www.ebikes.ca/drainbrain.shtml It is the gold standard of keeping track of your battery. I was stuburn and thought I had a cheaper way. I paid for a dumb thing first, then I gor the real thing. I'm sure that in regard to this intelligent source of Endless Sphere, almost all would agree that a cycle analyst is by far the best choice. Good luck.

 

[Uncle Ron]

My battery is a li-mn 36 v 10-13ah .. I was under the impression that one could see what percentage of charge was in the battery because when I bought the battery (used with bike) I took it to the dealer who told me the battery was probably good because it had a 50% charge in it according to his multimeter reading. I am a bit more confused now .
.

randomlight,

Drunkskunk is right, at least as far as my limited knowledge goes. You can measure the voltage of your battery in various states of charge and discharge with a multimeter and get a rough idea of the state of charge of the battery. Coupling that with your experience from measuring different distances traveled at different charge states you can make a rough percentage estimate of what your battery is capable of in terms of distance traveled according to what you read with your multi-meter. Bear in mind that you need to be precise about how and when you measure your battery voltage as the readings will be different depending on whether the charger is connected or not and will drop significantly when the motor puts the battery under load. Also bear in mind that your battery loves having a full charge, so don't be cavalier about charging it and do so whenever you can. A volt-meter can keep you appraised to the state of your battery and when used periodically will give you an indication of when the battery capacity is starting to slough off. Only an onboard, watts-up or cycle analyst meter which measure voltages and amperage uses under load, over time can give fairly precise info about what to expect from you battery and help you to use it wisely for speed and distance.

Had you given the battery a full charge before taking it to the dealer, or did you ride there and how far? The dealer was probably questimating at a percentage from his/her experience and it couldn't have been very accurate. If you did not charge the battery before taking the bike there or riding it there, any estimate by the dealer wouldn't be much above garbage. Not enough info here. I have no way of guessing at the state of your battery from what you've told us. Perhaps the dealer did.

As far as actually using the multi-meter goes, I'll try to help, but take it with a grain of salt because I can't read the text on the meter from the picture. The black, negative lead plugs into a com port, short for common. The red, positive lead plugs into a a port that is probably labled voltage, for both DC, direct current, which is what you are measuring, and AC, alternating current, which is what powers your household. The big dial on the front , you turn to DC voltage. There will probably be more than one setting labeled DC-V in various ranges. Find the one whos range corresponds to the around the 36v that you will be reading. The multi-meters settings are now correct and you can turn on the power and hold the negative probe to the negative battery terminal and the positive probe to the positive terminal. Hold them there until the multi-meter calibrates itself to 0 and then gives you a reading (1-3 seconds.)

A fully charged, working lithium battery will have a reading in the roughly 42 or 43 volt range, which cooresponds to when the smart charger is programmed to stop pushing amps to the battery against its charge resistence. This fully charged voltage will drop slowly over time and others can give you an idea of when you need to start being concerned about your battery life. Remember, you are measuring no-load voltage here. The controller on your bike will cut off the battery and motor and leave you under leg power alone when the voltage falls into the 30-31 volt range so as not to damage the battery. It's best to not take it that far on a regular basis and your battery will have a lot more cycles than it is rated for. When you measure the cut off battery with your muli-meter it's liable to measure in the 33-35 volt range. Nothing is wrong, because you are seeing the difference between load and no load measurements.

Take lots of voltage measurements under varying conditions of charge, discharge, type and distance of travel, and before long you'll be able to make reasonably accurate percentage questimates yourself.

 

[oldpiper]

One word of caution, if you touch those probes together while they are connected to the battery outputs, you will melt them (the metal, not just the plastic) with an exciting flash and create a pretty good char. Even if it seems like it is impossible to do, somehow it becomes very easy when you are thinking about your next step. Trust me on this one. That's why I took an extra set of probes (OK, a melted-tips pair) and soldered a plug to match the one on my battery charger wires. Now it's NOT going to happen again (until I can't find it and in a hurry grab the new probes). :lol:

Cameron

 

[dogman dan]

Duuh, Unka Ron caught on faster than I did that you wanted to know how to actually use the multimeter.

Something we might want to make a thread on in the reference section?

Mines the common one from Harbor Freight, that sells for 3 -10 bucks.

The black lead goes in the plug labeled COM. The red lead goes in the plug labeled V (volts) Ohms, and mA whatever that is. So the lable is V horseshoe Ma

Then turn it on, and select the big dial to DCV (dc volts) On mine most tests are done set to 200, but testing an individual cell I set it to 20. If you get a negative number on the display you have black and red mixed up. Testing polarity, you are looking for a positve number on the readout when the red lead is on positive.

 

[John in CR]

I use LiMn packs on a daily basis. I also use a voltmeter as my fuel gauge. LiMn don't have a very flat discharge curve like lifepo4 or nicad. which would make voltage pretty meaningless as a gauge. LiMn typically has a 3.7V per cell nominal capacity, so for a 36V pack which is 10 cells in series your halfway point in terms of ah would be 37V, though in terms of wh. I like to stay on the safe side, so I'd use 38V at rest as my half a tank point. Also, due to the much greater voltage sag in the last 25% of the pack's capacity, I'd make sure that I'm well on my way home before voltage sags under load to 30V. Just watch your voltage while you're riding and you'll quickly learn how your pack behaves in use, especially if you keep track of the energy added back during charging. Then voltage will make a very good fuel gauge.

FWIW, LiMn batteries are typically rated with about a 500 cycle life. If you can run them conservatively you can greatly exceed that. I've put about 1000 cycles on my main pack with a 10-15% reduction in capacity. That's with cycles to only about 3.7V per cell and charging only to 4.05V/cell, but the cells I have were already used under the high demand of toolpack use when I got them.

John

 

[Uncle Ron]

One word of caution, if you touch those probes together while they are connected to the battery outputs, you will melt them (the metal, not just the plastic) with an exciting flash and create a pretty good char. Even if it seems like it is impossible to do, somehow it becomes very easy when you are thinking about your next step. Trust me on this one. That's why I took an extra set of probes (OK, a melted-tips pair) and soldered a plug to match the one on my battery charger wires. Now it's NOT going to happen again (until I can't find it and in a hurry grab the new probes). :lol:

Cameron,

Ha! I know that flash, char, and partially melted terminal, not from the same mistake, but another, and I never want to see it again. We're both lucky that the char wasn't on our hands. 36 volts DC can definitely be big injury dangerous if you don't keep your wits and knowledge about you.

 

[Uncle Ron]

I use LiMn packs on a daily basis. I also use a voltmeter as my fuel gauge. LiMn don't have a very flat discharge curve like lifepo4 or nicad. which would make voltage pretty meaningless as a gauge. LiMn typically has a 3.7V per cell nominal capacity, so for a 36V pack which is 10 cells in series your halfway point in terms of ah would be 37V, though in terms of wh. I like to stay on the safe side, so I'd use 38V at rest as my half a tank point. Also, due to the much greater voltage sag in the last 25% of the pack's capacity, I'd make sure that I'm well on my way home before voltage sags under load to 30V. Just watch your voltage while you're riding and you'll quickly learn how your pack behaves in use, especially if you keep track of the energy added back during charging. Then voltage will make a very good fuel gauge.

FWIW, LiMn batteries are typically rated with about a 500 cycle life. If you can run them conservatively you can greatly exceed that. I've put about 1000 cycles on my main pack with a 10-15% reduction in capacity. That's with cycles to only about 3.7V per cell and charging only to 4.05V/cell, but the cells I have were already used under the high demand of toolpack use when I got them.

John,

Since mine is a lead acid battery experience, I learned a lot from that mini-tutorial about LiMn. Enough to know that I'd rather avoid LiMn, if possible. After experiencing 60% amp output sag with SLAs, even 25% is too much. (g) Thanks!

 

[neptronix]

by the way... a turnigy watt meter ( if you can't afford a cycle analyst / drainbrain ) inserted between the battery and motor controller will give you lots of information. To find out how much aH capacity you have left, with a turnigy watt meter, you'd basically just connect it up... and see how far you can go on the battery until you hit 21-32v. It would tell you how many aH you used. And that would tell you the total capacity of the pack.

Determining the battery's state of charge or capacity from the voltage alone won't work well. A battery with basically no life left in it will have the same voltages if it is charged than a battery with tons of life left in it.

The difference between the spent battery and the brand new battery is that the spent battery will lower it's voltage quicker.

 

[TylerDurden]

Plenty more info about batteries at Battery University.

Resting voltage is just one measure of battery health. Testing under load is also useful.

Testers are not expensive:

http://www.harborfreight.com/500-amp-carbon-pile-load-tester-91129.html

You can also put a bunch of lightbulbs in series. ES moderator Ypedal and others use them with good results. Search for their threads on battery testing.

Some people try to measure AH with a multimeter. Amp-Hours are not Amps. Do not put the probes across the pack terminals while the probes are plugged into the Amp sockets. It's probably not a good idea to measure current with your meter, unless it's under a couple amps. A clamp-on meter or a shunt is better for measuring current.

 

[neptronix]

Um... I don't think using a 12 volt lead acid tester on a 36v lithium battery will do much for ya, unless you are just testing how good harbor freight's warranty is :lol: You won't get any useful results.

Also, batteryuniversity is pretty outdated.

 

[TylerDurden]

Um... I don't think using a 12 volt lead acid tester on a 36v lithium battery will do much for ya, unless you are just testing how good harbor freight's warranty is :lol: You won't get any useful results.

Also, batteryuniversity is pretty outdated.

For example?

 

[AussieJester]

neptronix...you not serious are you, your playin with us right?

I just bought a sperry dm6400 multimeter to be able to check the percentage of my batterys charge but I don`t know how to use it.
Sorry for the lame question but could someone tell me what setting I should use thanks.ps I have included a link to a photo of the multimeter below..... any help would be appreciated http://www.clanteamxtreme.com/forums/cTx_Reviews/Reviews/tr2rx750/4.jpg

Turn the dial one more click to the right so its on '200' to measure dc voltage of your 36v pack. Red lead in positive of your pack, black in negative... Think th rest has been covered.

KiM

 

[neptronix]

Also, batteryuniversity is pretty outdated.

For example?

Ok; batteryuniversity is not all that bad, but there are scattered facts in there from the early/mid 2000's that don't apply to today.
I can dredge up a bunch of examples but i would like to stay somewhat on topic here. I think if you look hard enough, you can find them.

neptronix...you not serious are you, your playin with us right?

I made a couple points here so i'm not sure which you're referring to. A correction is welcomed

 

[rebelpilot]

One example of Battery University being outdated:

http://endless-sphere.com/forums/viewtopic.php?f=14&t=22833&p=332155#p332155

liveforphysics wrote

'Battery University evidently is living in the 1990s.
You can forget everything it says on that page.

'A modern EV application battery has an internal resistance about 2-orders of magnitude lower than when battery university wrote that article on charging, and completely negligible self-discharge properties.

This means, a simple CC/CV supply can give them exactly what they need to charge with no fancy charge algorithms or C/10-20 cut-off's etc.

Modern LiPo (like Nano-Tech's) can be charged at >10C rates, meaning full charge in 6minutes. It also has the highest energy and power density available right now (for reasonably priced batteries at least).

 

[John in CR]

I use LiMn packs on a daily basis. I also use a voltmeter as my fuel gauge. LiMn don't have a very flat discharge curve like lifepo4 or nicad. which would make voltage pretty meaningless as a gauge. LiMn typically has a 3.7V per cell nominal capacity, so for a 36V pack which is 10 cells in series your halfway point in terms of ah would be 37V, though in terms of wh. I like to stay on the safe side, so I'd use 38V at rest as my half a tank point. Also, due to the much greater voltage sag in the last 25% of the pack's capacity, I'd make sure that I'm well on my way home before voltage sags under load to 30V. Just watch your voltage while you're riding and you'll quickly learn how your pack behaves in use, especially if you keep track of the energy added back during charging. Then voltage will make a very good fuel gauge.

FWIW, LiMn batteries are typically rated with about a 500 cycle life. If you can run them conservatively you can greatly exceed that. I've put about 1000 cycles on my main pack with a 10-15% reduction in capacity. That's with cycles to only about 3.7V per cell and charging only to 4.05V/cell, but the cells I have were already used under the high demand of toolpack use when I got them.

John,

Since mine is a lead acid battery experience, I learned a lot from that mini-tutorial about LiMn. Enough to know that I'd rather avoid LiMn, if possible. After experiencing 60% amp output sag with SLAs, even 25% is too much. (g) Thanks!

Sorry if my wording wasn't clear. I only get a 3-5% sag on a fresh charge drawing 80A from a 20ah pack. From my experience LiMn sags a lot more as you get into the deeper discharges, and I see it as a good thing because the batteries themselves give you a noticeable warning that you're getting low on juice before you actually run out. I ran for my bike for over a year with no instrumentation at all, and the discharge profile under load was a big factor that permitted such a simple rig.

If the Sony US18650V cells in my packs were readily available and reasonably priced, they would enjoy very broad use on ES, because they have a significantly greater energy than lifepo4, a solid power density, and best of all they don't require a bms or balance charging. Sadly they aren't readily available except in toolpacks, and those Makita packs are too expensive to make economic sense harvesting cells from them.

John

 

[Uncle Ron]

Since mine is a lead acid battery experience, I learned a lot from that mini-tutorial about LiMn. Enough to know that I'd rather avoid LiMn, if possible. After experiencing 60% amp output sag with SLAs, even 25% is too much. (g) Thanks!

Sorry if my wording wasn't clear. I only get a 3-5% sag on a fresh charge drawing 80A from a 20ah pack. From my experience LiMn sags a lot more as you get into the deeper discharges, and I see it as a good thing because the batteries themselves give you a noticeable warning that you're getting low on juice before you actually run out. I ran for my bike for over a year with no instrumentation at all, and the discharge profile under load was a big factor that permitted such a simple rig.

That doesn't sound so bad, I think. Just so I'm clear on this, once you start noticing the sag how much of your range is left before it cuts out (the 25% from earlier?) and how much of your speed do you lose before it cuts out?

If the Sony US18650V cells in my packs were readily available and reasonably priced, they would enjoy very broad use on ES, because they have a significantly greater energy than lifepo4, a solid power density, and best of all they don't require a bms or balance charging. Sadly they aren't readily available except in toolpacks, and those Makita packs are too expensive to make economic sense harvesting cells from them.

That's a bee-atch. Have you ever tried to track down why it's so?

Ron Shook
www.etrikebikes.com

 

[John in CR]

Ron,

That's hard to say, because I've only ridden to cutoff twice, and I rarely go past 50-60% DOD. Also, I don't ride WOT much because my big will do 60mph, so a performance decrease is generally only noticeable in that I have to turn the throttle a bit further than normal. Plus these events haven't occurred since I started running with a voltmeter on the bike.

That said, I do have a couple of examples. On one bike I had only a 10 mile pack made up of poorly matched oddball left over cells. I noticed less acceleration about 2 miles from home and made it home after dropping from my normal 35-40mph cruise down to 25mph or so. The first time it occurred I was about 5 miles from home on a 20 mile pack. I made it about 3.5 miles at WOT with steadily decreasing speed, but it was a very gradual uphill grade and into a headwind. My bikes aren't really pedalable other than some short assist on take off or up steep hills before I was running high enough current to blast up hills, so these occasions were essentially motor only.

Regarding sourcing the cells, if you can find Sony US18650V cells in factory welded blocks of 2p5s or bigger for under $.40/wh, then you've got yourself an instant business.

John

 

[randomlight]

thanks for all the great replies.A lot of it is over my head but as usual I am pleasently surprised by all the great people willing to help on this site. I think I am going to save my pennies and get a cycle analist. thanks again