Newbie charger question

[ebike11]

Hi guys
I just had a quick question about chargers.
If a charger's voltage is factory set at 36V does that mean it can "generally" charge ANY type of battery pack that
is rated @36V even if some chargers have different charging Amps which determine the charging speed?
Thanks!

 

[icerider]

You are interested in two possible issues.
1. Does the charger final (end of charge voltage) exceed the voltage that is safe for your battery ? This is usually listed as the charger MAX voltage.
2. Does the charger's initial (start of charge for low battery) current exceed the current that your battery can safely accept. This is roughly (rated charger wattage / charger nominal voltage).

Let's take the first one first ... most advertised charger voltages are stated in terms of the battery's NOMINAL voltage. So, for example, the charger for my LiMn battery pack is called a 36V (or 37V) charger. This is because my (10s) battery is 37 volts nominal (3.7V per cell times 10 cells in series). This charger's final voltage (when the pack is full) is 41.6 volts or 4.16V per cell, comfortably below the max 4.2V per cell that LiMn batteries will tolerate.

Now, consider the state at the beginning of charge. You need to know that the charger's CURRENT output at the start of charge is below what your battery can safely tolerate. This charging rate is frequently discussed in terms of "C" . A 1C charging rate would fill the battery if is continued for 1 hour. In practice, the current delivered to the battery tends to drop as the battery approaches full charge. So, for example, for my 10Ah 36V battery, a 10A current flow at the start of charge would be a 1C charging rate. This would be too high for my batteries, which recommend a charging rate no higher than 0.5C. In fact, my 36V charger produces about 3A of current at the start of charge (0.3C) and the charger is rated at 120W (which is pretty close to 3A * 37V). This charger will charge my battery from near-empty to full in about 5 hours.

Now, the best way for you to find out would be to get a multimeter and READ the initial current at start of charge and the final charging voltage at end of charge. The big danger in this method is that the initial current may be high enough to blow a fuse in the BMS.

One REAL caution --- while your battery is getting to full charge, monitor the voltage and be sure that as the battery gets full, the charger output does not go above the battery max voltage. For example, for a 10s LIMn or LIPO, the max voltage per cell is 4.20 and the charger voltage needs to stay below 42V to be safe.

 

[eva-michael]

36V is just a rated voltage. It does not mean it just output directly 36V. According the the feature of chemistry of different type of battery, a suitable charge programme(Charge Curve) will be requires. Check the label in charger, it should show you a dedicated type of battery which the charger is specialized for.

 

[ebike11]

Thanks for the replies!

I should have mentioned that my pack has no BMS
it is 10s pack..so 42V hot off the charger.
The cells are quite large. They are car cell batteries used in hybrid cars.

I just have a cheap aliexpress charger that I want to try on the pack. Its rated and was sold as a 36v charger
Im sure the charging amps of it are very low so it will take a while to charge Im guessing

 

[icerider]

Im sure the charging amps of it are very low so it will take a while to charge Im guessing

If the charger is connected to a battery much larger than it was "intended" for, a couple of things may happen:
1. If the charger is current limited, then it will work fine but will take a LONG time to charge the battery.
2. If it is NOT current limited, it will try to source too much current and it will overheat, possibly badly -- it might also blow an internal fuse (if it has one) -- or just let the magic smoke out.

With a multimeter, you could hook it up and check the charging current and disconnect the charger if the current is much above (Wattage / nominal volts)...But, where the battery is that big, the fuse (if there is one) may be quicker than you are.

Someone with broader experience than I have may know whether the typical vendor-supplied charger is current limited.

Or you could invest in "the last charger you will ever need" -- http://www.ebikes.ca/product-info/cycle-satiator.html

See how it would charge your battery using the charger simulator -- http://www.ebikes.ca/tools/charge-simulator.html

buy it here http://www.ebikes.ca/shop/ebike-parts/chargers/cycle-satiator.html may be out of stock ??????

I have no connection to the vendor and do not own this charger, but if I had a large custom battery, this is the charger I would buy without hesitation.