Lowering the LVC of a controller

[sophocha]

Hi guys,

I have just managed to build my own e-bike from zero with the help of the atomic zombie guide. It is a 60v 1000w bike that is fast and exciting. My problem is this: I have 5 12v SLAs (17ah) in series (edited) and when I travel for about 10km everything is fine, but then gradually the motor is making five second stops and the battery indicator blinks. This gradually worsens up until the 18-20km range.I think this is due to a very high LVC of the controller (low voltage cut) which is around 56v! My batteries start full at 65v but when I reach around 62v the stoppage happens ( i have still 12.4v left on each battery when this happens).Is there a way to lower the LVC? I have seen just one other thread talking about this and putting a resistor in series with another resistor to lower the LVC by a few volts, but I'm not an electrical engineer and I cannot pinpoint the LVC circuit on the board (I have circled the area on the photo that I think is the LVC circuit) . If anybody can help me out I would appreciate it.

Thanks

 

[Ykick]

This is one of those reasons why I buy programmable controllers. Change LVC through computer software.

Yes, there’s probably a mechanical way (resistor network) to accomplish it but PCB’s vary from run to run and without a good understanding of operation and rework skills you might duff something while in there?

Another thing is that SLA’s incredibly saggy after the initial top charge has burned off, battery chemistry from this century might be all you need with the current controller?

 

[sophocha]

So do you think a jump to a custom made 60v lithium pack will solve the problem? Is 56v LVC suitable for it?....or maybe go 72v by adding another sla battery

This is one of those reasons why I buy programmable controllers. Change LVC through computer software.

Yes, there’s probably a mechanical way (resistor network) to accomplish it but PCB’s vary from run to run and without a good understanding of operation and rework skills you might duff something while in there?

Another thing is that SLA’s incredibly saggy after the initial top charge has burned off, battery chemistry from this century might be all you need with the current controller?

 

[sophocha]

Well, apparently there is an option in the KT-LCD3 display that changes the LVC by up to 2V. I have to test this out and see if it changes something.

This is one of those reasons why I buy programmable controllers. Change LVC through computer software.

Yes, there’s probably a mechanical way (resistor network) to accomplish it but PCB’s vary from run to run and without a good understanding of operation and rework skills you might duff something while in there?

Another thing is that SLA’s incredibly saggy after the initial top charge has burned off, battery chemistry from this century might be all you need with the current controller?

 

[sophocha]

nope, a jump to 72v increased my range by 5km but that is all. That high LVC is killing me! Help

 

[nutnspecial]

Hey ya! Why do you want to sag your lead below 11v per battery? ime they don't like that much, at all. It sounds like you may be getting fairly normal expected performance out of that 17ah lead acid, depending on the amp draw.

However, if you want to monitor the batteries yourself realtime, I'd suggest possibly a simpler fix and eliminating the lvl altogether. I however also am not an EE and have no idea how to do that, or modify a hard set lvl.

But to me sounds like the battery is the problem.

5 12v SLAs (17ah) in parallel

What would be telling for me would be to take those 5 in series, and then parallel another string to see if you still have the same problems approaching LVL. Or drop your amperage draw if possible.

My couple hundred ah bank sags like crazy with .5c load. Guaranteed the bottom soc is wasted should I try to maintain that rate of discharge.

 

[dogman dan]

The problem is, your controller is trying to save your lead, but you are not.

If you are going to stick with lead, it needs to be higher AH, so it lasts longer and sags less. Too much controller for the batteries you have. You may also have completely wrong type of lead battery. Some sla's still cannot handle a motor, and large controller.

You can lower the power your controller draws, possibly with the display.

 

[sophocha]

You are correct...it is the controllers fault, trying to save my batteries...when the stops occur i still have 12.4v left on each battery...plenty of juice left...56v of lvc is more suited to lithium batteries rather than sla.

The problem is, your controller is trying to save your lead, but you are not.

If you are going to stick with lead, it needs to be higher AH, so it lasts longer and sags less. Too much controller for the batteries you have. You may also have completely wrong type of lead battery. Some sla's still cannot handle a motor, and large controller.

You can lower the power your controller draws, possibly with the display.

 

[beast775]

If your bike is fast and exciting on sla they wont last long :lol:

 

[footloose]

Nice bike, looks like fun! Really rewarding to build from scratch, plus if you built it... then you can fix it.

Easy for me to spend your money ( :wink: ), but think a different battery might be the answer.
The bike would be much lighter without the lead ballast.
And much sleeker.
Probably even more exciting.
Maybe something like this if you've got the cash? http://lunacycle.com/72v-panasonic-pf-11-6ah-with-luna-charger/

 

[John in CR]

...That high LVC is killing me! Help

No, like Dogman said the LVC is trying to save you from yourself. The problem is the horrible lead batts you're hauling around. Their voltages sags under load so badly in the lower half of their discharge cycle that it trips the LVC. Many of us started with lead, so we feel your pain, but they're really not economical anymore compared to lithium batts except maybe for very short hauls with a vehicle on relatively flat ground if weight isn't a concern.

Once you consider that only about 50% of that SLA's rated capacity can actually be drawn from SLA batteries if you want them to last any reasonable time (a year or more), the fact that good lithium batteries have far greater life and weigh about 1/4th or less, the economical choice is clear. Sure use lead as a cheap way to get into the game to prove to yourself that electric is better, but you've done that, and now it's time to really have fun. A much lighter battery with far greater capacity and power will be a huge step up for you. I assure you that you'll thank us later, as long as you don't try to "cheap out" and go for the cheapest ready-made lithium pack you can find, as that route is filled with suspect vendors. If economics is the primary concern then hit up recycling centers and other means of finding used lithium to recycle. I have multiple packs still in us that I made in 2008 and 2009 from used toolpack and other lithium batteries.