High speed balancing with high currents using Akumons
A simple solution using the automotive 12V relay and the 12V halogen bulbs.
Simple solution to make a 24V battery pack
Two 12V batteries (here 12V 60A) are packed together. A plastic handle is mounted too, to allow easy carrying of the pack.
A high power fuse (400A) and two Akumons are mounted inside a plastic box.
Replacing SLA in the UPS with LFP
Multiply the performance of any UPS (Uninterruptable Power Source) by replacing the SLA (Sealed Lead Acid) batteries with the LFP (Lithium Phosphate) technology.
The old battery pack on the photos is from APC 1000VA rack UPS model. The nominal capacity of the pack is 24V 14Ah (2S2P configuration). The real energy available from the pack is max 250Wh. This means that a 250W computer may run up to 60 minutes from the UPS with the original SLA battery.
The Charging 12 pcs of 20Ah cells
The initial charging of the number of cells. For charging we are using a laboratory power supply capable of 5V 100A. We set the nominal voltage for 3.8V and connect the cells.
These 12 cells in parallel make a big 3V 240AH cell together.
Warning: when charging in parallel, it is a MUST (!) to double check the correct polarity of the cells. Connecting a cell in reverse polarity will cause a dangerous short circuit that may result in a strong sparking. BE EXTREMELY CAREFULL (!).
Warning: we suggest to wear protective eye-glasses to avoid a possible damage to the eyes by sparks or melted metals in case an accident happens.
Charging 12V batteries in a parallel pack
Six 12V 60AH batteries chargered with 12V 100A charger. The batteries are in parallel and make 12V 360AH pack.
Hint 1: Note that the terminals of the charger are connected on the oposite sides of the pack. This is a small hint to make sure that all the batteries will be chargered equally during the high speed charging.
Hint 2: Additionally after the charge cycle is finished, it seems good to let the batteries rest and equalize over 1 or 2 hours and then make another charge to full. This may be repeated 2 to 3 times to make the batteries in the pack equally charged.
Cleaning all the battery terminals with a wire brush before you connect them up makes a remarkable difference to how the pack performs. ThunderSky cells use bare copper and aluminium for the terminals which quickly builds up an oxide layer (Al2O3 is particularly pernicious). In one extreme case (a couple of years back) the oxide layer caused so much resistive heating at some terminals that there was heat discoloration on the interconnector, melting of the plastic around the terminals, and fried BMS modules!
Lithium-iron-phosphate batteries from Thunder-Sky …. as they heat up, they can swell and crack the casing if they’re not squeezed together.
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| — | Solid casing for the LFP battery packs needed: Lithium-iron-phosphate batteries from Thunder-Sky. They aren’t as sensitive to temperature, but they do need to be kept under pressure. This bracket is part of a vice I’m building for the batteries. As they heat up, they can swell and crack the casing if they’re not squeezed together. (source) |
RT-BMS Cell Balancing Modules (CBU) mounted on cooler
A model instalation of 4 CBUs mounted on a cooler. Keep in mind that insufficiant cooling of the CBUs will lead to overheating and the balancing performance will be limited.
“Batteries must be kept upright. They are very dependent on orientation.”
This statement is not correct, TS cells can be laid on their sides, I have confirmed this with ThunderSky several times and I have used them on their sides in several of the EV conversions I have done with no ill effects.
ThunderSky does warn though that if the cells are over charged the vent can open and if they are on their sides the electrolyte can leak damaging the cell. If you use a good BMS you should never overcharge the cells so this shouldn’t be a problem.
Battery assembly using a packing straps
The simple solution to assemble individual cells into the battery packs: strapping them together by the plastic staps used for packing of parcels.
Connecting 12V batteries to make a high capacity battery block
The drawing with idea how to connect the 12V batteries into high voltage (48V), large capacity battery block. Each battery is protected by a fuse to prevent from the damage of the whole string. The BMS manages each parallel block of the 12V batteries.
The 12V battery protection circuit to disconnect high-currents
Using a high-power relay or contactor it is possible to protect the battery against deep discharge when draining high currents.
![12V battery protection - Battery guard (accu saver) 12 V/DC [M148A]
Please see a useful link for a simple battery protection circuit. KEMO Battery guard (accu saver) 12 V/DC [M148A]. Please note this protection works up to 10A currents. It cannot be used for high-current solutions.
Note: based on KEMO specifications the peak voltage for M148A is max 15V. When you plan to use this device please do not charge above 15V.](http://24.media.tumblr.com/tumblr_l5xabpVadK1qa2swjo1_500.gif)
12V battery protection - Battery guard (accu saver) 12 V/DC [M148A]
Please see a useful link for a simple battery protection circuit. KEMO Battery guard (accu saver) 12 V/DC [M148A]. Please note this protection works up to 10A currents. It cannot be used for high-current solutions.
Note: based on KEMO specifications the peak voltage for M148A is max 15V. When you plan to use this device please do not charge above 15V.
When you connect the motor controller to batteries severe sparking often occurs. This is caused by the internal capacitors inside the motor controller circuits. The PDF file explains a simple method how to prevent sparking.
The RT-BMS allows to switch on the anti-spark connection before the main current switch is connected. (RT-BMS Master unit - connector B4 - Antispark Current)
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