Battery Choices

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hyve
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Battery Choices

Postby hyve » Sat Mar 15, 2008 2:51 pm

Having spoken to Ian Goodman about his LiFePO4 batteries at Mansfield I'm curious whether other members have either any knowledge or experience with this type. The figures are very impressive.

Looking at a very comprehensive page on lead acid batteries on the diy electric car website I see that we have a real conundrum with these. If you get deep cycle batteries they are good for travelling along at a steady pace, delivering a good supply of amps until well down. But they're not designed for heavy discharge, such as when setting off from a traffic roundabout in an attempt to join the circus before getting mown down by the rush from the previous entry road. One of these is a daily hazard on my route.
If though you use ordinary car batteries they can cope fine with this, but won't like the 100 or so amps continuous you'll need to maintain speed thereafter.
This suggests to me that to use lead acid you need a set of each, doubling the awful weight penalty which batteries incur.

So what happens in reality ? I'd like to know what you regular EV drivers do, if you're using this old technology that is. Am I taking manufacturers' recommendations too literally here ?
Peter Ph

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Peter Eggleston
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Postby Peter Eggleston » Sun Mar 16, 2008 9:32 pm

I use lead gel deep cycle batteries, and providing your gearing is right there is no problem keeping pace with other traffic. Because with an electric motor you have maximum torque form zero mph, which internal combustion engines do not have, acceleration from rest is much better with electric. Merging with traffic is also much easier because you can ease off on the throttle on your approach and then accelerate instantly without the need to change up or down gears.
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geekygrilli
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Postby geekygrilli » Mon Mar 17, 2008 6:28 pm

Are these a good option? UPS batteries 105Ah.

http://cgi.ebay.co.uk/DEEP-CYCLE-BATTER ... dZViewItem

I'd like to know, because I doubt my first set will last too long.

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ChrisB
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Postby ChrisB » Mon Mar 17, 2008 8:16 pm

They will be OK although I feel they are expensive, I've seen these types of ex UPS batts on e-bay for £20 each and if you buy in bulk I've seen them as low as £10 each :shock:

I would be careful as UPS batts are generally on a float charge system and this "can" cause the batts to dry out and lose capacity.

Also UPS batts are really designed for long duration float charges and then a steady discharge once in a while, you may find they wont be up to carrying out cyclic opperations in a EV as well as a propper cyclic battery.

Having said that if you can pick them up cheap enough then it dosnt matter but I wouldnt pay £43 each for them (which is what the ebay price is currently for those you linked to)

Dont forget these folk who have these for sale are almost certianly getting these batts for NOTHING :wink:

ChrisB
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Peter Eggleston
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Postby Peter Eggleston » Mon Mar 17, 2008 9:36 pm

I have been using a full set of this type for 4 years on my truck and they are still as good as new. I think they are brilliant. As ChrisB says though you can get them a lot cheaper. There are currentlly some on Ebay at £35, but haggle for them as the guy has 1500 of them. I paid as little as £11 for mine.
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geekygrilli
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Postby geekygrilli » Mon Mar 17, 2008 11:14 pm

Excellent, thanks for the advice..they're not needed just now. But now I know what I am looking for if some come up for sale cheap!

hyve
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Postby hyve » Wed Mar 19, 2008 9:22 am

Peter Eggleston wrote:I use lead gel deep cycle batteries, and providing your gearing is right there is no problem keeping pace with other traffic. Because with an electric motor you have maximum torque form zero mph, which internal combustion engines do not have, acceleration from rest is much better with electric.


Thanks for this Peter, but in order to answer my question as to how deep cycle batteries cope with the huge amp draw needed to get that famous 'max. torque at zero revs', I really need a bit more info.
Such as: what battery capacity do you have ( how many amp/hours total) or what weight of batteries do you carry ? What power is the motor ?What does the vehicle weigh all-up ? How often was it used over this four year period ( how many charge cycles)?

It would be simpler for someone with the knowledge of batteries to just post the answer !


Added quote tags so quote showed up correctly ChrisB
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ChrisB
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Re: Battery Choices

Postby ChrisB » Wed Mar 19, 2008 10:31 am

hyve wrote:.........If though you use ordinary car batteries they can cope fine with this, but won't like the 100 or so amps continuous you'll need to maintain speed thereafter.
This suggests to me that to use lead acid you need a set of each, doubling the awful weight penalty which batteries incur............


As you say Car starter batteries fail due to the fact they are designed to give high outputs for short duration, so you need to look at good capacity cyclic batteries and you will find you may have to over compensate in short term discharge to get the long term discharge correct.

Sort of all to do with C ratings and if my memory serves me correct the purket value ???

The main issue is batteries are happiest when being discharged at a constant rate and within there spec especially PB's, the trouble is an EV discharge is all over the place due to accelleration from stand still, hills, etc etc and a lot of the time you end up exceeding the spec of the battery and hence they fall over quite quickly :cry:
You could of course just bung mahoozive spec'd batteries into the vehicle and then you wouldnt have this problem, but then you'd have a weight issue and so it goes on , so the key is to "try" and match your average discharge the best you can with the weight you have and all the other calcs needed to pick the battery that will do the job :wink:
Tis not that easy.

I've got reams of calcs for forklift battery selection, this is of course one reason why forklifts/milk floats use such massive batteries as they need to opperate for long periods and hence have to carry large cells about, but then they dont need to go so fast and can be geared so they keep out going currents within the spec of the batteries.

Ruddy complicated isnt it :lol:

ChrisB
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aminorjourney
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Postby aminorjourney » Wed Mar 19, 2008 12:58 pm

I have some simple tips I'd like to offer, given a few years worth of daily EV driving:

1) Never scrip on batteries. EVER. Buy the best and most expensive traction batteries you can afford, preferably with a warranty of some description.

2) Buy a decent charger. Charge them using an appropriate charger and carry out regular checks to make sure they're not getting over charged or, in the case of flooded batteries, have enough water in them.

3) Keep your batteries warm and ventilated in winter and cool and ventilated in the summer.. They will perform better (certainly true in my experiences with both lead and lithium batteries) Wrap them up, and use a proper heating and cooling system as well as ventilation system.

4) Buy batteries which will provide you with the range you require plus at least 30%. That way you're not discharging the batteries fully every time you use them and they will (hopefully) last longer.

You can go for cheap batteries but you have to be prepared to deal with the consequences. If you're driving an EV for a hobby vehicle then that's not too bad, but if you're like me and driving an EV daily you need batteries you can rely on and ones which won't require you spend every night or weekend fettling them! :)

Good luck :)

Nikki.

P.S. I switched to Lithium and I'll never switch back to Lead Acid!
Nikki Gordon-Bloomfield

EVangelist and Media Relations Coordinator, www.ZeroCarbonWorld.org
Host, www.transportevolved.com

http://about.me/aminorjourney/bio

hyve
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Choosing batteries

Postby hyve » Fri Mar 21, 2008 9:47 am

Well, these replies seem to confirm what I thought. As Chris B says, ruddy complicated - if you use lead acid anyway. Strikes me there's an opportunity for some software developer to produce a programme to do the calculus required to optimise your choice. I don't do calculus, but I can just about recognise when it is necessary !

Nikki, you're probably right, which I think I've said before.
It seems lead acid cannot really do both jobs well ( heavy draw for acceleration PLUS constant deep cycling) so a modern technology is called for, regardless of cost, almost. Which brings me back to the LiFePO4 batteries. Since my first post I spotted a figure for Thundersky suggesting a 60% better performance for the weight, perhaps because the LiFePO4's have an iron compound in the chemistry ?

But then I spotted on p.25 of the March Battery Vehicle Review an email from nrgcells' John Grzan in Singapore claiming about 250% better performance for batteries made by his firm, http://www.worleyparsons.com/aes. This sounds extremely impressive but after contacting him and getting links to the appropriate web pages, I find I can't open them ! Acrobat says they don't exist.... anyone else looked into this ? A 250% performance upgrade sounds well worth investigating to me.
At present I calculate petrol has about a 100:1 advantage over batteries in terms of energy storage per kg, which is what is really holding the pure electric car back. The extra mass to be hauled about in batteries means extra energy used up, and even if it's used more efficiently, that 100:1 advantage takes a lot of cancelling.
More, while batteries are being charged by power from coal fired generators it is not very green to use extra energy this way. So whatever improvements are made in batteries have to be seized upon, gladly. If the Worley Parsons cells are as claimed, that 100:1 ratio becomes 40:1.

Don't think from the above that I'm knocking electric cars; they're the only way the whole planet can have personal transport. I'm just trying to get a true picture of what we're grappling with.
Peter Ph


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