SparkFun Forums

[Grimm Spector]

ok, got a max1555 with the breakout charger board, wired it up with the battery + to the BAT term, plug in my USB either through a USB charger wall adapter or a computer, and sometimes right when I plugin I get a light, and sometimes when it's unplugged I get a brief blip of light, but if i leave it plugged in...no light...doesn't seem to charge...I've multitestered the battery amperage is 300 mA or so, which doesn't seem to be even close to a max charge, though the voltage is registering at peak. I know the MAX is rigged to shut off when voltage reaches a certain point.

Am I doing something wrong? Or is the battery full and my meter is busted?

[Grimm Spector]

after a few tests I've got 6.78 amps across the terminals, which seems kinda...high...

either way I have 3.8 volts steady across the terminals and when hooked up to a load it powers it fine, voltage drops normally as per the resistance of the load, no ill effects, so I can only assume the battery is fine since it runs a load. It is normal for the batteries here to come with a full charge??

[ohararp]

Grimm, full charge is at approximately 4.2 volts. The 1555 should slowly ramp up the current and voltage to the battery reach a certain point and hold steady. Good place to also look for help is www.rcgroups.com. Make sure you use a protection circuit module (pcm) with your battery to protect from shorts, extreme discharge and charge.

[Grimm Spector]

Grimm, full charge is at approximately 4.2 volts. The 1555 should slowly ramp up the current and voltage to the battery reach a certain point and hold steady. Good place to also look for help is www.rcgroups.com. Make sure you use a protection circuit module (pcm) with your battery to protect from shorts, extreme discharge and charge.

well if it.s 4.2v I'll have to modify how I do my electronics significantly, any idea why it's telling me it's got 6 amps? I know from working at a battery store that an ammeter doesn't tell you the true useable capacity of the battery but it's a 2Ah battery which means 1.85 is what I would expect to see without a load.

So why is my Max 1555 not working? The red light flickers once whe unplugged as if the cap is full and discharging when I disconnect the USB...

[ohararp]

Grimm a couple of things:

1. Although SFE puts out great products I have noticed that sometimes not all of the SMT connections are properly made. Check to see that there are no "dry" connections between pins and pads.

2. Are you using the 2000mAh lipo battery from SFE? If so, this battery is spec'd at "2C continuous discharge" and "3C max discharge". Where C is the capactiy of the battery in Ah's. Therefore this battery can deliver 3 x 2Ah = 6 A of current. More than likely it cannot deliver this continuously nor at the Capactiy of 2000 mAh (a detailed data sheet would spec this out).

3. When charging check the voltage at the battery terminals. The voltage should rise slowly from the initial battery voltage to ~4.2 V. From the MAX1555 data sheet - "When charging stops, VBAT = 4V".

4. Please be very careful with this battery chemistry. Do not short the terminals in anyway (lots of potential energy in this package). Do not discharge cell below 2.5V, do not charge above 4.2V, and do not discharge the battery beyond the 2C rating. Consider using a PCM to help prevent these situations from occuring.

[Grimm Spector]

Grimm a couple of things:

1. Although SFE puts out great products I have noticed that sometimes not all of the SMT connections are properly made. Check to see that there are no "dry" connections between pins and pads.

2. Are you using the 2000mAh lipo battery from SFE? If so, this battery is spec'd at "2C continuous discharge" and "3C max discharge". Where C is the capactiy of the battery in Ah's. Therefore this battery can deliver 3 x 2Ah = 6 A of current. More than likely it cannot deliver this continuously nor at the Capactiy of 2000 mAh (a detailed data sheet would spec this out).

3. When charging check the voltage at the battery terminals. The voltage should rise slowly from the initial battery voltage to ~4.2 V. From the MAX1555 data sheet - "When charging stops, VBAT = 4V".

4. Please be very careful with this battery chemistry. Do not short the terminals in anyway (lots of potential energy in this package). Do not discharge cell below 2.5V, do not charge above 4.2V, and do not discharge the battery beyond the 2C rating. Consider using a PCM to help prevent these situations from occuring.

yup I know lots of PE in the pack, so I don't wanna screw it up, I've been careful not to short the battery, I nearly did :-\ when utilizing the battery I intend to bridge the contacts with a small PIC and watchdog the voltage and if it gets to 3.0 which if I'm not mistaken is the lowest voltage with a load recommended for operation? I plan to make the small PIC send an interrupt to tell my system to shut down and it'll disengage everything from the battery. I'm planning on mainly wiring this up to charge from solar panels and regulating it to the 5 V input, when I've got it properly setup.

In the meantime I just need to wire this properly, could you tell me how to wire up the 2000 mAh I've got, to the Max1555 board without a load system, I've never built a charging system before, only used disposable cells in the past for power. Thanks.

[ohararp]

I pulled out my max1555 breakout board. If you only want to charge your battery; Simply Hook the 2 pin BAT/GND up to the battery. I use the board purely as a charger just like this. I would show this setup with the led on but the battery is currently fully charged and is reading 4.15 V.

[Grimm Spector]

just to be sure i'm looking at this right that's + to the BAT and - to the GND? I'm very tired but I think that would drain my battery through the USB's ground connection wouldn't it? Shouldn't it be - to BAT and + to GND? ... clarify for me for the morning if you could thanks.

[Kuroi Kenjin]

That doesn' t make sense? If you hook it in series (- to BAT and + to GND) you're going to force charge out of it. Batteries charge in parallel (pretty much anything does for that matter). It should be + to BAT and - to GND. It dosen't discharge through the board/USB because it's a higher voltage.. if it was less then it would definately discharge.

[Grimm Spector]

That doesn' t make sense? If you hook it in series (- to BAT and + to GND) you're going to force charge out of it. Batteries charge in parallel (pretty much anything does for that matter). It should be + to BAT and - to GND. It dosen't discharge through the board/USB because it's a higher voltage.. if it was less then it would definately discharge.

really, just seems I'm giving a route to ground for the electrons in my battery so I don't see that as being a great plan...but if the two of you who probably know much more about charging a battery than I do can tell me that it's correct, then I'll give it a shot ... outside...

Hey, I just reread that, you spurred my sluggish morning brain into action, potential on the USB port isn't the same as the potential in the battery, therefore current shouldn't flow because the electrons want to move to decrease the energy in the system due to enthalpy not increase it...

told you I was tired, thanks guys I feel much more awake now.