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Discussion Starter #1
Has anyone considered or tried replacing the 12v Battery with a 12v Ultracapacitor? Maxwell makes a version for trucks to assist in cold weather starting scenarios. It seems to me that it would be a fantastic option for EV's. They weigh 1/3 or less than the standard lead/acid battery, provide the same or better cold cranking amps, and last longer. They can also recharge in 15min or less. It seems like it would be a win/win arrangement.

This is the White Sheet for the Maxwell products intended for big trucks:
http://www.maxwell.com/images/documents/ESM_12V_DS_3000552_EN_2.pdf



 

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You don't need high CCA, there is no engine cranking. You do need capacity though, and ultra caps have no where near the capacity of batteries. The larger battery in the reference is 1000 Farads, which seems like a lot, but it's only 20 WHrs at 12V. Or less energy than you probably have in your laptop. I've thought about replacing Volts AGM 12V with a Lithium jump pack (without caps). Would need to work out charging, however. Those jump packs won't like the 15V Volt would provide to it!

We did have someone on this forum that did exactly that (use a 12V jump pack).
 

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You don't need high CCA, there is no engine cranking. You do need capacity though, and ultra caps have no where near the capacity of batteries. The larger battery in the reference is 1000 Farads, which seems like a lot, but it's only 20 WHrs at 12V. Or less energy than you probably have in your laptop. I've thought about replacing Volts AGM 12V with a Lithium jump pack (without caps). Would need to work out charging, however. Those jump packs won't like the 15V Volt would provide to it!

We did have someone on this forum that did exactly that (use a 12V jump pack).
Another forum user has been experimenting with a rechargeable lithium ion battery pack designed for extra charging capacity for phones and tablets. Yet, I'm not one to waver from the manufacturer's design.
 

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Lead acid even AGM = cheap and reliable. Don't mess with it.
 

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What the Volt could use is about 30 of those ultra caps in series tied to the output of the traction battery, to give instant high current burst when the driver hits the accelerator, which would give quicker current flow to the electric motor, and less voltage drop, which would increase acceleration.
 

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What the Volt could use is about 30 of those ultra caps in series tied to the output of the traction battery, to give instant high current burst when the driver hits the accelerator, which would give quicker current flow to the electric motor, and less voltage drop, which would increase acceleration.
Skip the ultracapacitor and just install a flux capacitor!!!
 

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Bad idea, it slowly self discharges and will brick your car due to lack of capacity
 

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What the Volt could use is about 30 of those ultra caps in series tied to the output of the traction battery, to give instant high current burst when the driver hits the accelerator, which would give quicker current flow to the electric motor, and less voltage drop, which would increase acceleration.
My understanding is that EVs have the opposite issue - too much acceleration. Thus the engineers figure out ways to dial back the amount of energy that can be sent to the drive motors at any given time.
 

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Discussion Starter #9
My understanding is that the battery is charging every time the car is turned on. The battery doesn't need much capacity. It just needs to start the motor...usually while the car is already on and moving. So the capacitor would be charged, the motor would start, then nearly instantly the capacitor would be charged again. The rest of the time it's mostly dead weight except for powering the accessories in the car, but that isn't really an issue because the power comes from the traction battery to the capacitor which can accept the charge WAY faster than a lead/acid battery. I realize that it isn't cost effective, but I think it would work, and work well. If all the EVs changed strategy, it would come down in price.
 

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Has anyone considered or tried replacing the 12v Battery with a 12v Ultracapacitor? Maxwell makes a version for trucks to assist in cold weather starting scenarios. It seems to me that it would be a fantastic option for EV's. They weigh 1/3 or less than the standard lead/acid battery, provide the same or better cold cranking amps, and last longer. They can also recharge in 15min or less. It seems like it would be a win/win arrangement.
I did some digging. It's apparently NOT a drop-in replacement for a 12v. There's installation involved. And the installed price is $1400. I have a tough time imagining what kind of advantages I'd see that are worth more than five times the price. At least not in car that isn't burning up a battery a year because it's starting an ICE 100 times a day.
 

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Discussion Starter #11
The item I linked to wouldn't work in the Volt. It would need to be something smaller.


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I had a long talk with Tony Williams last year at the Cupertino Drive Electric event. He had been experimenting at one point with a "drop-in" Lithium 12v battery. The one he was using was the Valence U1-12RT: https://www.valence.com/products/standard-modules/rt-modules/ It is a Li iron phosphate battery, and has a built-in management system to ensure proper charging and such. There was a guy with a RAV4 EV parked next to Tonys booth that had one. He mentioned some issues with it, but I don't recall what they were. (Perhaps the same as mentioned here: http://www.myrav4ev.com/forum/viewtopic.php?f=9&t=1617)
 

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Discussion Starter #14
I had a long talk with Tony Williams last year at the Cupertino Drive Electric event. He had been experimenting at one point with a "drop-in" Lithium 12v battery. The one he was using was the Valence U1-12RT: https://www.valence.com/products/standard-modules/rt-modules/ It is a Li iron phosphate battery, and has a built-in management system to ensure proper charging and such. There was a guy with a RAV4 EV parked next to Tonys booth that had one. He mentioned some issues with it, but I don't recall what they were. (Perhaps the same as mentioned here: http://www.myrav4ev.com/forum/viewtopic.php?f=9&t=1617)
The guy who runs the lasersaber YouTube channel built a LiFe Phosphate battery coupled with a ultracapacitor boostpack that he used for several years to start his car. Originally he was using just the capacitors, but he added the battery because of the loss of charge over just a few days. I just think that something could be built and used that is MUCH lighter than a giant standard 12v battery. That's a huge amount of dead weight to haul around for the minimal demands that are placed on it.
 

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Lead acid even AGM = cheap and reliable. Don't mess with it.
Reliable? Yes!
Cheap? No! Well, compared to this capacitor, you're right. Compared to normal lead-acid, it's like double the price, unfortunately.

obermd said:
My understanding is that EVs have the opposite issue - too much acceleration. Thus the engineers figure out ways to dial back the amount of energy that can be sent to the drive motors at any given time.
It's really that electric motors have full torque at near 0 rpm, which can be a shock to the drivetrain. So they "soft start" them a bit. Nothing to really do with the battery, it's a characteristic of motors.

Capacitors could be used to allow a PHEV with a small pack to have better acceleration. Something with a 3kWh pack won't normally be able to provide a lot of power due to small capacity. The capacitors could be placed in parallel with the pack to provide extra current during acceleration, more than the smaller pack could normally handle (it acts like a buffer). But ones that could hold the energy required would probably be too expensive.

Ztirffritz said:
My understanding is that the battery is charging every time the car is turned on. The battery doesn't need much capacity. It just needs to start the motor...usually while the car is already on and moving. So the capacitor would be charged, the motor would start, then nearly instantly the capacitor would be charged again. The rest of the time it's mostly dead weight except for powering the accessories in the car, but that isn't really an issue because the power comes from the traction battery to the capacitor which can accept the charge WAY faster than a lead/acid battery. I realize that it isn't cost effective, but I think it would work, and work well. If all the EVs changed strategy, it would come down in price.
The 12V doesn't even start the motor in a Volt, the traction battery does. The 12V just "boots" the car, turning on computers and connecting traction battery. The 12V battery (or cap) would be charged when the car is on, but that doesn't mean it would work. The battery is a buffer for loads on the 12V system (wipers, lights, radio, steering, etc)... even though the APM provides most of the power, the battery must be able to absorb some decent loads in certain circumstances. It seems like a cap would work, but I doubt it would. The user here who experimented with a small jump-pack eventually was unable to start his car... something during use drained it too low, even though it seems like it should be able to handle it. If that didn't work, the ultra cap wouldn't either. Perhaps a system redesign would make it all work, but the cost of this cap makes it not worth it. Maybe someday when the cost is much lower and energy storage higher...
 

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The 12V doesn't even start the motor in a Volt, the traction battery does. The 12V just "boots" the car, turning on computers and connecting traction battery.
I think (on the gen 1 anyway) that the AGM battery is also what gives you pretty much everything that stays on when you turn the car off, but sit there with the radio et-al on, or need to roll up your windows.

Depending on circumstances that can be a fair bit of draw.
 

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I think (on the gen 1 anyway) that the AGM battery is also what gives you pretty much everything that stays on when you turn the car off, but sit there with the radio et-al on, or need to roll up your windows.

Depending on circumstances that can be a fair bit of draw.

This is true unless you happen to plug in your EVSE since when actively charging the Lear 3.3kW high voltage battery charger in the Volt supplies @14VDC to the AGM battery to keep it topped off. When the Volt has completed charging or you disconnect the EVSE, voltage on the B+ of the AGM returns to the normal @12VDC...
 

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Batteries, Capacitors and Ultra-Caps are a part of any electrical design tradeoff. Like I said in post #2, ultra caps are not suitable to replace the 12V AGM. Yes, it will work, as long as you don't leave the Volt off too long. Yes, they recharge. But there is no benefit. Volt goes to a low power state when off, but there ARE computers running. You can communicate with the car by OnStar. By remote Fob. It uses power. Ultra caps will discharge over time with No load. They'll discharge even faster in a Volt. The 1000F unit shown is 20WHr. You can only use about 30-40% of its energy before the voltage drops too low. Volts AGM is about 720WHr (60AHr*12V). You can use over 50% of it's energy, before recharge. 50X more usable capacity for AGM at a fraction of the cost. The Volt AGM application needs a store of energy capacity, not burst current. With sufficient engineering, Lithium will replace the AGM technology as it gets cheaper and more standardized.
 

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I had my track car ('92 Nissan 240SX - HEAVILY modified, about 2400 lbs, over 500 rwhp out of a turbo 2L) running on a Maxwell 6x 350F ultra cap setup with a 4.2 Ahr LiFePO4 12V battery. The problem is that the LiFePO4 battery does not like to get hit with a full 14.4V after it's been pulled down on a start - especially on a cold day. So you really need to protect it with a current limiting resistor to buffer it from charging current, which limits how many amps it will provide on peak. The ultracaps can deliver a ton of current, but have very little capacity. My pack would be pulled down to <10 V after ~2-3 revolutions of the 4 cylinder engine, which would let it start with a factory ECU, but the aftermarket ECU needed that much just to sync up timing, then it wouldn't have enough left to start it. The battery provided just enough current to get things started on a warmish day, but around freezing it'd really struggle and I'd have to "prime" the battery with a start attempt or two. I had to disconnect the battery via a circuit breaker when the car sat for any length of time, as it only had about 3 Ahr of capacity before it couldn't start the engine.

All of the above setup is good for peak current delivery but has low power capacity. Given the Volt doesn't need peak current delivery, but does need high power capacity - it just wouldn't work. You'd probably draw down a reasonable set of ultracaps in a day or less in a car that's locked up and drawing <20 mA. If the interior lights come on, you'd probably kill it in a couple of minutes max.

A bigger LiFePO4 battery could work, but honestly, I'd be worried about hitting it with way too much charging current. Plus to get ~15-20 Ahr of capacity at 12 V with LiFePO4 is kinda pricey. You're probably about 2-3x high quality AGM batteries in cost at that point, even trying to play it cheap. If you go "premade" on everything, you're probably at 5-6x AGM pricing. It won't last 5-6x longer than an AGM battery in this usage scenario either...

At the end of the day, the AGM battery is probably the cheapest way to provide 12V power in the Volt over a given time period.
 

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It's not broken. Don't fix it.

One of the major problems with lithium for a 12V system is that lithium cannot be safely charged below certain temperatures. Around 45F, you start getting lithium plating at high charge rates, and you simply can't safely charge lithium much below 20F without getting plating, which is permanent capacity loss. Not ideal.

Lead acid is often seen as an inferior battery, but for automotive systems, it's good enough, and everything is designed around the voltage ranges it operates at. It works (without being damaged) in all temperatures without thermal regulation (you may have problems if you deeply discharge one well below 0F - they can freeze at some point), it's cheap, it's commonly recycled, and for what they're asked to do, there's no reason to replace it with something different.

The Volt AGM, as has been noted, is not doing "starting duty" - it's simply running the computers, lights, windows, and other ancillary systems.

Ultra-capacitors, without some sort of boost converter, are especially inefficient, because you can't even use their whole voltage range. A lead acid based system operates between 10V and 15V (give or take - you shouldn't be at either extreme, but things more or less work in that range), but to get the full rated capacity out of an ultracapacitor, you'd need to drop to 0V - which a typical system won't do. So you'd need a boost converter. And then it would have to handle limiting charging current. It's simply more complexity than it's worth.

Given that the Volt chews through 12V batteries, it might be worth wiring a battery tender in such that whenever the shore power is connected, the 12V battery is getting charged. I believe it only charges when the main HV battery is charging, instead of always using the shore power - and that's hard on a 12V lead acid battery. I may mess with this at some point.
 
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