[TrevorH]

I was wondering whether anyone has added an additional battery pack in parallel to the standard cell to extend range under "electric motor only" motoring?

 

[john1701a]

Yes, a few have. And it has worked extremely well.

Prius is so remarkably well thought out that a few have actually been converted to fuel-cell vehicles too, taking full advantge of the electric platform readily available.

 

[TrevorH]

Hi John

Thanks for the reply. I was wondering if you knew any websites where the additional cell concept has been detailed from a technical point of view. I figure that the battery management ECU could get confused by the additional cell given the readings it takes from the original cell to manage charging. My thought was to charge the additional cell from the grid and then connect it to the primary for travel. Any other thoughts.

Trevor

 

[frenchie]

Prius is so remarkably well thought out that a few have actually been converted to fuel-cell vehicles too

Are you sure John ? I've read about hydrogen Priuses, but they were not fuel cell cars, they just used a modified engine with a turbocharger. And that was pure nonsense to me, since the resulting car is not only more expensive and less practical (huge hydrogen tank in the trunk, ridiculous autonomy!), but much less efficient than the original Prius (making and storing hydrogen costs a lot of energy).

 

[john1701a]

Yes, I am sure... 2 types.

There are some that simply just burn hydrogen in the engine instead of gas. And others that don't have an engine at all, instead a fuel-cell providing electricity.

 

[clett]

Hi Trevor,

Sounds like a great idea to me, and if you could demonstrate a 20 mile plug-in range Prius, I'm pretty sure Toyota would also be really keen to see that working (and maybe give them some good ideas for Prius 3, hint hint!). Wouldn't it be great if the first plug-in hybrids on the road were amateur conversions like this?

Anyway, as for battery options you have several:

1) NiMH
You could simply put in parallel an extra NiMH pack of the same type already used in your 2004. They are made by Panasonic EV (see here), and have about 46Wh/kg, but given the huge demand for them right now (not just for Prius, but all the other coming hybrids), the chance of a private individual like yourself managing to buy one either from them or from your local Toyota parts department is probably next to negligible right now!
Alternatively, you could maybe buy some of the packs they made for the RAV4 EV. THey're designed for much deeper charge/discharge cycles, and at 65Wh/kg would be much better for range extending purposes. As the RAV4 EV has been canned, they might even be available too, though they will be expensive.

2) Lead acid
Don't do it! 35Wh/kg at best would mean a very heavy Prius for a very modest range (figure on about 4 miles range per kWh storage).

3) Thundersky Lithium Ion
Now we're talking! 140Wh/kg, readily available to the amateur (see here) at about $200 per kWh. A 50 kilo pack in the boot wouldn't take up too much space, and with 7kWh would give you a plug-in-electric range of about 28 miles - enough for many people's commutes.

4) 18650 Lithium Ion
Or, for the same numbers, you could try taking the 18650 route. These are the small cylindrical ~AA sized batteries used to make up camera and laptop batteries. (Roughly on a par with the thundersky on cost, off the shelf availability and energy density). The only difference is that these would be more fiddly to use. The 28 mile EV range would require you to build a pack made up of about 1,200 individual cells, just as AC propulsion have done to such great effect!

5) Lithium Sulphur
OK, so you can't buy these just yet! But with 350Wh/kg storage already demonstrated by SION for laptop batteries, a 100kg LiS battery in the boot would give you an all electric range of up to 140 miles before the ICE engine even needs to start up. Come on Toyota, drop this fuel cell crap and DO A DEAL WITH SION!!!!

 

[richard schumacher]

Don't overlook the interim possibility of using a closed-cycle fuel cell as a battery replacement. It would cost more to install and the specific energy density is probably not great but the net efficiency could be more than 60% (versus about 30% for a battery system) and it would be capable of very high charge and discharge rates.

 

[BIF]

...
5) Lithium Sulphur
OK, so you can't buy these just yet! But with 350Wh/kg storage already demonstrated by SION for laptop batteries, a 100kg LiS battery in the boot would give you an all electric range of up to 140 miles before the ICE engine even needs to start up. Come on Toyota, drop this fuel cell crap and DO A DEAL WITH SION!!!!

Nice, however, if you read the article more closely, you'll see that SION claims that you can get > 300 recharge cycles. I'm sorry, but even if they're really being conservative in their estimates, and are understating the expections by a full 50%, it's still not good enough, nor sustainable enough for automotive use, because you'd be replacing the battery once or twice each year, depending on the accuracy of their estimate and your frequency of use.

 

[clett]

Don't overlook the interim possibility of using a closed-cycle fuel cell as a battery replacement. It would cost more to install and the specific energy density is probably not great but the net efficiency could be more than 60% (versus about 30% for a battery system) and it would be capable of very high charge and discharge rates.

There is no way that a fuel cell can ever compete with a battery on efficiency terms! At peak efficiency a PEM fuel cell can only manage about 50% efficiency. And in terms of regen, the one thing fuel cells don't like is being started and stopped quickly (power must be ramped up slowly - in or out), so a battery (or even better an ultracap) will always be better for this function. Where did you get the 30% figure for battery-electric efficiency from? It's more like mid-nineties for LiIon, and a large battery (such as the one suggested) will always be much better than a small one at capturing regen energy (simply because it can handle higher power inputs). A similar subject was debated recently over here if you're interested.

 

[clett]

Nice, however, if you read the article more closely, you'll see that SION claims that you can get > 300 recharge cycles. I'm sorry, but even if they're really being conservative in their estimates, and are understating the expections by a full 50%, it's still not good enough, nor sustainable enough for automotive use, because you'd be replacing the battery once or twice each year, depending on the accuracy of their estimate and your frequency of use.

You're right, the cycle life thing is a big issue yet to be properly resolved for LiS. In fact it's the main reason why they're still at the research and development stage and not on the shelves yet (I think the aim is 1,000 cycles).

However, people rarely completely discharge EV batteries, and with shallower cycles than 100%-0%, cycle lives are always much longer (hence the reason Toyota only allow a 80%-40% discharge in the Prius - ie it greatly improves longevity). And even when the battery gets to the end of it's most efficient design life (let's say 300 cycles at the moment, so maybe at 42,000 miles or 3-4 years), the battery doesn't just die, it just holds less and less charge. Make no mistake though, improvements are yet to come in this technology which is at present only in it's infancy. You heard it here first! :wink:

 

[richard schumacher]

Where did you get the 30% figure for battery-electric efficiency from? It's more like mid-nineties for LiIon, and a large battery (such as the one suggested) will always be much better than a small one at capturing regen energy (simply because it can handle higher power inputs). A similar subject was debated recently over here if you're interested.

I guess I was mistaken about the utility of a fuel cell for energy storage.

Can you cite a source for that mid-nineties figure for LiIon batteries?

 

[BIF]

Clett:

Yes, new developments are always happening. I will keep this in mind. I'm hoping for a usable life of 5 to 8 years or longer...so it's got to be able to handle thousands (plural) of charge/discharge cycles, similar to the current NiMH batteries. Anything less would be unacceptable, from any type of cost/practicatlity/manufacturing/waste standpoint.

It would be nice to have the unit easily able to connect/disconnect, so that if you need more room for carrying something, you can just deinstall it quickly, and reinstall it later.

 

[clett]

Can you cite a source for that mid-nineties figure for LiIon batteries?

Sure, found these two pages that put it at around 99% efficiency in terms of what you get out compared to what you put in for LiIon if they aren't charged too rapidly.

 

[richard schumacher]

Sure, found these two pages that put it at around 99% efficiency in terms of what you get out compared to what you put in for LiIon if they aren't charged too rapidly.

Remarkable. Apparently the only limiters of the efficiency are the charge and discharge rates?