Power Supply Amperage for 44.4V 10AH Pack

[donorcycle]

Good people of Endless Sphere, please excuse my ignorance.

I tried to bulk charge a 44.4V, 10AH, 25C pack with a power supply that has a 1.5 amp maximum rating. This did not work. I was told the battery pack was drawing more than the power supply could put out. It seemed to shut down the power supply when I tried. How do I determine the amperage draw of my power pack for charging? What amp limit on a power supply would I need to bulk charge the pack?

Thanks

 

[jimw1960]

Approximate amp draw would be the difference between the battery voltage and power supply voltage, divided by the internal resistance of the battery. A 25C battery would have pretty low internal resistance. Say if it was even as high as1000 mohm, if the powersupply was putting out only two volts higher than the battery voltage, the inital current draw would be 2 amps, which exceeds your rating. What you need is a smart charger that can put out constant current before switching to constant voltage.

 

[neptronix]

Your power supply sounds like it doesn't have a current limiter. You are lucky that your power supply survived hooking it into that pack! Because a battery will want the voltage between the power supply and battery equalized within milliseconds!

It's much like opening up the niagara falls into your bathtub rather than pushing pressurized water through a 1 inch pipe connected to a shower sprinkler

You need a current limiting power supply.

 

[ZOMGVTEK]

You would need a power supply capable of a few HUNDRED amps to bring the voltage up to HVC on a dead pack and charge that way. The only issue with this, would be the charge rate would be astronomically high and the battery would likely start on fire before it charged properly.

What you need, is a current limited power supply, or a CCCV charger. You set the voltage, and the supply limits the current itself, by dropping the voltage. It takes a voltage differential to force current into the battery, so the Constant Current circuitry pulls the voltage down sufficiently so the current maintains at a safe level. The majority of supplies do NOT have this feature, since its really not something needed, or even wanted in a lot of cases.

That said, you can charge the pack with ANY power supply that has CC, and has a voltage range within the charge range for the pack you intend to charge. Set the voltage with the trim pot, and a CC supply will pump current in until it tapers off to the voltage you set. Obviously its a power supply, not a charger, so it never shuts down, but rather sits at the voltage you set. This isn't generally a big deal, since no current will flow if there is no differential between the pack and the charger voltage, meaning its charged. So long as it has CC limiting, you can use a 1mA supply, or a 20A supply, they both will charge, just at different rates.

The Meanwell S-350 models are popular for this, but are getting harder to find.

 

[donorcycle]

thank you so much.

I bought this one with "current limit control": http://www.ebay.com/itm/230674379413?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

Is that the same as CC?

 

[ZOMGVTEK]

Well, yeah, that will do it... It's just a little over the top if you only plan on charging a battery with it.

 

[donorcycle]

It's the cheapest thing I could find with adjustable voltage up to 50V. I also wanted meters.

 

[ZOMGVTEK]

Well, thats going to be about the only thing that fits that criteria.

The price isn't bad at all, but its still only a 100W power supply / charger. Little RC chargers are probably safer, and can balance the pack as well, but they tend to cost more than $50 when you include a power supply to power them.

 

[neptronix]

Hm. why didn't you just buy a 48v meanwell like everyone else? :|

 

[amberwolf]

That B&K should be a very good (if slow) charger like that. I use small Sorensons the same way (and have one larger one).

The really nice thing about a current limited supply is that you can use one that is much lower voltage than you need, but can handle all the current you want, and put a non-current-limited supply (with isolated outputs) that can also handle all the current you want and also is high enough voltage for what you want, in series with the current-limited supply, and use the latter to control how much current is allowed thru both. Then use the lower voltage supply adjustments to precisely set the voltage you are after.

Unfortunately you can't do it the other way, by having the current-limited supply being a lower current than you want, you can't put a higher current capable (but non-limited) supply in parallel with it to give the system more current ability.

 

[donorcycle]

It is for work, so it has to be done in 9 hours. In otherwords, speed does not matter much.

I did not get the Meanwell because I didn't want to mod it to get to 50V. In the end, it would have been more expensive and half-assed considering my soldering skills with anything smaller than 14 AWG.

It did make me think though, I have a problem at home when I leave the bike sit for a few days with low batteries. The Cycle analyst drains them. I could keep a bulk charger plugged in to top off the pack perpetually. Or could I not? Right now I am balance charging with a Hyperion, but it stops. It might be nice to have something that keeps the batteries topped off since I only have 10AH

 

[amberwolf]

Put a switch on the power wire that goes into the CA.

 

[ZOMGVTEK]

Why is the pack draining that rapidly? The CA or controller should not be powered on 24/7. Most have a small 'turn on' wire that you power on when you want the bike to run, and otherwise do not power. It should take just about no power, with this disconnected.

Also, you do not want to let the batteries sit fully charged. You will significantly decrease the life of the pack by having it sitting fully charged when not necessary. Its best to charge immediately before use, but this takes time. Sitting a day or two is no big deal, but its good practice to have the pack sitting around 3.8V/cell. Just make SURE you have nothing draining it, so the cells don't drain below 3.0 V or so.

Basically, if you don't plan on using the bike, charge it at the latest possible time so that its ready for when you do need it.

 

[donorcycle]

Ya, I guess I need a turnoff switch. I currently just have the small wire going to the positive of the battery pack. Or, I can unplug the battery from the controller. Then, I know there is no drain. The wires are easily accessible in my triangle bag. I guess a switch would be less ware on the cables and zipper to the bag.

So if I have a slow power supply (charger), would it cause harm to plug the it into the battery over night and charge the cells to 4.16? I guess it would be charging unattended and could be a fire hazard if the power supply's voltage regulation malfunctioned. Maybe I could use a timer to turn it on at 4:00am every day and then turn off at 7:00am or however long it takes to charge?

Is there any harm in leaving the Cycle analyst on constantly?

 

[amberwolf]

No harm, but it is very easy to put a switch inline with just hte CA's tiny power wire, and it's the same procedure whether it is an SA or DP model. In fact, you can mount the switch inside the CA's case, if you like, since it only takes a very tiny one, with almost no current flow thru it. Just find a spot that it will fit in and drill a hole to mount the switch (pushbutton or toggle) on so you can easily switch it on and off as needed.

Same for the controller--you can put the switch inline with it's thin power-on wire.

For a slightly more complex to build but simpler to use solution, you could use a keyswitch or master switch that turns a relay on when ready to ride the bike, and off when you are leaving it for a bit. It doesn't even have to be anything other than SPST relay or switch, since you can wire the controller's power-on wire and the CA's power input wire to the same point on one side of the switch, and run battery positive to the other. The relay and/or switch can be placed wherever is convenient.

 

[donorcycle]

I was assuming if I put a switch in line using that small red wire from the controller that goes with the battery pack, that it would turn the controller on/off including power to the Cycle Analyst. The Infineon controller came with a CA plug installed. Am I wrong?

 

[ZOMGVTEK]

The small red wire on the controller should turn both the controller and CA on. Thats the wire you would want to switch.