Circuit design help needed

[big_s]

Hi all,

I need some help designing the circuit surrounding a new electric motor conversion.

I have a 48v battery bank; 4 x 12v 100ah Lithium batteries in series, each with internal bms. I plan on using these to power an electric motor via a sevcon controller.

The problem I have is how to wire up the charging circuit to support charging from a 12v solar panel(s), a 12v wind power generator, and a portable Honda 240v petrol generator/shore mains power.

So far I have purchased a Renogy boost charger that will allow charging at 48v from a 12v source. Can I connect this directly between the solar panel and the battery bank or do I need to go through some other kit so that I can charge and use the motor at the same time?

What would be a sensible set up to integrate the other charging sources. I expect solar and wind can be used to charge simultaneously, but could be disconnected when charging from either a portable generator or shore power?

The Sevcon controller and the Renogy charger are both CAN bus enabled if that is any help.

Any advice welcome. Ta!

 

[William_H]

I would expect the 12v to 48v charger to require something near 12 to 15v input. However if it is described as ok for 24v input as may be the case then you could just connect your '12v" ie 20v solar panel to the input. Unfortunately it is likely to have a switch mode power supply which tends to take more input current if input voltage falls to maintain the 48v output. With a solar source this can lead to pulling the voltage of the panel down sucking more current, pulling voltage down. This is in fact the reason solar controllers use a MPPT (Max Power Point Tracking) algorithm to get max power without over loading panel. This pull down effect will show up more with a smallish panel (relative power) or limited light conditions.
One solution (horrible) might be an MPPT solar controller to a 12v LA battery to the 12 to 48v charger. Hopefully the 12 to 48 has a low input voltage cut off to protect 12v battery.
Or get 2x domestic solar panels 40v each in series to a solar controller for lithium batteries. Sorry not much help perhaps just a bump of post. ol'will

 

[Lokmaly]

I don't have much info for you, but something you should look into if you want to take it further. You shouldn't just hook directly up to a power source. You need some sort of battery management system. Maybe look into Lithium Solar Charge Controllers.

 

[davidej]

A random thought!

could you design a circuit that would switch your four batteries from series to parallel.? When you need the motor it would be on series (48V) and for charging they would be in parallel (12V).

Easy Peasy if you can find an eight pole double throw switch capable of taking the requisite current.

 

[Boater Sam]

How are you going to switch off all the supplies when the lithium battery is almost fully charged? They live longer if only taken to 90%.

 

[big_s]

Hi all and thanks for the responses so far. Some initial thoughts:

1. The solar panel will be around 150W, so the standard roughly 20V and 7.5 amp output - the voltage in my original posting was wrong.
2. The Renogy Boost Charger is designed to take the out put from such a solar panel and boost it, providing an output voltage that can be specifically set to charge 4 x 12v Lithium batteries, and using MPPT.
3. Switching between usage and charging is possible but not a desirable option for me; the battery bank is effectively only 100ah and so charging while using the batteries will significantly increase the range/distance.
4. I presume the Renogy Boost charger will take care of the battery bank re not overcharging, and the batteries also have integrated BMS's so should not allow anything to damage them.

So the issue is how to combine multiple sources so that I can use the motor but also charge from whatever source happens to be providing charge.

I suppose I could get a charge controller for each source but I'm not sure if it is safe to connect all these charge controllers in parallel with the battery bank.

Ingoring the application of a motor, how do charging systems more generally combine multiple charge sources?

Is it safe to run the motor and charge at the same time? I have previously created a solar installation that used a Steca controller; this had inputs for the solar panel and the battery and output for the load. I presume the Steca internally switches between allowing current from the solar to the battery, and current from the battery to the load, but not both sumultaneously? The Renogy Boost charger does not have a load output; it is simply a charger.

Cheers.

 

[William_H]

Hi all and thanks for the responses so far. Some initial thoughts:


Ingoring the application of a motor, how do charging systems more generally combine multiple charge sources?

Is it safe to run the motor and charge at the same time? I have previously created a solar installation that used a Steca controller; this had inputs for the solar panel and the battery and output for the load. I presume the Steca internally switches between allowing current from the solar to the battery, and current from the battery to the load, but not both sumultaneously? The Renogy Boost charger does not have a load output; it is simply a charger.

Cheers.

Generally with lead acid batteries charge controllers charge on the basis of the voltage of the battery. So if a battery receives a charge from a wind turbine then if the battery is charged ie voltage high then it will limit charge from any other source (solar) as well. So simple charge controllers limit charge to avert over charge. So no concern. A smart charge regime will still go back to float charge when battery is charged regardless of what charged the battery. If it does manage to provide a high boost charge voltage from a shore power charger or even solar controller that high voltage would signal any other charger source to shut down. Any load on the battery like motor running would pull battery voltage down so enabling any charge source to run full charge.
I would expect any lithium BMS to function in the same way. ol'will

 

[big_s]

Hi all. Thanks for your replies.
Seems the Renogy Boost charger is an ideal fit as it has a User** customisable charging profile that I can modify (using an via bluetooth dongle) to suit the battery bank of 4x 12v Lithium I have.
Charging in parallel seems fine as long as the multiple chargers have suitable similar charging parameters set, so that they can all contribute to charging. If not, as William_H noted, some charge sources may switch off while others act as the charge source(s).
Charging and consuming at the same time is fine as long as the batteries have enough charge that the current from the charging sources does not trigger over current drain.
Cheers,
S.