Vectrix's Recharging process - add your's
Whilst not wishing to argue the point,
I do feel that there is a vast difference between the manufacturers recommendations on his product and the evidence, information and practicalities which can be readily observed when using the product 'in the field'.
Without disputing what you have said. I charged my scooter yesterday following a discharge to the 'red light/battery symbol' and made the following observations.
As you can see, the charge was stopped after the first hour in order that the internal battery temperature would have time to reach the thermometer system. During the first hour there was no temperature rise.
There was no temperature rise following the second hour of charging either.
But after only ten minutes of 10 amps charge following the voltage rise past 144 volts, there was a very noticable rise in the battery temperature.
From this, I deduce that the heating of the battery begins at around the 144 volt mark. This is probably the point at which the battery is about 80% charged. It is also the point where the charge current should be reduced to prevent heating of the battery.
The last five hours, sequence 23 & 24 shows the result of charging via 'Freddy' at 0.3 amps. NO FANS and NO HEATING of the battery. This only serves to show that charging can take place, after the 144 volt / 80% charge point, without battery heating.
During bench testing of the batteries, I have noted heating effects after 80% charge with a 3 amp charge current. This heating is caused by the battery's inability to convert the charge into chemical energy efficiently (regardless of the actual current level). This is indisputable. That the heating is causing damage is also indisputable. That Vectrix have had serious problems with battery failures is also indisputable. What we have to do is deal with the problem. I know what to do, can you help me to do it?
The data provided by G.P. batteries (the copy I have) has a charge rate of between 6 to 15 amps recommended. Which is decidedly vague to say the least. As for a minimum charge rate. There isn't one. Any current will have a charging effect provided it is greater than the battery's internal losses.
I have actually charged my scooter using only 'Freddy' (0.3 amps for 80 hrs with no thermal problems and again no fans) from empty to full. I went out with zero bars showing, no miles available on the estimated mileage display and traveled for just under 30 miles without even a 'red light'. Checks, on the battery voltage were made throughout the journey, indicated that all was well. This was done to prove a point and I think I did prove my point.
Back to the post by XVectrix. The idea of allowing a charge to generate a three degree temperature rise whilst the fans are running, is unsound. As I have demonstrated, the battery's internal temperature towards the end of charge is higher than the external temperature and it takes time to work through to the outside. By the time the outer case battery temperature has risen three degrees, it is likely that the internal temperature is ten or more degrees higher still.
I am afraid that I do not trust the Vectrix software/fimware to look after the battery for the many reasons which I have already expressed. I would love to re-write the firmware, I do know how to treat batteries and they (Vectrix) obviously do not.
in theory, the charge rate can be changed using a CAN adapter, by changing the value of one of the IDs, in reality, i have yet to try this.
changing the "charge to" soc can be done manually, by bleeding the batteries down after a full charge.
it also happens automatically wiht self discharge, its part of what needing to do a balpor once in a while is all about (actual capaciy is down a bit aswell though)
During bench testing of the batteries, I have noted heating effects after 80% charge with a 3 amp charge current. This heating is caused by the battery's inability to convert the charge into chemical energy efficiently (regardless of the actual current level). This is indisputable. ...
Did you capacity test the battery by controlled discharging first?
If not, then you might have been testing cells with less than their nominal capacity of 30Ah.
I used a temp rise of 3degC over ambient (measured with an IR thermometer on the walls of the cell) as indication that a cell is full under 3A charge current on the bench.
If I remember correctly, I cross checked by repeated capacity testing (at 20A to 1.1 cutoff) that the cells are actually full, not 80% full, when they begin to heat under 3A = C/10 charge current.
Are you certain that the cells capacity was not reduced to 80% ?
Another pitfall there is that after the first full discharge/recharge cycle on the bench (actually after the first few) the cells capacity may increase again! It's due to "Exercise" and "Reconditioning" effects.
To be certain about the capacity, SOC and temperature behavior of a certain cell during (and after) charging, you need to cycle it about 3 to 5 times, until the capacity is maximized, or "plateaus". Then, without any lengthy delays, you can test the cell when it is at it's best.
About the heating after charging: It is indeed caused by heat transfer from the hotter centre to the periphery of the cell. But the energy does not only come from the heat generated during charging. At least that's what I deduct from observations on a variety of NiMH cells.
I think the increased gas pressure of a fully charged (or overcharged) cell, evident by the swelling of Vectrix cells and NHW20 cells, represents a reservoir of reactive gasses. These gasses continue to recombine in an exothermic reaction after the charging process is "officially" over.
The pressure drops as the cell converts chemical energy into heat for several hours - this causes the high self discharge rate of NiMH cells in the first 24hrs, and represents totally unneccessary "cycling" of the battery - unless you actually need that charge and begin driving immediately after charging!
Following the laws of thermodynamics, the gas pressure of a given amount of gasses (in a closed space like the cells) will be higher at higher temperatures. This is why there is more driving force for the self discharge effect in the first 24hrs if the battery is warm or hot! The gas pressure forces self discharge, the higher the cells internal pressure, the higher the self discharge, at least in the initial phase after a full charge.
The last stage of the charging process needs to be cooling, not C/3 charging! Unless the battery is already colder than 20degC or so, of course.
Does this sound normal?
I arrive home with 0km left and zero bars and 122v. I pull the right lever and turn off the ignition and plug the bike into the power cable. after the cooling sequence, the charging process starts. so far, all ok. after 1 hour of the charging process it shows 141v and about 1/3 of the bars. at 2 hours 147v, 27 deg and all but two bars. at 2.5 hours 148v 27 deg and it's in the 3amp CC stage.
A couple of hours later the bike has well and truly been off for a while....but much to my surprise it now only shows 144v. this was at about midnight. by this morning it was 141v and within 6km of normal riding even though it still showed full on the gauge, it was down to 137v.
i've noticed previously that just sitting there unused the battery drops about 2-3v per day.
Any comments on all that?
Sounds perfectly normal. The last few volts is just fluff. The voltage will settle as soon as you stop charging. Then make its way quickly to the 130s for most of the discharge.
Aircon, that's pretty much always been the norm for me, which is why I don't have any concerns at all about using regen braking right out of the gate in the mornings.
Your Vectrix will lose voltage every day that it sits unused, and if it sits long enough to lose down to 80 volts or less, it's toast, because the charger will no longer recognize it. That's why I've always used a hardwired timer on the circuit that I keep my bike plugged into at home. Since the timer cuts the circuit to the bike every day, and turns it back on every night, the charger will come on, assess the battery voltage, and charge if needed. If you simply leave the bike plugged into a live source without ever disconnecting it, it's not programmed to self check and correct periodically. It will eventually run down.
"the charger will come on, assess the battery voltage, and charge if needed."
As far as I know, that isn't how the charger works.
When you ride the bike, it monitors the consumed Ah. Then when you charge it, it delivers that same amount.
It cant measure the self discharge in the battery. So if it is just sitting there, it will have a full gauge and just go straight to the EC phase of the charge. That few minutes of 3A might be enough to keep you out of trouble for a long while, but eventually you will need to take it for a spin and drain it to the battery indicator to reset the charger to zero.
That is my understanding anyway, the charger does not use the voltage as an indication of SOC
Thanks for the clarification gentlemen.