Solutions to 12 Volt Batteries and Chargers Posted Here

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Any thoughts on getting a 2A or 4A 12V battery maintainer that auto-switches between supply input of 120V or 240V as needed, and splice it into the L1 and L2/N wires, as close as possible to the J1772 socket?

This would provide a charge or maintenance boost as needed to the 12V battery, any time the Leaf is actively charging via the L1 or L2 charger. This should keep the aux battery charged under normal conditions, although there still may be issues with extremely infrequent vehicle use.

The hardest part of the process would be making a clean splice into what is likely 8 (or maybe even 6) gauge stranded wires. The "intelligence" of the charging system is done through the other three connectors in the socket. The L1 wire is always 120V AC, the L2/N is either 120V AC, out of phase with L1, or neutral, depending on what is supplied to the EVSE, and both conductors are disconnected until the vehicle requests charge. And tieing in a device designed to use less than an amp to cables carring up to 30A is safe enough, as long as the connection is properly fused.

Or am I missing something?



grnbrg.
 
The Leaf is already setup to charge the 12v battery whenever a charging session is initiated. If you need additional charging, get one of the low amp maintainers and the separate cable with connector that attaches to the battery. Run the end of the connector into the bay with the J1772 connector. Plug in the maintainer when you plug in the charging cable. Much easier and safer than what you propose.
 
baustin said:
The Leaf is already setup to charge the 12v battery whenever a charging session is initiated.
Yeah, it charges the 12V battery for about 20 seconds (at least on the MY2014s and earlier). Then it goes into float mode at 13.1V for the rest of the charging session (except in low temperatures that you likely never see in Las Vegas).
baustin said:
If you need additional charging, get one of the low amp maintainers and the separate cable with connector that attaches to the battery. Run the end of the connector into the bay with the J1772 connector. Plug in the maintainer when you plug in the charging cable. Much easier and safer than what you propose.
That won't work. The LEAF draws more current from the 12V bus during charging than "one of the low amp maintainers" is capable of putting out. As a result, the 12V battery will be floated at 13.1V just as it normally is.

If you want to use a low-amp maintainer to charge the 12V battery in the Nissan LEAF, use the maintainer when the LEAF's main battery is NOT charging.
 
RegGuheert said:
Yeah, it charges the 12V battery for about 20 seconds (at least on the MY2014s and earlier). Then it goes into float mode at 13.1V for the rest of the charging session (except in low temperatures that you likely never see in Las Vegas)

Please, if you don't like efficiency mode, disconnect current sensor and
battery charging algorithm will stay in "non efficient always excessively charging 14.x V something mode" ;)
That is the only reason why Leaf has a current sensor. Add it to Arnis' DIY mod list :lol:

PS: Yesterday, I had one deeply discharged battery from another ICE. Battery was at 6V for a month. Connected it to Leaf's battery terminals. It took 2-3A for 10-30 minutes and then self-revived to healthy state. Took 50-60A for an hour. Then started to drop again. Leaf kept it at 14.4V for hours and then dropped back to maintenance level of 13.1V something after current dropped to few amps. Leaf's onboard DC-DC apparatus is ideal for lead acid battery charging, not on 2011-12 models as some say.
So disconnect current sensor plug.
Or, if you really want to see current data at LeafSpy, disconnect one of the pins and stick in a fixed resistor to trick charging system thinking battery is cold and needs more zap :)
 
This small thingy right at the negative 12V battery terminal.

Looks like this:
3011764__1_2.jpg


Plug connection might look downward or away from battery, depending on the year AFAIK. Doesn't matter. Few thin wires go to that plug.
 
That one, ok, I disconnected it on mine to see if this helps, I have had 3 dead 12v battery situations in the last two weeks. I believe something is staying on and drawing power, but this should at least help when it is "on" it charges the 12v more. While charging the traction battery the 12v was at 13.1 and disconnecting the shunt meter it went to 13.9v, I will watch it while driving and see where it is then.
 
Hello
I replace 12 v pb with 4x 3.2 V 200 Ah lifepo4 battery in my nissan leaf 2018 40kWh
https://evsvet.eu/download/file.php?id=8239&mode=view
The plan is to use lifepo4 battery to power all 12 V accessories, without help from traction battery while driving and save a kWh .
the contactor disconects the dc/dc when you turn on the car .
everithing works ok exept charging, the dc/dc wants 14.4 V on the battery regardles of the amps, a have seen 130 A.

I replace thick cable from dc/dc to battery with 2 m 10 mm sq , now the amps stay's around 100 A.
is there a better way to limit the current from dc/dc
 
sounds like a lot of work and risk...vs little reward :(

That terminal bar going right above the hold down straps looks down right dangerous :oops:
 
pirpy said:
Hello
I replace 12 v pb with 4x 3.2 V 200 Ah lifepo4 battery in my nissan leaf 2018 40kWh
https://evsvet.eu/download/file.php?id=8239&mode=view
The plan is to use lifepo4 battery to power all 12 V accessories, without help from traction battery while driving and save a kWh .
the contactor disconects the dc/dc when you turn on the car .
everithing works ok exept charging, the dc/dc wants 14.4 V on the battery regardles of the amps, a have seen 130 A.
I had a good laugh when I saw the picture, not in a bad way. You have enough battery capacity to power the car for at least (2.5 x 5) +12 miles or so on just that battery alone. :lol: Kudos for being brave enough to put a battery of that size and capacity in as a replacement.

The Leaf is going to float the battery voltage and draw from the traction battery anyway. I have a bank of similar batteries for my solar, so they work at 12.8 volts with a 14.6 volt max cap, but the Leaf tops out the 12v bus voltage at 14.4, so it will never actually fully charge a lithium battery. It's good in the sense that it maintains long life, I think that is why mine has lasted over 6 years in my Leaf without any noticeable capacity deterioration. That's the reason I think that won't work to save you range, the battery won't be able to hold a high voltage at all times, so the inverter DC to DC is going to do all the work anyway from the traction battery. What that large lithium battery can do is give you a hell-of-a buffer for a 12V DC to 120V AC backup system though, easily run a 1500 watt inverter for home or backup power.

I replace thick cable from dc/dc to battery with 2 m 10 mm sq , now the amps stay's around 100 A.
is there a better way to limit the current from dc/dc
Yes, you need smaller wire actually. To prevent my small Lithium battery in my Leaf from overloading from the 12 volt system, I just used 10 gauge wire for the connections. That naturally limits the current to and from the battery to prevent the DC-DC system from blasting it with over +100 amps of current during the charge cycle and it also limits the output power enough that starting the Leaf or running the Accessories isn't an issue but large current draws from say the inverter system I use for backup power for my home can't pull enough from the battery to harm/overheat it, so the DC-DC system has to make up the difference. It was easier than trying to design a circuit to do all of that in real-time, just have plain ole' physics keep things in check. ;)
 
Hello

The hold down strap has a thick insulation with 2 layers of heatshrink so it should not be a problem.

In between dcdc and battery is a big contactor that disconnects battery and all 12 systems from the dcdc, so no current draw from main battery when car is on (only 200 ohm resistor is permanently bridges dcdc and battery so that there is no error in the dash.
When car is charging the aux socket is off and thus maint contactor is off and through the NC contact of the contactor the dcdc charge the 12 v lifepo4 until the current draw is less than an amp or so and then goes to float mode.
as I said, everything works great except charging, when I connect granny , all the power goes to the 12 V until lifepo4 is nearly full ...
But I had an idea today, I will install big 300 A igbt instead of contactor, the igbt has a natural voltage drop so the lifepo4 wil never be at full charge and I can limit the charging power too with igbt.
It will need a heat sink though.

file.php


Is there a way to put pictures on the forum? links tend to disapear in time
 
I would at least electrical tape the interconnect bars in case something fell across them. Unless you have something else nonconductive that covers the whole thing?

It's funny, I did this with our 2003 VW TDI, disconnected the alternator and had a big battery in the back feeding a big inverter and a 55 amp charger that kept the main battery at 14.4v. If I recall correctly it added about 2 mpg to my overall mpg.
 
pirpy said:
...The hold down strap has a thick insulation with 2 layers of heatshrink so it should not be a problem...

That's a cavalier attitude considering these cells can easily put several thousand amperes into a dead short to ground. I wouldn't stake my bets on shrink wrap abrasian resistance in that configuration. I'd strongly suggest making the upper hold-down strap out of non-conductive material. I'd also cover the entire top to prevent inadvertent shorts from dropped tools, etc.

Further suggestion would be use of flexible, braided bus bars. Solid ones can lever bolts loose in a vibration-heavy application. In addition, use of NordLock bolts and washers for the terminal bolts to keep connections tight. Here's one source for examples: http://store.evtv.me/products.php?cat=7 I used this method for several years with an 8-cell pack in my lawnmower over quite bumpy terrain and never had a problem with loosening.
 
Of course this is a test setup, if sucsesfull I will replace the batteries with newer aluminium type lifepo4, and probably biger capacity.
I use the same type busbars on my tractor, so far so good :)
https://photos.app.goo.gl/xLrRY899GK3R51GK9
https://youtu.be/WkhPTm7eY7Q
https://youtu.be/2PYjlJFJ53Q
 
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