# What is an ideal PCB for 2 Nissan Leaf battery modules in series?



## dcb (Dec 5, 2009)

What does PCB mean in your vernacular? You don't need much for 30A, I have two in series on my recumbent (maybe 25 amps, little motor) and I just have a bit of bare copper wire connecting them, clamped under the bolts.


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## TomWaitsman (Oct 12, 2016)

I use PCB/PCM somewhat interchangeably when describing a battery management system. But PCB/PCM are just shorthand for "protection circuit module" or "protection circuit board". I want to integrate one because this battery isn't exactly for an electric bicycle; I need some sort of charge controller and a lot of capacity for the application, which is why I went with the leaf modules.


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## onegreenev (May 18, 2012)

What is your application? Electric Vehicle or Battery Backup? Or Powering your RV? You will need a way to cut off power when your cells reach a specific voltage both on the top and bottom of your desired range. You will need to balance the modules which is rather easy and they are quality enough that they should be real close in capacity so you should not have any issues with grossly out of balance modules. You mention charge controller so Im going to assume here you are considering Solar Battery Backup. Yes?


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## TomWaitsman (Oct 12, 2016)

This battery is being implemented on a coffee service trailer, which can be hitched to any sturdy bicycle. We will also be implementing solar PV as a means to trickle-charge the battery. So I'm trying to build a battery protection circuit that will stop the PV system from overcharging the battery, balance the cells, and redirect current directly to the appliances when the battery is full. I haven't tackled that last bit yet, but I know there are systems out there which do that. 

I was also hoping to buy used cells (this project is very constrained by the budget); do you think I'll run into issues there with out-of-balance modules? I figure that as long as they came from the same car they'll be close enough.


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## dcb (Dec 5, 2009)

ah, ok. PCB means Printed Circuit Board usually. I think the acronym you want is BMS (Battery Management System), which itself can be a little nebulous (some just monitor and alert, some override charge, some override discharge, some both, some have temperature monitoring, coulomb counting, etc. etc.)

Usually "budget" means you trade lots of your own time for some cost savings, but you usually get a bit educated in the process (and occasionally see some cost savings, moreso the more educated you get about a subject).

it is just 4s (4 cells in series) though, so if you source 4 4v adapters (electrically isolated) that will charge it balanced (I just have a 16v laptop adapter on my bike, but I monitor the voltage at various points). And a way to stop discharge when the pack is below say 13 volts. But even that isn't completely "idiotproof", but nothing is really. 

The most budgety thing you can do is what I did, just hook them up, probe all cells occasionally with cheap multimeter and monitor pack voltage while operating it so you don't over-discharge, and use a $5 16v laptop adapter to charge, and manually correct any out of balance, or take other action as appropriate. But it sounds like you want to sell something with batteries in it, instead of for personal use. I don't recommend doing that without educating yourself more about the hazards (they do occasionally catch on fire, even with a production grade BMS).


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## TomWaitsman (Oct 12, 2016)

I admire the simplicity of the laptop charger. The battery is being dropped into a beta prototype, and the most action it will see is probably just some testing and refinement. We're managing risk best we can; last thing anyone needs is a Galaxy S7-type failure. Thanks for the advice!


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## Evilsizer (Jan 25, 2010)

some blanks need to be fillled in, the devices for you coffee cart are AC or DC voltage?

assuming they are ac though i dont know any devices for coffee that are dc other then cheap on the road coffee makers. a bit more info can really help with figuring things out. as right now just assuming they are ac i would suggest a UPS that is "always ON". you could then get solar panels with micro ac inverters attached to them to connect to the UPS. as the always on inverter would have pretty much everything you need for BMS/battery monitor.


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## TomWaitsman (Oct 12, 2016)

Thanks to the aeropress, only a coffee grinder and immersion heater are needed. The coffee grinder is rated for 100 Watts, and will only be turned on for short periods of time. A 12VDC immersion heater will bring water up to brewing temperature when needed. So I figured a 12V 20A voltage regulator on the battery output and a 150W inverter would do the trick. Heating is expected to take up 1.15kWh on a cool overcast day, and grinding 0.21 kWh. The battery may not have enough juice for full day of autonomy, but thats ok. That bit about the inverter acting as a BMS intrigues me. Maybe it would be wise to switch over to all AC power and have it double as a BMS...


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## Evilsizer (Jan 25, 2010)

i would say figure for a worst case scenario of how much power you need for the day, then figure in at least another 15% on top of that. to figure out how much power your going to need, with the 15% buffer as a min. to account for loses with DC->AC->DC->AC conversion. if you dont use a usp but some kind of battery setup with a inverter, got with a puresine wave inverter vs modified sine wave. i forget where i read it but electronic devices like motors be it blender and some other types are more efficient at use the power they get vs what they get with a modified sine wave inverter. 

i did some install work a few years back for a security company. they had a customer request battery backups and what fit for their needs were always on ups's. this way the setup that needed to be on the ups always stayed on and never had any power "hiccups" waiting for the ups to switch over to the battery backup. i forget the size of the ups but the guy at work sized it to where they had a little over 24hrs of run time before they system went down. it just so happened about 2wks after the install of the ups, they had a bad storm. they lost power but everything that needed to run was still going till about 1pm the next day. that is when certain devices stopped working, so even so they had power back to the place. the breakers were still tripped to the ups was not getting power to charge the batteries. they had no clue anything was wrong will things slowly stopped working.

i guess with my last few posts, is that their other devices you can use. that are used for other things that fit what you want. maybe less of a hassle and possibly cheaper for you vs using something like hybrid battery packs and figuring out wiring and bms as well as other things.


keep us posted! im interested to see how this turns out!


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## onegreenev (May 18, 2012)

You need a portable solution. UPS systems require you to be connected to an AC Grid system to work properly. If you will be having direct access to AC power then a small UPS might work. I was thinking you want to use a portable battery that will provide you with all day or how ever long you plan on serving coffee so you never run out of power. A solar trickle will be helpful but only on sunny days. Even with that you will get little benefit but it will be cool to have the cover a solar panel or two. You will need to build your battery pack large enough to last long enough plus some extra time. Batteries degrade with time and use and over time and use you will still want that pack to provide you with what you need. The coffee grinder may not take much power but that immersion heater will surly suck those batteries dry in no time if you are busy and only have a small pack. Thats the other thing. What if you are busy and you did not have a pack large enough to cover that extra load of coffee to make? Plan for it. It may not happen but you need to know it could happen. 

How big should the pack be? Well you could do some math and figure out what each device really does pull during use and then calculate how many times you will do that in a given day. When you get home plug in your cart like we do with our cars. Its the same thing except you are not powering a motor but you are powering electrical devices. The batteries don't know if its a motor or coffee pot. 

Cold weather has an effect on batteries daily capacity too. Plan on that when its cold out.


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## dcb (Dec 5, 2009)

also, you can store energy in the form of heat in the water tank, if it is very well insulated, i.e. have the charger supply enough power to run the heater overnight as well, or more simply just have a 120v element and a 12v element and "charge" it overnight as well.

if you can avoid going to AC then do so, no reason to be wasteful, keep the on the road equipment at the 12v level.

but also water is heavy, so a couple extra batteries might not make a big difference if you have to carry all the water with you.

If it were me, I would figure out how much water I need, get/fabricate/cobble an insulated tank for it, and get an idea how much energy it takes to keep it hot by running the heater, monitoring temps, and seeing the power usage over time (and at worst case outside temperature)


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## TomWaitsman (Oct 12, 2016)

In case anyone still has this thread on their radar, I just wanted to say thanks again for your input and give a little update. This project was my capstone for an engineering degree; in the departments end-of-year showcase, an annual event of 300+ students, parents, etc, this project took home the "peoples choice award" for best concept. 

I ended up buying this

```
http://www.ebay.com/itm/252324044882?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
```
 BMS which arrived slightly broken, but we were able to fix it. The battery and BMS went into a NEMA 3R rated box, and I put some breakers in a separate disconnect box to control the appliances. A solar panel trickle-charged the battery whilst also running a small pump for the solar hot water system. 

In the end everything worked a little better than I expected. The prototype garnered a lot of interest from the public, so I'm currently drawing up a final product with one of my former teammates. Who knows, maybe you'll find one of these in a city near you sometime!


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