DIY Electric Car Forums banner

1 - 6 of 6 Posts

·
Registered
Joined
·
68 Posts
Discussion Starter #1
Hi guys, I just got my 120V 160Ah Winston LiPoY cells in. I had bought a couple of realy inexpensive zener type ballancers , that start bypassing a cell when getting over 3.6V, to test them. But is this enough?
Having only expeience charging Lead batteries, I wonder what charger I should use to charge the pack savely.
I used constant voltage on my leadbattery with a shutoff reaching a preset voltage.
LiPoY factory instructions read first a constant current at .1 -.5 ca and reaching 4V slow constant volts until current drops 1%.
I guess if charge end is set at 4V it`l be fine too.
What equippment does such a charging? Savely and costefficiently?
I`d appreciate some opinions, do I really need eqippment for over 2.5 grand?
Thanks ahead,
:)
 

·
Registered
Joined
·
2,217 Posts
Start by ditching the idea of charging to 4.0 volts. It works fine with a single cell but they will exhibit a little scatter in a series string. The higher the charge voltage and the longer the string the worse it will be. Lithium does not need to be fully charged regularly, unlike lead acid batteries that loose capacity if not fully charged on a regular basis. In fact, high ending voltage is one of the stresses that can limit the life of Lithium batteries. The capacity left unused at the top by stopping a charge at 3.5 volts and 1% of C is perhaps 2%.

I suppose simple zener regs would work, in fact you can charge with no regulators at all if you make sure the cells are initially balanced with each other. You can also install a battery management system. If you go that route please make sure the charger will safely shut down without serious overcharging despite any failure of the BMS.
 

·
Registered
Joined
·
68 Posts
Discussion Starter #3
When I bought those inexpensive zener ballancer (under 2$ per piece) I had also bought a gadget called CellLog, a whatch sized logger for 8 cells, that`s eqipped with a sensitive adc on a 4 digit volt display, multiplexed for 8 channels.
It`s designed for RC model tinkering, but incorporates a the main funktions of a battery management system, like Overvoltage, accuracy 2 decimals, undervoltage and 2 more features, that are all triggering a single alarm, consisting of an open collector capable of grounding <50V, 50mA.
The whole thing costs around 40$, and I`d need 5 of those for my 40 cell pack. 200 $ trigger anytime any cell goes undervoltage, anytime any cell goes OV. And have the cell data logged if I ever needed it.
So for less than 200$ I could have the safety of whatching all cells at all time just a lot of wiring and connectzors to be soldered.

All I need is a constant current charger and a disconnector relay.

What do you think?:)
 

·
Registered
Joined
·
4,309 Posts
initial top balance can be done pretty easily with a bench power supply available for $150 or so.... it just takes a while. wire all cells in parallel, set charger to 3.8v (for thundersky/winstons) and let them go until amps going in drop to zero..... perfect top-balance.

I don't think you want to set to 4.0v.... you just need a little higher than you expect the average voltage your charger to brings them up to once you re-wire in series. You want to increase the likelyhood that they all hit the knee at about the same time, bringing the pack voltage up enough to trigger the charger into CV and finish...
 

·
Registered
Joined
·
2,494 Posts
Also, be aware that if you use Cellogs, you will need a balancing circuit. These place an imbalanced parasitic load on your cells driving them out of balance.
I concur with the others...stay away from 4 volts. It's not worth the risk. Very little energy stored up there.

Look at the DIY charger also.

It seem from your questions, that you have not used the search function much. Do yourself a favor and do some reading here. Lot's of smart folks to help with specifics.

good luck.
 
1 - 6 of 6 Posts
Top