I've got an idea kicking around about adding a 12V SLA in series between the controller and the motor.
Can anyone tell me if this will work or what problems it might cause? I appreciate all responses.
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Support V is for Voltage
The Controller uses the inductance of the Motor to regulate the current of its output.
The Voltage across the motor is following the pulses of the controller.
There usually is a diode across the output of the controller allowing the current to continue to flow.
FALSTAD Simlutor URL with Info: Bat - Controller - Motor
I tried link and it works with Vis4V.
Your idea could work if Boost battery stray capacitance was not to large.
I've set the Motor Bemf to 50V that causes Regen to the 48V battery , then with realy off the extra 12V Boost makes the motor a load.
The Falstad Simulator is a cheats way to bypass alot of maths.
Have a look at the help info and the other circuits to learn how to build your own.
This new version 1.5m has a File>URL Link Export Feature which I used to make the link above.
What kind of controller and battery voltage where you thinking of and what type of motor.
Only Brushed DC motors would work with this boost cicuit using a relay.
Not that many people use these any more (on their Bikes lots o EV cars do though), they use brush-less that needs an AC current onto multiple coils.
Have fun.
7¢
Thanks for the simulator. I'll look forward to playing with that later.
This is going in a small scooter. Just trying to put new things together for fun and learning.
I will have (4) 12V SLA's in the main pack and one for the boost battery. Motor is a DC Brushed about 750W.
Was just hoping to find a way to add some speed without having to replace the controller, A popular mod for small scooters is to simply add a battery and overvolt the existing components. Some controllers don't like that, so I was searching for a solution that would not put the extra voltage through the controller.
Thanks for your response. I may have some follow-up questions once I start playing with the simulator.
The Max Voltage ratings of the existing controller are in question.
In theory the Boost Battery doesn't increase the voltage seen by the controller.
But there are conditions where if the Boost battery was linked in by the relay the current will not be controlled.
If you where stopped and hit the "Boost" Button the current would flow through the Controller Output Bypass Diode.
That could be fun for a wheel spin, but likely to BLOW stuff up.
Controller are "CONTROLLERS" for a reason.
Also when your at max speed on the 48V pack then switch to Nitro-Boost and go for 60V on motor pushing higher speeds.
But to make this work you need relay that will need to switch over with high currents flowing causing lots of arc wear on the contacts.
The Boost battery
A separate charger for the battery.
Compared to upgrading the Controller MOFETs and capacitors and other bits (if you know what the circuit is, which is unlikely).
Having a 12V battery on the Scooter is good for accessories like Head light, Phone/MP3 charger, Entertaining Musical Horn Set.
So if you also has a 48V to 13.8 Volt DC/DC isolated or maybe inverting type, would get you far without battery imbalance. (I've just recently found my hoarded 60V to 12V DC/DC's - Not sure if they work though)
The Boost 12V battery contributes 1/5th the Output power. so a 300W DC/DC would keep it the 12V boost battery was tiny compared to the main batteries.
Or you just use the same size and use a small DC/DC to top-up removed power from the Boost/Accessory Battery.
Just remember your Controller could Die if it Gets over 100V Bemf from the Motor.
But I'd give it a go if you want to play around with all the extra wiring and relays, and not want the simplicity of a 60Vnom controller.
7©
I appreciate your responses! That's the info I was looking for.
I know it would be simpler to just use a controller that can handle 60V without question, but I just gotta play!
btw, I have a White Rodgers Type 124 6-terminal solenoid to do the high current switching. It's rated for 400A inrush on the N.O. contacts, so I think it should be safe enough. I don't plan to engage this until I'm up to speed. I've done something similar to another scooter. I used the same size solenoid and completely bypassed the controller and connected the motor directly to the 48V pack. I had a motorcycle kill switch on the handlebar, and another hooded safety switch in series so I wouldn't accidentalyy bump the button when I wasn't ready.
I've got the batteries wired for parallel charging with one 12V charger. I can easily charge up the extra battery with one of my 12V chargers.
Thanks again for your help.
It doesn't matter whether you put the extra battery on the battery side, or the motor side.
the controller (well the gates) still sees the extra voltage.
The other problem is, the freewheel diodes conduct when the back emf is above 1V, and the gates are off.
meaning if you put a 12v battery on the motor side, it will short across the freewheel diodes.
Matt
Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km
So, one of you says the controller WILL see the added voltage and the other says NOT, and so now I don't know.
I don't see this. The output with a boost battery in the circuit is a series voltage source that is summed/added to the Output voltage
The battery its self won't cause the MOSFET or Capacitor Voltage Max Ratings to be exceeded.
As the Main Battery is in parallel with the DC Bus it will keep it clamped to the main Battery Voltage.
The Supply inductance is the big issue that causes MOSFET and Capacitor Voltage limits being reached.
Keep the supply inductance low compared to the DC bus capacitance.
This Boost battery will give a (60/48) 25% boost to max speed.
When max Boost speed is reached and the Boost is released and the Bemf from the Motor is across the Controller there will be a large current passing back to the Batteries.
This is like going down a steep hill and going beyound the Kv rating of Motor with 48V across it.
This could cause current to flow in the MOSFET intrinsic diode (or on die).
The resistances in the circuit will determine the current flow. I'd say the Lead-Acid Batteries will be the biggest resistance
Motor Torque at speed is all about current through the motor.
The speed (motor RPM) will set the Bemf, so the 12v difference will cause significant recharge currents into the main pack with the BOOST Battery not in circuit.
The inductance of the motor will also stop the current from changing rapidly.
I wonder if the Simulator can be used to show this?
The controller Diode Conducts the Current as the Motor inductance wants to maintain the same current flow.
So the current flowing through the Controller Diode doesn't mean its not going to work.
When the Gate is OFF the Boost battery will be forcing current through the motor.
When slowing down the Bemf from the Motor can't recharge the BOOST battery via the flyback diode but can get current to flow through the MOSFET diode if the Bemf is above the combined Main and Boost battery potential (60V).
As e-doggies mentioned he won't (but likely will) enable the Boost will the motor is at 0 RPM.
If he did the Free-wheeling diode would complete the circuit and the motor would torque up to a large uncontrolled current. Say the Motor resistance was (R = P/V^2 = 750W/(48x48) = 0.32 Ohm)
So the current would be 12V/0.32 = 37A
Have you had any luck understanding the Falstad Simulator?
Falstad Sim CCt: Boost now 12V and variable Bemf plus other bits
I found that it failed simulation if relay switch released. But if Simulation Speed was slow it was okay.
Circuit is getting pretty complicated.
True, so motor stopped is the worst case scenario.
with the controller off, the full voltage of all batteries on either side are added.
theres no Bemf to take away from this.
most "48v" controllers use 75V fets.
using a 60v nominal pack gives a just off charge voltage of 74v.
adding a 12v battery to the output of the controller will bring the voltage across the junction to ~88v.
if only inserting the boost battery once back emf is above 12v, then that will be ok, as you rightly stated.
if the voltage across the junction goes too high, the Fet will short.
which particular motor is this?
all the DC motors I have seen have had resistances that are well below 0.1 Ohm (or above 120A shorting out a 12v battery)
Matt
Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km
Ah I can see what your suggesting, that the M- terminal would see 48V + 12V = 50V and fully charged Max : 56V + 14V = 60V
But the Fly back diode will conduct and clamp the B+ to M+ voltage to -1V. So the Fet will only see 56V - (-1V) = 59V
most "48v" controllers use 75V fets.
using a 60v nominal pack gives a just off charge voltage of 74v.
adding a 12v battery to the output of the controller will bring the voltage across the junction to ~88v.[/quote]
If the controller normally is at 48V Nominal and 12V Boost then 56V + 14V = 60V
So if the FETs are 75V then they would be okay.
Here is an other update of a simulator circuitbats at full charge and Boost