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Charging Holden Volt off battery bank overnight

PostPosted: Tue Jan 31, 2017 9:31 pm
by craby

I know I haven't posted for awhile, but I was looking for some views in relation to charging my Volt off the house bank overnight.

Basically at the moment I can usually make it home from work so that there's about an hour or two of good usable PV power at the end of the day. I set the car to the 10amp setting, which draws about 60 amps DC, and takes around 6 hours to charge the car.

Alternatively I can use the 6amp setting, which draws around 30 amps from memory (it's 1.5kw vs 2kw), but it takes 10 hours.

I have a 940 a/h bank of gels that are rated for about 3000 40% discharges, so if I charge the car at 6A overnight, I see that I draw down about 350-400A/H overnight, which includes the house load (at this time of year it's 5 fans running all night). That said, 1.5kw draw is about what I'd pull if we had the PC and TV gear going on a Friday night, so it's not that much different from a power drain perspective. I have 10kw of PV, so I can easily recoup 400AH in a few hours, and I come home to find the system in float each afternoon.

Anyway, my question is this. Would it be better to charge longer and use a bit more power, or draw less power overall but at a higher rate of charge? My understanding is that there's more power used to charge at the lower rate to overcome resistance, but I don't know the exact difference.

My gut feeling is pulling less overall at the higher rate is the way to go, but maybe a lower draw rate over a longer period is better for longer battery life?

I'd appreciate any views on the matter. I wouldn't have attempted this with my old lead acids, but the new gels seem to be able to be cycled more deeply, and like I said, the draw rate at the 6A setting isn't far off what we'd be drawing anyway with the TV and PC on, so it seems to be much of a muchness in that regard.



Re: Charging Holden Volt off battery bank overnight

PostPosted: Tue Jan 31, 2017 10:18 pm
by davidg
craby wrote:maybe a lower draw rate over a longer period is better for longer battery life?

This is the thing to remember with lead a lower current drain is better for the pack (peukerts law/exponent) which in essence means that lower current draws over longer period will leave the battery pack at higher state of charge compared to the same amount of power drawn in shorter period of time.

Re: Charging Holden Volt off battery bank overnight

PostPosted: Wed Feb 01, 2017 1:08 pm
by offgridQLD
I have some experience with this as we charge are Imiev offgrid and different charge rates depending on weather conditions and when we need to use the car and what trip we are taking.

David already said what i was going to suggest for the same reason. If your not time challenged then charge at the slower rate. Biggest reason is its easier on your lead acid. They will spend less hrs sitting at the lower SOC before the sun comes up the next day and be less stressed by the lower current draw. This as other benefits to as it frees up more breathing space on your invrters output MAX encase you need to run a few spike loads. There is also less stress on your inverter, car charger and house battery's.

Though if your in a hurry or are charging in the day time some times its well work charging at the faster rate. Some times when its sunny in the morning but I think there could be a storm drifting in later that day . I will crank the charger up to 3200w to feed more in that morning. No point having 8200w of pv idling along at 1500w for hrs and then having to pull several hrs of it from the battery when the sky is black. If you can be feeding 3200w to the car that early and get the job done.

I have my Imiev on faster speed 3200w today because due to appointments I had to go to town and back 3 times in the one day but typical scedual is just having it idle along at 1500w over the day and that works out fine for my daily needs.

On the subject of plug in hybrids. I was giving the Mitsubishi out lander some thought today discussing it with my wife. We currently have two cars a 2010 isuzu Dmax 4wd ute 8lt/100 consumption for long trips and towing (a small 380kg campervan and a bit a light trailer work) and the Imiev. 90% of out driving in the Imiev as the school run 2x a day two 25km round trips. 250km pr week with the odd longer trip thrown in 60 - 100km every now and then. The ute sits ide most days cost us insurance and registration along with a annual service that i perform myself but still a cost + its a long bugger of a thing taking up space in my shed + my wife hates driving it duel to its size and being a manual :lol:

Our EV needs could be catered for with the Outlander and it has 50km pure battery range. So 25km school run to town would be all battery with a charge over the day offgrid then a afternoon 25km school run.

I do have a bit of a emotional attachment to the little Imiev as its a great little car but the smart choice could actually be the Out lander for us and I would end up with some change from the two cars.

Re: Charging Holden Volt off battery bank overnight

PostPosted: Wed Feb 01, 2017 6:52 pm
by craby
Hi again,

Thanks everyone for your replies, that was really informative. Time's not a big deal for me when it's an overnight charge, but it's a different way of thinking for me to draw down that much overnight, since we used to baby the old lead acids so much to keep them above 80% all the time. Going to a smaller capacity bank was sized so that we could meet the load from the Volt overnight if we had to, and still sit within the 35-40% draw down on the batteries to keep the lifespan up.

The sun is just setting now so I'm going outside to switch back to the 6A setting. Good advice. It just seems weird to pull power like that out of them at night, but I guess it's well within what they're rated for, and I may as well take advantage of it.

Offgrid I did look at the Outlander, but I'm beginning to think my next choice would be a battery only EV with a much longer range. I have to do 160km's a day, but I can manage that with only about 1.5l of fuel as I charge at both ends. I was looking at used Volts the other day, and I saw some in the $25k-$30k range, which made me tempted to get another one as I'm thinking of a second car. The other thing I was waiting for was to see the specs of the new Camry Hybrid that's coming out of Japan this year. If it's got a whole new hybrid drivetrain like the Corolla did, it could be worth a look as well.

If you can get a Volt on the cheap, it'd pretty well pay for itself. I know ours is. My total fuel and electricity bill for 2016 was $710.45 after doing over 30,000kms (I sometimes pay for electricity at one end of the trip each day). Compared to about $5000 a year for my old Accord, it's worked out nicely.

Thanks again for the advice, I'm glad to hear I'm not doing anything wrong.



Re: Charging Holden Volt off battery bank overnight

PostPosted: Wed Feb 01, 2017 7:43 pm
by offgridQLD
Sounds like the Volt is working out very well for your situation. Yes it can feel funy sucking away at your house bank to fill your car. Even I feel funny about it at first (though I don't do it often) and I have lithium's that are not to fussed about SOC. As long as you know your house banks SOC and keep track of the load so you can keep it within a manageable scope that's within spec of the bank then you should feel to guilty.

My big concern with a BEV / hybrid is baking the traction pack. Heat is a evil thing for lithium cells. We can baby our Imive as it gets charged in the cool insulated room at about 25c even in summer. We drive it and then if its parked its parked its always parked in cool shaded places.

Out ute gets absolutely baked taken around Australia some places must be close to 50C and it's unavoidable where you park it and for how long some times. You return to your car with your thongs stuck to the melted road , leave it at the beach carpark all day frying in the midday sun.

I'm just thinking of the outlander that basically has a slightly smaller imiev battery with the same cell slung under it in a box. On a drive from say Brisbane to Adelaide over summer. How would that traction pack be feeling after humming along on the freeway for the past 10hrs with all the heat from the 2lt petrol motor, exhaust blowing onto it and the 1000s of miles of black top you have just covered radiating heat up onto the traction pack. Cars realy are a terrible place to house a battery in a climate like AU.

I think I would just feel so guilty of how abusive I was being to the battery.....some times ignorance is bliss. I think I need one car I can absolutely abuse and have little concern for....sorry Isuzu :lol:

On the subject of saving money or cars paying for them self. You really have to do a hell of a lot of km to make that come true. Just the registration and insurance cost on a 2nd car is about $1000 + a good $200 or so for diy maintenance and tiers. If you only travel say 300km a week 15,000km PA in a reasonably efficient small car 5lt/100km at $1.30lt is $975 of potential savings to be had.

So the most you can save is about $1000 on fuel and say $200 in maintenance (assuming your EV electricity is free) having to spend $25 - $30k to do that as a 2nd car isn't going to work as even the banks will give you 3.3% pa on that lump sum or $1000 pa on 30k. Though if your doing 50 -60,000km pa then it can start to work.

Though driving in silence and the overall driving experience and self insurance of a off grid EV is worth a lot of money :D