# Trickle Charge



## Crippleicious (Feb 10, 2012)

Hello all,

Again with my noob questions. But can you trickle charge DC lifepo4 batteries, from say a solar panel or back up generator? If so how do i even go about wiring that into the system? 

Thank you for the time,
Kenny


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## major (Apr 4, 2008)

Crippleicious said:


> ... But can you trickle charge DC lifepo4 batteries, from say a solar panel or back up generator?


Hi Crip,

Trickle charging typically means to take a fully charged battery and apply a small charge current to it equal to its self discharge current in order to keep it fully charged during periods of nonuse. Since most lithium batteries have next to no self discharge, classic trickle charging should not be applied. If you continue to charge a lithium cell past its "full" state you will damage it and possibly cause external damage such as a fire.

With lithium batteries you can charge at low current for a long period but must monitor the state of charge (of each cell for safe systems) and stop charging when they are full (100% SOC) or at a SOC just under full for a safety factor. This is where the BMS comes in handy 

Regards,

major


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## Crippleicious (Feb 10, 2012)

Thanks Major, 

Is there a way to charge the batteries in a state of use? Like switching on a back up generator while driving the car to restore some power on a long trip?


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## major (Apr 4, 2008)

Crippleicious said:


> Is there a way to charge the batteries in a state of use? Like switching on a back up generator while driving the car to restore some power on a long trip?


Well no, but yes, kind of 

When a battery is in use it is a source and delivers charge to a load. When you charge a battery it becomes the load and takes charge from a source like a generator. So when you put all three together at once (battery, load and generator), the battery takes the difference of current between the generator and load. If that difference is positive (generator current greater than load current) the battery will charge. If that difference is negative (load current greater than generator current), the battery will discharge. If the load and generator currents are equal, the battery remains at the same SOC taking or giving no charge.

So you can't actually charge and discharge the battery at the same instant in time. But over a use duty cycle where the load varies, the battery can be charged and discharged during that time period. 

Did I make that confusing enough?

major


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## Crippleicious (Feb 10, 2012)

HAHA so if I read that correctly while I was driving, if I had a generator running to the batteries it would help, even it the charge was going straight back out the battery to the motor. 

If i were to wire this would i wire it to the charger or somewhere else?


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## MalcolmB (Jun 10, 2008)

Just a thought - it's not exactly a simple solution, but if your solar output is between 36 and 75V you could use a DC/DC converter like this (ebay item 300567449485) to feed each lithium cell. The output voltage from the DC converter can be trimmed between 3.3 and 3.6V by adding a suitable resistor across the output pins. If you trim the output to 3.40V it could be left on all the time without worrying about overcharging a cell. I'm using some of these converters to charge my pack from a 45V supply. They will limit the current output to about 20A, but do get hot at that current level without a good heat sink. They're much easier to manage at around 10A output, or less, which means an input of around 50W per converter. I can give you more details if you're interested. There are other converters available that may be more suitable for your application.


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## Crippleicious (Feb 10, 2012)

All input in any form is welcome! I'm just trying to get ideas and info before I start any of this. =)


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## MalcolmB (Jun 10, 2008)

Could you give more details about your system and what it is you want to do?


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## Crippleicious (Feb 10, 2012)

I have not started the EV part of the project, still fixing up the body suspension and such. Just getting all my research done first. Trying to figure out how to wire in an outside charging source while in motion. If i could just wire it to the charger that would make things much easier especially if the charger has an auto shut off.

But i am planning on using a Transwarp11 with 144v200ah system using LiFePo4100ah cells. still unsure which controller or charger i will be using yet. Again still planning and researching everything


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## Crippleicious (Feb 10, 2012)

If I say wired the generator directly to the charger and employed the use of a BMS like this one (http://www.evassemble.com/index.php?main_page=product_info&cPath=6&products_id=46) shouldn't that keep all the lithium batteries all at a level state, allowing for the charging while in motion?


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## major (Apr 4, 2008)

Crippleicious said:


> If I say wired the generator directly to the charger and employed the use of a BMS like this one (http://www.evassemble.com/index.php?main_page=product_info&cPath=6&products_id=46) shouldn't that keep all the lithium batteries all at a level state, allowing for the charging while in motion?


Where does the power come from to keep the vehicle in motion?


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## Crippleicious (Feb 10, 2012)

Crippleicious said:


> But i am planning on using a Transwarp11 with 144v200ah system using LiFePo4100ah cells. still unsure which controller or charger i will be using yet. Again still planning and researching everything


The before mentioned LiFePo4's


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## major (Apr 4, 2008)

Crippleicious said:


> The before mentioned LiFePo4's


Where does the power come from to power the generator?


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## frodus (Apr 12, 2008)

Major,

I think he's talking about a backup generator, i.e. a gas generator, plugged into a charger, plugged into batteries connected to the controller.


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## Crippleicious (Feb 10, 2012)

frodus said:


> Major,
> 
> I think he's talking about a backup generator, i.e. a gas generator, plugged into a charger, plugged into batteries connected to the controller.


you would be absolutely correct!  I'm wondering if the Back up generator (gas powered) can run to the charger while the vehicle is in motion being powered by the LiFePo4's


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## major (Apr 4, 2008)

Crippleicious said:


> you would be absolutely correct!  I'm wondering if the Back up generator (gas powered) can run to the charger while the vehicle is in motion being powered by the LiFePo4's


O.K. Now you're taking about a hybrid. Using a gas engine powered "back-up" style 110VAC generator to run a battery charger while you're driving using the battery pack for propulsion power is really a bad choice. It is inefficient and polluting and unlikely to supply enough power to sustain the required propulsion power requirement let alone actually charge or maintain a charge on the battery.

Try it if you want. But you'll find it more economical and cleaner to use a vehicle designed for gasoline power or to devote the space and weight of the engine/generator to additional battery and charge at home.


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## Crippleicious (Feb 10, 2012)

This was just purely an example of a charging source while driving. Weather it be solar, a generator, or wind turbine. All I am wondering is if the charging source can be run to the charger while driving with a BMS.


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## major (Apr 4, 2008)

Crippleicious said:


> This was just purely an example of a charging source while driving. Weather it be solar, a generator, or wind turbine. All I am wondering is if the charging source can be run to the charger while driving with a BMS.


To do that, the power from the "charger" has to be greater than the power being used from the battery for propulsion. In which case you might as well use the power source for the charger to propel the vehicle directly because it will be more efficient. Like a hybrid vehicle. Or a gasoline powered vehicle. Or a sailboat.


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## Crippleicious (Feb 10, 2012)

Makes sense thank you.


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