The title is most of the question,
Nissan Leaf batteries are 7.x volt lithium ion so running a pair of them in series gets you just about 16v. I want to run these in a 12v automotive system and I am having trouble finding out if there is any potential harm from running the slightly higher voltage and wondering if they will even charge to the 16v level off the cars 15v charging system?
You want to run these modules as a direct car battery replacement?
Aside from all the issues with regulation, the voltage is too low. According to this link (which is also consistent with what I know of lithium ion), 90% of the capacity is in the range of 3.65-4.2 volts per cell. The bottom range of that, times 4 cells, is 14.6 v. That’s already over the standard 14.5 v regulation limit of a car alternator, so at best you’ll have 10% remaining capacity from the packs.
There are all kinds of other issues with ensuring there are no voltage spikes in the system, and that you don’t charge at too high a rate (most auto systems don’t have any current regulation at all), and so on. So this seems like a bad idea.
From that link
So the module is 7.6v, 2 of those in series would be 15.2v max. my alternator and my battery charger both charge at 15v.
I missed the edit window, that page has good info but you are reading it wrong,
so the 2 cells in the unit add up to 7.6v
with 2 units you get 15.2v hooked up in series.
the under lined bit is my concern. at max a pair of these would be 16.8v which is a bit outside the 15v my charging system is currently putting out with no harm to the overall electrical system in the vehicle.
the goal here is to use these as power storage for interior lights, and other electrical needs in an RV. They would eventually be tied to the alternator, the generator, and to solar panels.
do not use lithium ion batteries in this way unless you’re OK with them overheating and catching fire or exploding. Automotive 12 volt systems use lead-acid batteries because they tolerate being charged using constant voltage and tolerate being held above their full-charge voltage for extended lengths of time. Lithium ion cells are very, very intolerant of misuse which is why they need their own specific chargers.
I’m not sure if automotive lithium ion batteries use the same algorithm, but smaller lithium ion batteries don’t use a constant voltage for charging. You charge first with a constant current until the voltage reaches close to full charge. From there, you charge at a constant voltage until the current drops off to almost nothing (the charger generally stops at a specific value like 3 percent of current).
The charging system of an automobile is designed around the lead-acid battery. It is charged with an alternator, which on average puts out something above 12 volts (typically in the 14 to 15 volt range) but it’s nowhere near a constant voltage. Lead-acid batteries handle that just fine. That’s not going to work so well for a lithium-ion battery though.
What jz78817 said is also worth repeating. Lithium-ion batteries are generally controlled by some very specific circuitry. Without that circuitry, a fire or an explosion is very likely.
Get yourself some lead-acid batteries. You may need to get a stronger alternator, and make sure you get a generator big enough to handle the extra load as well.
Or alternatively get the correct charging system? These things are a dramatic improvement over lead acid in almost every imaginable way. In addition the Leaf batteries are used in solar systems in the after market on a regular basis so there has to be a way to correctly charge these things.
FWIW what I meant was that automotive charging systems don’t provide a constant-current charge mode to their lead-acid storage batteries. The battery sees whatever voltage the alternator is providing regardless of its state of charge.
Yeah, I knew what you meant. I wasn’t nitpicking your post, I was just explaining why it wouldn’t work for lithium-ion.
I don’t think so.
7.6 v is the “nominal” voltage. It’s basically the average voltage across the full state of charge, not a maximum or minimum.
8.4 v is the maximum voltage. This is the fully charged state.
7.3 v is effectively depleted: only 10% of the capacity is left at that voltage. If you want the batteries to be useful at all, you need to charge well above this voltage. 8.4 v ideally, but somewhere around 7.8 v would be reasonable.
But to repeat what I and others said, you need some form of current regulation, and ideally some better voltage protection than what the alternator has built in. Lithium-ion is a whole different beast than lead-acid and is far less tolerant of abuse.
Also, just putting two packs in series will lead to problems. You need a means of balancing the pack voltages. The packs may or may not have this built in, but regardless you need some balancing between packs.
Well, as usual you guys rock. thanks for the input. I will start looking at charge controllers and the like.
Ignore the people saying the Li-Ion can’t take the charge rate. That all depends on the surface area. But surface area equally affects current output capability too.
Basically, if its going to produce 50 Amps, its going to be able to charge at 50 Amps, right ?
Here’s a discussion of how to manage automotive Li Ion batt charging.
http://victoriaevclub.com/forum/victoria-bc/healthy-battery-practices/
Basically, you want to mentally decide whether to charge to 40% , for just driving, OR to a higher %, for use as a supply of 12 volts power. (eg to run peltier cooler, TV, computer,etc,whether by inverter or not.)
So here’s a discussion of how to get the automotive “alternator” to charge the higher voltage.
http://www.smartgauge.co.uk/alt_mod.html
Its a simple failsafe adaption to approx 5 Amp circuit of the alternator. It points out that you could switch off the alternator , by disconnecting the said diodes. Then you can switch it back on with a different number of diodes, and therefore get its voltage adjusted to suit.
Basically you’d install a rotary dial, which had positions of
zero - OFF, no connection.
- lead acid voltage, wire and no additional diode… or 10% Li-ION
- One diode… 40 % Li-ION. you use this if you are just driving around, as you are not doing charge,discharge cycles , as a single start is barely nothing of the charge… So you are storing the battery when just driving around
- two diodes. 100%
- three diodes. extreme charging
It would be absolutely safe for the battery to install one 0.6 v diode and run around with the Li Ion at 40% all the time
Install a voltage guage so that you can know whether you are at the 80% you want for just a picnic, (benefit, you get longer life from the batts ) or the 100% you want for a full day outing (you reduce the life of the batt by a few days each time.)
NO !.
Ideal is for long life, which means charge it to storage , which is around 40%. there’s no hard cutoffs, its an average, around there, who can say for sure type thing.
Misuse is draining them faster than their design output…
eg short circuiting
Now he’s using a batt from an electric car, which can output 20 kW… So … his charging and discharging would be at 1 kW … how is that EVER going to constitute “misuse” ??
You are quiet about the need for circuitry, but what ? There’s a lot of talk about how the car definitely charges at a constant voltage. Oh no it doesn’t. It has a simple feed back circuit to smoothly drop charging current as the voltage approaches fully charged. So that it doesn’t overshoot. The regulator has the charging voltage built in… thats why the leaf batt can’t go straight into the place of a lead acid.
You mixed up the idea of charging an electric car’s battery with the idea of charging a little tiny RC car Li Ion batt direct from the road vehicle circuit ??
Who says that the OP cares more about long life than capacity? Throwing away 60% of the total capacity is silly.
Also, ~40% is only optimal for long-term storage. If the OP cares more about extracting a certain number of joules from the battery, somewhere around 80% is optimal. A lower depth-of-discharge gives you more cycles, but fewer joules per cycle, and so you end up worse off. A higher depth-of-discharge degrades the battery faster than the extra joules you get, so you again end up worse off.
Temperature is a significant factor. One reason the Leaf batteries degrade faster than (say) Tesla is because they use passive cooling instead of active (liquid) cooling.
Wrong. Lithium-ion cells are generally rated at a much higher discharge rate than charge rate.
Even Tesla’s supercharger doesn’t exceed a 1.4C charge rate. That’s with active cooling, a different cell chemistry, and furthermore they don’t charge at that rate for the entire state of charge range.
The normal charge rate for the Leaf is 1/3C. That’s only 19 A. Even the flimsiest alternators are rated for more than that.
if you don’t know, then you shouldn’t be handing out advice.