P1080, P3022

I have a 24v 5a charger, I could set the modules up in series groups of 3 paralleled, if they'd handle that, but I'd still have one odd module left

 

That was my thought, they've held it together this long......

My daily is still on it's original battery, I'm amazed @ 223k, but it sees mostly highway miles, so the battery doesn't stress much.

 

So, I went the smarter way and elected not to try rigging it (car still not smogged/reg'd). I got a new VOM for home now, and after having set resting for a week this is how both packs read today:
VOLTS @ rest 1 week

PACK 1 (car) PACK 2 (donor)


A1. 7.76 7.79
A2. 7.76 7.77
B1. 7.76 7.78
B2. 7.76 7.76
C1. 7.76 7.76
C2. 7.76 7.76
D1. 7.77 7.73
D2. ** 6.48 7.76
E1. 7.76 7.75
E2. 7.67 7.75
F1. **6.51 **6.48
F2. **6.49 7.75
G1. 7.77 7.75
G2. 7.77 7.75
H1. 7.78 7.75
H2. *7.54 7.75
I1. 7.77 7.76
I2. 7.77 7.75
J1. *7.41 7.75
J2. **6.49 7.76
K1. 7.77 7.75
K2. 7.77 7.75
L1. **6.49 7.76
L2. 7.76 7.76
M1. 7.76 7.76
M2. 7.82 7.76
N1. 7.76 7.76
N2. 7.76 7.78

I am considering ** to be a bad module due to shorted cell, & considering * to be questionable due to high bleed off. Sound reasonable? This is as- pulled untouched (buss rails removed) out of both vehicles. Initial thought is that the donor battery is a much better candidate to repair. Alphabetically paired as "blocks". When pulled, pack 1 was 7.85 area, pack 2 7.81 area, excepting the bad modules.

 

Hybrid battery charging on a budget

1:1 ratio variac box I built yrs ago (voltage control adjustment) powering the 120v secondary of transformer, primary of transformer jumpered as 480v, both ends rectified with double 1N4005 diodes (doubled as failsafe), then diodes wired to 100w 120v bulb (for current limiting control) to 0.3 amps, then to battery +. Battery - is wired thru a 0.1ohm resistor (for accurate true RMS current measuring), back to center tap of transformer secondary, creating two 240v half-cycle charging circuits. Slow but safe, & for an old electronics junkie scrounger like me with hoards of parts, pretty cheap to make.

 

I can put a fan on it, but it doesn't feel like its making any heat so far @ around 1/4A charge current

 

Success! After a bit of a learning curve researching nimh batteries , and some fabrication of charge & discharge tooling, the reconditioned pack is back in the wife's car & going strong!
I've seen a lot of posts about people spending quite a bit using hobby chargers to do 2 or 4 modules at a time. The setup I built was inexpensive & fully adjustable voltage and amperage control, to charge/discharge any combination of modules or a full pack! I can safely charge them @ 0.65A for 8-10 hours (keeps the heating at a minimum), or leave them on a 0.2A trickle indefinitely.

 

For cooling as a safety measure, I used a 6" computer fan mounted to a small cardboard box, a slit cut in the opposite end to match the belly pan of the battery. Voila! Forced air cooling around all the modules!

 

Having finished up the wife's car I moved on to my own, the process was much faster this time! Both cars up & running, getting over 45 mpg

 

Construction was done in a few hours, roughly a week in the research/engineering, a few days of cycling/charging/testing in afternoons after work.

 

WARNING: THIS CHARGER IS NOT AUTOMATIC AND SHOULD BE MONITORED CLOSELY UNLESS BEING USED AT A 0.2 AMP RATE OR LESS!!! PRE PLANNED TIMED CHARGE CYCLES SHOULD BE USED BASED ON STATE OF CHARGE & RATE!!

I've already put a few pics in a previous comment, including a schematic diagram. Basically I used a 2 amp variac (variable transformer) box, plugged into the wall, which fed a 0.5KVA control transformer, on the secondary (120v) side. This created a step-up transformer, with the primary side center tap jumpered as 480v. The battery negative and wall power ground are also connected to the center tap. Now, each end of the primary is connected to a pair of 1N4005 diodes is series (doubled up for safety in event one fails), all diodes polarized as flowing out from the transformer, then the two diode pairs are connected together @ the downstream ends (effectively creating two paralleled 277v half wave charging circuits), and to the center (hot) lug of a 100w light bulb. The other end of the light bulb goes to the battery positive. Now, the variac is then adjusted to lower the voltage into the step up transformer to obtain the correct charging voltage as 277v is a bit high. The 100w bulb provides not only a visual aid of charge rate, but a current limiting resistance, relative to the voltage you set. Do not exceed 250v to the battery or you will over volt & pop the diodes!! This could make a big kaboom when the battery sees AC voltage!!

You need to use a good quality true RMS meter for measuring current & voltage, on a completely discharged pack (6v per module) I would set it up to charge 0.65A for 8-10 hours (safely), then watch it until I achieved 8.2-8.4v per module, at this point if they aren't charged evenly be careful of overcharging, in that case if would be better to drop to a 0.2A rate (not enough current to harm full modules) and float the remaining modules up.

Charging partial packs will require lamp wattage & voltage adjustment to achieve desired currents.

WARNING: THIS CHARGER IS NOT AUTOMATIC AND SHOULD BE MONITORED CLOSELY UNLESS BEING USED AT A 0.2 AMP RATE OR LESS!!! PRE PLANNED TIMED CHARGE CYCLES SHOULD BE USED BASED ON STATE OF CHARGE & RATE!!

 

I'm actually working with my father on a possible production design for an affordable one with better safeguards. This creation I made did the job, but can be very dangerous if misused.

 

For discharging, I used two 100w bulbs in series across the pack, which gave me around 0.7a rate so as to not overheat the pack. I made a spreadsheet to record readings & checked it at 15 minute intervals on the first discharge. Stopped when the first module dropped to 6v (minimum voltage of 1v per cell), then used 10w 10 ohm resistors on remaining individual modules until all were drained to 6v. This helps to erase any memory, hence "conditioning". 2-3 cycles should pretty much make it or break it as far as what modules can stay or go in the pack, the goal being reasonable capacity, & best possible balance of modules. Much like doing a compression test on an engine, look at readings, anything that's within 0.5AH capacity of each other as a group should be ok, any module that dies sooner (others last longer than .5h after it reaches 6v) or a module that greatly outlasts the rest of the pack, is excessively out of balance.

 

That would work, if you only have 220 & not 240 you might be limited to a lower max available charging current, & you would only be able to "pulse" charge on a half wave cycle, since taking both hot legs to neutral would result in too low of a voltage, so your charging time may be significantly altered.. I had to go with the step up because I'm off grid & only have 120v currently, though I'm upgrading to twin stacked inverters so I'll have 220 then!