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Old 08-13-2015, 01:32 AM   #1 (permalink)
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New lighter 12v battery option that looks promising.

Saw this today its a new 6lb 12 volt car battery that you can use in nearly any car. It looks promising and should be a great alternative to someone who wants to save weight but whats to keep the oem look and is not a major DIYer. If figure if anyone would appreciate this, it would be us EcoModders

Ohm Is A Smarter, Lighter Car Battery That Works With Your Existing Car | TechCrunch

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Old 08-13-2015, 11:53 PM   #2 (permalink)
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I already did this about 2 years ago. Replaced 2 batteries weighing up to 120 pounds with a 25 to 30 pound LiFePO4.

Ok so this "Ohm battery" appears to be super capacitor boosted LiFePO4 technology.
The LiFePO4 I have been there. Done that.
Adding the super caps to the LiFePO4 is the next logical step.

I will lend you my observations and experiences on this subject of swapping from lead acid tech to lithium.
LiFePO4 is the best, safest, cheapest option for a straight drop in replacement for lead acid tech.

First and most importantly, what I did not know, or may not have been widely known when I built my LiFePO4 batteries:
Charging them when their temperature is below 5'C will permanently damage them.

Second most important thing, with out the super caps the lithium's amp out put drops like a lift with its cable cut as the battery temperature gets close to and drops below freezing.

Also, LiFePO4 batteries do not like excessive heat. Under the hood of your car, not really the best place for it. I would highly recommend a battery relocation to a place that has a more stabile temperature.

When a LiFePO4 battery gets discharged, they become very power hungry due to low internal resistance. It puts a lot of load on the alternator after initial start up, enough so to the point where I have considered installing a charge limiting resistor for use after initial startup to make life on the alternator a little easier and to reduce belt squeal.

But once the LiFePO4 batteries get 14.4 volts they draw almost no power. A large flooded lead acid truck battery will consume up to about 2 amps just to maintain the voltage at 14.4V. Once the LiFePO4 batteries get up to 14.4V they draw almost no amps.
Once LiFePO4 batteries are up to voltage they are fully charged. Lead acid requires some absorption time. For heavy duty, real deep cycle batteries found in forklift traction and off grid power applications this absorption cycle should last 3 to 4 hours at 2.4 volts per cell (14.4 for a standard 12 volt battery), this also varies with temperature.
Lead acid starting batteries are designed to charge, discharge real fast, so they do not need a 3 to 4 hour absorption cycle, but you get the idea.

The article claims up to a 7 year life. Yes I could see that. By now, if I had not built my LiFePO4 batteries I would have put more lead acids in and likely replaced them.
This battery has a discharge preventer, that is good. You want that because if you kill LiFePO4 batteries, they are likely going to be done.

As far as I am concerned lead acid only has 3 advantages over lithium.
The lead acid battery is likely the most recycled consumer item on earth.
Lithium batteries are currently not recycled.
Lead tech is proven in cold weather.
Flooded lead acids are initially cheaper.
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Old 08-14-2015, 06:20 AM   #3 (permalink)
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I fitted a LiFe battery to UFI, I found that the high parasitic draw of a modern car will kill a LiFe battery very quickly if you're not careful (due to relatively low reserve capacity - I had 14Ah). Many new cars with electric everything are lucky to get three years out of a lead acid battery, my Pb battery only lasted about nine months from new, and the LiFe only went two tanks

LiFe batteries can also cause new cars to have electical gremlins due to the change in voltage, charge acceptance etc. My car had all sorts of issues and I finally resigned myself to the old Pb tech.

Even fitting a Supercap to the Pb battery on my low tech Renault caused issue.
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Old 08-14-2015, 08:40 AM   #4 (permalink)
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I'm building a parallel high voltage hybrid pack for my Insight, and if that is either working well or failed so I can reuse the cells, I would like to replace the ailing 12V lead battery.

I would use a top balancing BMS, of course. But I would also add a big diode and a NTC regulated charge limiter; the colder, the lower the charging current would be.

Finally I would indeed place the battery as low as possible, preferably at the bottom of a deep watertight box to protect it from splashes and flooding, with terminals on the top of it (at the same level as the current battery top).

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