Safe to add 6v to my battery?

[Pinesal]

My bike has a 48v 24ah SLA battery pack. I want to give it a little 6v boost by adding two parallel 6v 12AH SLA batteries in series with the pack. What is the likelihood of this causing problems for the motor and/or controller.

My second question is, I have a battery charger that charges to 60v. I think this is about perfect for a 54v pack but the charger was technically designed for a lithium battery. Will it still work?

Thanks for your advice.

 

[Jon NCal]

I don't think the charger would be appropriate voltage. 48v would mean 24 cells, plus 3 makes 27 cells. Depending on the type of SLA, you would want to charge at 2.30 to 2.35 volts per cell. Your charger would supply 60v/27cells = 2.22 volts per cell, too low.

 

[wesnewell]

The charger will still work, it just won't quite get you a full charge. 60/27=2.222V per cell.
https://en.wikipedia.org/wiki/Float_voltage

 

[Punx0r]

Most 48V controllers will take 60V max.

 

[wesnewell]

Every 48V controller I've ever seen had at minimum 63V caps and 68-75V fets. Now since i haven't used anything below 72V rated in years. things could have changed, but I doubt it. Some/most/all newer controllers with lcd displays do limit voltage to 60V or the display that controls the controller won't turn it on, but it can be bypassed.

 

[skeetab5780]

Yes this will work on discharge anyway...I used to do this on my first ebike almost a decade ago while waiting for fund for lifepo4...

I had 48v 12ah of SLA and I would add one more 6v 12ah for more top speed. It was heavy but worked no problem on a 48v controller.

I charged then separate tho since it was easier for me to unplug the 6v and use chargers I had kicking around.

 

[johninclaflin]

I had trouble doing this with a 36v mini controller from ebikelife SWXH-R kit. I already had success overvolting the kit to 48v with SLA. When I series wired another 6v in, if the batteries were fresh off the charger it wouldn't come up, but if they were a little used, good to go. I wrote down voltage of battery string to controller from an inline watt meter, but can't lay my hands on that. I thought about riding the bike out of town in 48v, and then switching in the 6v a couple miles down the road, but it seemed like too much hassle and easier to just get a higher rated controller which I'll do someday.

 

[skeetab5780]

Its because the controller was only 36v and not 48v

It more than likely only has 50v capacitors in it instead of 63-75v

Sounds like it may have a safety feature in place to save it from frying tho that is handy

 

[999zip999]

24ah and 12ah these is capacity. Must unplug the 12ah pack half way through. Or else. Always keep sla charged. They do poorly sitting half charged or dead.

 

[Pinesal]

24ah and 12ah these is capacity. Must unplug the 12ah pack half way through. Or else. Always keep sla charged. They do poorly sitting half charged or dead.

I am connecting two 12AH batteries in parallel to make 24AH to match the other batteries. That's the way it works right?

Anyway, I added he batteries and it works perfectly. I have a modest speed boost that I am happy with.

But now my concern is the low voltage cut-off on the controller. I think it's 42v. Wouldn't that be too low and damage my batteries if it gets that low? Anyone have some advice on this?

 

[mailseth]

Relevant, very interesting, article written by spinningmagnets:
https://www.electricbike.com/52v-battery-3077-fet/

Take away points:
- 48v is mostly due to a multiple of legacy 12v SLA systems
- In general, MOSFETs that can handle 48v can actually handle up to 60v

 

[Jon NCal]

24ah and 12ah these is capacity. Must unplug the 12ah pack half way through. Or else. Always keep sla charged. They do poorly sitting half charged or dead.

I am connecting two 12AH batteries in parallel to make 24AH to match the other batteries. That's the way it works right?

Anyway, I added he batteries and it works perfectly. I have a modest speed boost that I am happy with.

But now my concern is the low voltage cut-off on the controller. I think it's 42v. Wouldn't that be too low and damage my batteries if it gets that low? Anyone have some advice on this?

I would try not to go below 1.75 volts per cell. 27 cells x 1.75 = 47.25v total string voltage. Best to stop before you get down to 48.0 volts on your meter.

 

[Pinesal]

24ah and 12ah these is capacity. Must unplug the 12ah pack half way through. Or else. Always keep sla charged. They do poorly sitting half charged or dead.

I am connecting two 12AH batteries in parallel to make 24AH to match the other batteries. That's the way it works right?

Anyway, I added he batteries and it works perfectly. I have a modest speed boost that I am happy with.

But now my concern is the low voltage cut-off on the controller. I think it's 42v. Wouldn't that be too low and damage my batteries if it gets that low? Anyone have some advice on this?

I would try not to go below 1.75 volts per cell. 27 cells x 1.75 = 47.25v total string voltage. Best to stop before you get down to 48.0 volts on your meter.

Do you think there might be a way to modify my bike's built in battery meter? It doesn't show voltage, just bars.

 

[999zip999]

Ok reread two 6v 12ah added or 6v 24ah in series with a 48v 24ah original battery set up. Monitor with a cheap voltmeter.

 

[Pinesal]

I don't think the charger would be appropriate voltage. 48v would mean 24 cells, plus 3 makes 27 cells. Depending on the type of SLA, you would want to charge at 2.30 to 2.35 volts per cell. Your charger would supply 60v/27cells = 2.22 volts per cell, too low.

So, a full charge should measure 62v?

 

[Jon NCal]

Please see, for more detail, partly depends on temperature:
http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

 

[Pinesal]

I thought I would give a little update to this. Taking the advice in this thread, I decided that the 60v charger wasn't going to cut it. So I went and bought a cheap 6v/12v charger to charge the 6v pack. So I installed a switch in line between the 6v battery and the 48v pack that, when set to one position, cuts the 6v battery out and allows the bike to operate and charge as if the extra battery wasn't there. This mode is for charging the batteries. The other position adds the 6v back into the system for riding.

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