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View Full Version : Use your volt meter to peak charge...


crazydave
01-27-2003, 12:29 AM
I had already ordered a 150Mah NiMh battery, but after reading TinyRC's post about charging with a peak charger, I started chargeing my stock batteries for 3 cycles. (2min. 15sec.), and was getting great torque, and 10-15 min. run times. So when I received my 150mah battery, I was in no hurry to use it.

Today I finally decided to use it, but wanted to make sure I was using it to it's potential. So I took the charger that came with my clone, pulled the timer out, and one of the AAAs, so that it was just 2 AAAs wired straight to the charging base. I monitered the voltage while it charged. It bobbed between 1.75 and 1.8 volts, then after about 5 or 6 minutes, it suddenly dropped to 1.70, that's when I pulled it off. I checked the battery, and it was good and warm like a properly peaked battery should be.

The results:
With a 3.2 motor, and 9.86:1 gearing, it ran for 40 minutes. For the first 20 minutes it spent most of it's time on it's roof. The power was incredible. I was lucky to keep it on 2 wheels going through turns, but it usually ended up flipping. After the first 20 minutes it ran for another 10 like normal, and then another 10 slow minutes. Not bad for a 5 min. charge, I'd say.

If you've got a volt meter, try it. Heck, I paid less than 20 for my digital meter, so if you don't have one, get one, they have many uses.;)
Dave

nrmcj
01-27-2003, 01:17 AM
THIS..... this i am interested in..... with my stock battery, charging from the controller, im getting maybe 3.5-5 minutes with my 3.0... i havent touched the insides of my bit or the insides of the controller... im SERIOUSLY interested in how you can do what you're doing...

what mods have you done to your charging thingy? (hehe, thingy...) any tips/instructions to help me achieve what you've done?

hogjowlz
01-27-2003, 09:56 AM
im just about done with my flux capacitor mod. the only problem is hooking it up to a fusion reactor. does anyone have an extra?

try finding "tyco" slot car springs. i have a pic of them in another thread. they help with cornering somewhat. i still flip if theres too many gs tho.

crazydave
01-27-2003, 10:22 AM
Well I haven't done any flux capacitor mods, and the fusion reactor is just not available locally, have to get one off of ebay.;)

Seriously, the car is stock, other than the battery, and the motor. I'm going to try it again today with my stock batteries. I've already been charging my stock batteries on the controller for 3 cycles, as I've mentioned before in other threads, and getting better torque, and 10-15 min. runtimes.

I just used the base to from my clone because it was already separate, and I wouldn't have to tear done a radio, but you just need the chargeing base, to plug into your car. I just wired the batteries straight to it. Some would recomend that you use resistors to slow the chargeing rate, but I know a higher charge rate means a faster disharge (more power), so I wanted to see what these batteries could handle. Part of the reason I tried this with the NiMh first, as they are more durable than NiCds.

Then while your chargeing keep your meters probes on the contacts. I drilled 2 holes in the back of the case to access them, but I'm going to instal a couple mini phono jacks thaI can just plug my probes into so I can sit back and watch.

What your watching for is a sudden voltage drop. It gradually moved betwee 1.75 and 1.78, then suddenly dropped to 1.70, and stayayed there. That's the kind of reaction your looking for. Keep checking your battery to make sure it's not over heating. (I've heard a couiple stories of melted chassis around here.) It's going to get pretty warm, so don't panick if it getts a little warm, but since it took about 6 minutes with the 150mah, then if it get's to be close 3 min. with the stock battery, you haven't seen the reaction your looking for, and the battery is getting hot then definately get it off, quick.

Hope that helps anyone.

**edit**Oh yeah, and Hogjowls, when I read your post about the spring I ran to my closet and tore apart my slot car, but it didn't even have springs. Dammit, now I have to track some of those down.
Dave

strider_mt2k
01-27-2003, 05:45 PM
Great info!
This is great for using my Quick and Dirty External Charger (http://tinyrc.com/forums/showthread.php?s=&threadid=6810)

Just watch for the indicator to go out, and push the button again! (X2)

Heck, maybe I'll ditch the controller board, and install a volt meter!

dieselboy
01-27-2003, 07:24 PM
i tried this last night but unless your car is off the charger then aren't you just reading the charging voltage? Mine ready around 1.7 if i recall but when i took my car off of the stock charger it said 1.38. I found that after 2 charger on the stock charger the battery is about at full capacity. If you go much over that it goes up to about 1.42 and then drops back suddently to 1.37volts.

Is there a way you can get teh actual battery voltage while its charging?

crazydave
01-27-2003, 08:16 PM
That's correct, you're reading how much voltage the battery is drawing, not how much it's going to put out. I'm not sure if you can check the batteries output while it's chargeing, maybe one the electronics experts around here can answer that.

I also estimated that slightly more than 2 charges would fill a 50mah cell, but if you read this Peak Charged (http://tinyrc.com/forums/showthread.php?s=&threadid=3458) post that TinyRC made, you'll see that his 50mah cell actually took 78mah. That's why I go ahead and give my batteries 3 charges. The batteries aren't getting warm, so I think they can take a bit more.

I'm going to try the stock cell right now, and see what happens. I'll keep you posted.

Dave

dieselboy
01-27-2003, 08:33 PM
ok....so if i charge my battery with my stock charger should i be looking for peak voltage or current once i take it off the charger? I know how to look for both but just wondering what would max out first or what is a better indicator of a complete charge.

crazydave
01-27-2003, 10:15 PM
Dieselboy, the voltage a cell puts out depends on the cell, I don't think the charge affects it. What you want to watch for is a sudden voltage drop while it's charging.

My results with the stock 50mah NiCd are inconclusive. While chargeing the voltage remained much more consistant, starting at 1.58, and gradually working it's way up to 1.75. My results are inconclusive, because after 5min. I still didn't see a voltage drop, in fact, that's when it went from 1.74 to 1.75. Considering I got my 150mah cell good and warm after about 5min I was skeptical of doing it any longer, and the battery was just starting to warm, so I think it was about to peak anyways. The output voltage when charged was 1.38. The longer charge rate may have been due to the batteries I charged with being drained from last night. I'll try again tomorrow with fresh batteries in the charger. I did get 25 min. runtime w/ a 2.6 motor , even if the performance wasn't as dazzling as last night. I'll remember to try it with the 3.2 tommorow too. that way the results should be more relavant
Dave

Namuna
01-27-2003, 11:17 PM
Okay, there's good info here.

- You can use the 'voltage drop watch' technique to peak charge NiMHs because (as I've read) NiMH batts have that sudden voltage drop when peaked...Not so with NiCads.

- You're using 2xAAAs which is 3.0v...But the battery was only pulling 1.7v - 1.8v while charging. Which leads me to believe that the charging batteries are PUSHING 3.0v, but the battery being charged was only ACCEPTING up to 1.8v. Good to know.

crazydave
01-28-2003, 08:29 AM
- You can use the 'voltage drop watch' technique to peak charge NiMHs because (as I've read) NiMH batts have that sudden voltage drop when peaked...Not so with NiCads.


That's interesting, because I got this idea from when I was racing 1/10th scale, and several people at the track were doing this. At this point, in '96, we were all using NiCds. I was actually wondering if it would work on the NiMh, BUT so far my own experience supports your statement.

I still think it will work with the NiCds, but more testing is order.

Also since this is the first I'm am useing either of these batteries, so I'm going to keep a log. At 50 and 100 runs (if they make it that far) I'll compare to new batteries and report back if performance has deteriated drastically.
Dave

Namuna
01-28-2003, 10:17 AM
There's possibilities here, I'm moving it...

crazydave
01-28-2003, 09:03 PM
I tried it again tonight with fresh batteries in the charger, and it was taking a much higher voltage than last night. Starting at 1.70 and gradually working it's way up to 1.85. Then it slowly began dropping. Around 3 minutes it leveled off at 1.74, I should have pulled it off then, but I expected it to drop closer to 1.70. So at 3.5 min. I realized it wasn't going to drop anymore and pulled it off. It got a bit too warm (I check temp by touching the chassis to my upper lip), so I should have pulled it at 3min.

What I'm getting is that NiMH have a more erractic chargeing voltage, where as the NiCd is more gradual, so it's harder to detect the drop. It takes some practice I guess.

Performance still wasn't as mind numbing as with the NiMH, but it was better than last night. Runtime was 21min. with the 3.2. Not bad for the stock battery, and a fast motor.

I'm going to do the NiMH again now, to see if I get the same results as last time.
Dave

crazydave
01-30-2003, 09:38 PM
After a couple days of evaluation, here's what I've found:

1. I DO NOT, recomend that you try this method with batteries, as your power source, for a couple reasons.

One 6min. charge will basically kill 2 AAAs, for practical use anyways, that could get expensive.
Once the batteries become weak, charge rate becomes more erractic, making it harder to judge when the voltage is done dropping.

for those 2 reason I think it would be better to use a 3 volt power adapter. I have a cigar box full of AAAs, so I will continue my testing with batteries, until my box is gone.

2. The voltage going to the battery being charged does affect how much the battery will draw. Chargeing with fresh batteries will push 1.85-1.90 volts, Where as drained batteries only push 1.70-1.75 volts

3. No matter what charge voltage the batteries are taking, they always read 1.38 when done.

4. Once the voltage drops below 1.5 on the AAAs, it takes nearly twice as long to charge. One 3min. charge on the 50mah battery will pull the voltage of the 2 batteries down to 2.94. Which makes me think after about 4 charges on a ZIp Zap controller, you are not filling your battery as much as before. I'm sure you could get more charges from a controller with AAs.

5. The first couple times the NiMH had a more erractic charge rate than the NiCd, which, as long as I use fresh batteries, consistantly rises to 1.85 volts, then slowly drops to 1.74. The discharge rate seem to reflect the charge rate. The NiMH seem to wind down in steps, where as the NiCd would gradually wind down just like it charged. I decided to get voltage readings every 5 min. to try to illustrate this, BUT this time the NiMH jumped to 1.85, stayed at 1.85, when to 1.87 for a sec. and then slowly dropped to 1.74. much more consistant that it was before, and the runtime voltages reflect that. Which partially proved my theory, but i wish the NiMH would have charges erractically one more time so I could see what was going on while it was running.

Here's the voltages:

min. NiCd NiMH
00 1.38 1.38
05 1.26 1.27
10 1.23 1.27
15 1.21 1.22
20 ---- 1.22
25 ---- 1.21
30 ---- 1.22


For some odd reason the NiMH had 1/100 volt more after the battery died.

Hope this information helps anyone.
Dave

bdebde
02-02-2003, 05:05 PM
Originally posted by crazydave
..... but i wish the NiMH would have charges erractically one more time so I could see what was going on while it was running.


A new battery will often charge erratically on the first charge, sometimes the first couple of charges. This is true for both nicad and nimh.

Nathan
02-02-2003, 06:37 PM
You should try to build an automatic peak charger, there must be a way.. I saw some thermistors at radioshack, i bet you could use one of those and a transistor to build a thermal peak charger. Oh, and a potentometer to tune it. The resistance of the thermistor is dirctly proportional to the temp.

crazydave
02-03-2003, 10:18 AM
A new battery will often charge erratically on the first charge, sometimes the first couple of charges. This is true for both nicad and nimh.

I've found that to absolutely correct.

I've been lifting up the PCB while charging, and found that I'm getting the batteries a bit too hot. I was doing this because of the way the voltage would jump up and down, and I was waiting for it to stay consistantly down, but now that the batteries seem to have been trained, they rise constantly up, then consistly down. So I only let it drop a couple hundreths before I pull it off, and it's getting the battery just slightly warm. If the voltage starts to drop before the battery is warm, I pop it off the charger for just a split second, and it rises right back up. I do that because I know a good peak charger will pulse the charge when a battery false peaks. I know that because I always had to use my freind's Tekin charger to bring my battery packs back to life when my cheaper Astro Flight charger would false peak. (I don't have the charger anymore, or I would be using that:) )

Nathan, there's alot going on in a good peak charger, and I wouldn't trust one that simply went by voltage drop, and/or temp. When using crude techniques such as these, it's best to keep an eye on it. (But not too close, wouldn't want a battery to explode in your eye.:D )

Nathan
02-03-2003, 05:26 PM
I know some just go by temp or drop, don't know why else they'd call it a "Peak Charger". But you are right, such a thing could be dangerous.

bdebde
02-03-2003, 09:34 PM
I use a Tekin BC112C charger for peak charging my batts. One thing I found out, the nimh batteries have a much more sutle peak. Even my high end charger has missed the peak a few times with the nimh batteries (usually single cell). It never misses the peak with the nicads though.

boho
06-27-2003, 04:33 AM
Hey folks,
this is my first post, but I've been doing this minicar stuff for a little while. For my 2 cell BCG's I use a takara/digi-q charger. It's the one that charges 4 cars/tanks at a time. I use the one that charges the tanks cause it uses "C" size batteries, which mean I don't have to keep replacing the batteries very often.
I just took the BCG charging stations and connected the leeds to the charging stations on the takara charger, didn't even sodder. Then I glued the BCG carging stations to the takara charger with super glue. It works like a charm. It even has LED indicators to tell you when it's done. I could be wrong, so please feel free to correct me, but the takaras are dual cell, or I should say they put out about the same voltage, so the charging units are easily converted.
I got my charger at toysrus in Japan. I don't know if they are sold in the states. It was about 2000 yen. that's around 16~18 dollars.
I've never timed them, but my dual cell/nimh/160mah/2.6volts runs for 30 to 45 minutes with a perfection 3.8.
PLEASE NOTE- I don't use it for my single cells because I noticed it made one get rather hot once. I don't know if it was a fluke, but I stopped charging the single cells with it. although, Before I was getting some outstanding run times with single cells too.
By the way, you guys are doing some outstanding work with this forum. It's easily one of the best.

eetoi
07-28-2003, 10:54 PM
Originally posted by crazydave

For some odd reason the NiMH had 1/100 volt more after the battery died.



I'm not saying that I really know this stuff, but nicds and nimhs both "stabilize" their voltage after they have been overdischarged. That's why right after you "kill" your battery driving a bitcharg, and it stops moving, you can get it to "budge" a little after waiting a while, then it dies again.