Correct charged and discharged voltage for 48v SLA ?

[redorblack]

Just got done with a 22 mile ride on my Rans Wave with a PedalGreen 360 watt front hub motor running 4 10ah SLA batteries. I completely forgot (again) to check the voltage when I got back... want to know what a safe discharge level is. Also want to know if 55v straight off the charger (13.75v per battery) is ok.

Only used the motor for assist on grades/hills since I was on a group ride, Glad to see that the fastest rider in our group (races road bikes) couldn't keep up on the hills to my recumbent that is normally doing a 1/3 the speed I could maintain today with assist. My goal was to see how much juice I used just hanging with the group, glad to say I only had one bar flicker out on the throttle as we finished the ride (under load) and I was playing with more throttle near the end. I suspect that with a 15ah LiFePo4 pack I could have done the entire course at wide open throttle and been back in less than half the time the group takes.

 

[317537]

I do regular testing of SLAs.

Straight off the charger at 55v is good. Rest for an hour about 13.3v per batt.

On a 22 mile 35km ride you're doing well at 10ah and they should be pretty flat. Reading around 12v at rest. My 24ah can do 10 miles run 100 lbs of shopping another 10 miles and still have 12.3v over the terminals.

Anything under 12.5v is going to shorten the life of your battery. On an average 15 mile no shopping trip I could come home with batteries well above 12.6v.

anything that draws your voltage down below 12v is killing your batteries in 6 mths or sooner.

 

[Russell]

Yes 13.75V per 12V SLA is a perfectly normal float voltage however you must remember that everything above ~13.2V, the normal fully charged voltage for lead-acid chemistry, will dissipate in a couple of hours after the batteries are removed from the charger or in a few seconds of use. Fully discharged for SLA's is about 10.5V per 12V SLA but you need to check it under load since the voltage will jump back up when you stop drawing current.

-R

 

[317537]

Yes 13.75V per 12V SLA is a perfectly normal float voltage however you must remember that everything above ~13.2V, the normal fully charged voltage for lead-acid chemistry, will dissipate in a couple of hours after the batteries are removed from the charger or in a few seconds of use. Fully discharged for SLA's is about 10.5V per 12V SLA but you need to check it under load since the voltage will jump back up when you stop drawing current.

-R

Yea an SLA under no load at 10.5v is a very dead to be SLA. I try to aim for voltage levels above 12.4v if possible and keep dod well above 50% if I can. I lose .3 of a volt under load at 12.7v taking it down but above 12.4v. My batts are new so I am hoping they will come into their full strength over the next month or so, then its a down hill with capacity. More energy and less capacity. My old SLA were really good about four weeks before they died.

The problem being is that SLA become dead weight soon enough and they start killing themselves. The more lead you have the more they start to overdraw to power themselves during take offs and up hills more, the more perkins effect triggers lvc . The older they get this effect is worse. SLA's do not need LVC IMO. On one of my brushed controllers LVC reduces the currnet draw via PWM, LVC reduces PWM to the gates. You dont notice anything other than reduced speed until its acts like dead you need to push it to get it going. Works very well with SLA's and pedal assist.

4 X 10ah batts is better then 4 old X 24ah with a reduced capacity. If there was a way to shed those lbs as the battery got older this would be ideal. Even if we came up with a led alloy aloy to reduce the weight of SLA tech with the new carbon technology discovered this would put led acid above and beyond nimh and this is quite a significant step towards keeping the old SLA's head above water.

 

[Russell]

Yea an SLA under no load at 10.5v is a very dead to be SLA. I try to aim for voltage levels above 12.4v if possible and keep dod well above 50% if I can. I lose .3 of a volt under load at 12.7v taking it down but above 12.4v. My batts are new so I am hoping they will come into their full strength over the next month or so, then its a down hill with capacity. More energy and less capacity. My old SLA were really good about four weeks before they died.

Yes keeping the DOD to 50% will greatly increase the longevity of SLA's however in practice on an ebike that is gonna be pretty tough for most folks unless they carry a great deal of lead along with them. In my case the SLA's I used came with the kit and I knew I would be replacing them so I didn't care, I took them close to fully discharged on most rides. The best advice for ANY e-biker is to get rid of their lead acid batteries and get something better.

-R

 

[317537]

Yes keeping the DOD to 50% will greatly increase the longevity of SLA's however in practice on an ebike that is gonna be pretty tough for most folks unless they carry a great deal of lead along with them. In my case the SLA's I used came with the kit and I knew I would be replacing them so I didn't care, I took them close to fully discharged on most rides. The best advice for ANY e-biker is to get rid of their lead acid batteries and get something better.

-R

Yeah I carry 60lbs of lead all ready on my bike and am looking for new chemistry next battery change. I want something a little more perminant.

Because I tinker too much, using SLA's for a year or two at the begining of my learning all about E-bikes, I feel was a good move as I would no doubt run into too many problems and the expense would of outweighed the advantages.

The tech and method has improved considerably along with a good decrease in price since.

I am studying packs and chemistry more than 6mths before I invest. I am a little sick of changing stuff around and rather ride the thing then fix it all the time.

 

[redorblack]

Yikes... so what voltage would equate to 50% DOD?

I just found something else out... I added 'another' 10ah battery to get 48v and it stuck up a bit in the bag. The jumper I got with it had copper coated female terminals and keep popping off on rough downhills.

So... I found the 4th steel looking terminal I got with the kit and went to put it on and decided to pull the batteries out to see why the one sat higher than the others...

3 batteries are 7.5ah and the 1 added is a 10ah. So... I actually have been doing my trips on significantly less juice than I realized.

With SLA am I going to hurt it having the 4th battery being 2.5ah higher in capacity or are they forgiving enough?

This may change my mind about what capacity I need in LiFePo4... I've been thinking 10/15/20ah... with 15 being the sweet spot for my range needs based on what SLA was doing at 10ah (assuming I was getting 6ah out) Now I'm wondering if I'm getting 8-10 miles wide open throttle and 22 miles just as needed.... how far will 10 or 15 take me in the real world with LiFePo4? Maybe a 10ah Ping or Headway would do just fine... can add another one later in parallel or with a switch if needed I guess.

 

[Russell]

This chart gives you a pretty good idea about the SOC for SLA's based on their resting voltage;




If you always keep the 4 batteries together as a series group and charge them that way then you should not have a problem with the one larger battery. The three 7.5Ah batteries will die before the 10Ah of course but at that point you won't have much usable current to continue on. If you were using three 10Ah and one 7.5Ah battery it would be a different story, in that case you'd probably ruin the smaller battery very quickly if you deep cycled the pack then charged it as a group.

Are you using a controller with a LVC designed for 36V (~31.5V) or 48V (~42V)?

If you are riding conservatively now on purpose to extend your range then you get a BIG battery and don't conserve you won't get the range you might have envisioned. I use as much as 66% more power per mile now that I have a 48V/10Ah LiFePO4 compared to the early days of eight months ago when I nursed a 36V/9Ah SLA pack (5.4Ah max. usable) as far as 32 miles. It is hillier where I live now but for the most part I use more power because I ride faster and probably contribute less.

-R

 

[317537]

Wow I average at around 60% dod. Today i did 16kms and against a really heavy wind on the way home. came back at 12.81 and the lowest batt at 12.78 within 10 seconds of pulling through the garage door I tested her.

The smaller slas wont like the high current chargers and the bigger batts would prefer a lower volt with the lower current charger. You cant win with different sized SLA's in series unless you do some pretty heavy voltage division over the series.

 

[redorblack]

This chart gives you a pretty good idea about the SOC for SLA's based on their resting voltage;




If you always keep the 4 batteries together as a series group and charge them that way then you should not have a problem with the one larger battery. The three 7.5Ah batteries will die before the 10Ah of course but at that point you won't have much usable current to continue on. If you were using three 10Ah and one 7.5Ah battery it would be a different story, in that case you'd probably ruin the smaller battery very quickly if you deep cycled the pack then charged it as a group.

Are you using a controller with a LVC designed for 36V (~31.5V) or 48V (~42V)?

If you are riding conservatively now on purpose to extend your range then you get a BIG battery and don't conserve you won't get the range you might have envisioned. I use as much as 66% more power per mile now that I have a 48V/10Ah LiFePO4 compared to the early days of eight months ago when I nursed a 36V/9Ah SLA pack (5.4Ah max. usable) as far as 32 miles. It is hillier where I live now but for the most part I use more power because I ride faster and probably contribute less.

-R

Thanks for the chart.

I haven't put a voltmeter on the batteries yet with it discharged. Completely forgot after getting back from my 22 mile test ride. I did a 'calibration' for the 48v setup when switching up from 36v. Consisted of hooking up two white wires on the controller, turning the key on and opening the throttle... wait for the wheel to stop shaking, unplug the wires, replug them and go wide open throttle for 8-10 seconds with the wheel spinning. Turn it off, unplug the calibration wires and it's done.

Now as to what that actually does... I have no idea. I think my LED fuel gauge on the throttle is still set for 36v, and I'm wondering if there is a LVC at this point. Running the 22 miles with VERY conservative usage (mostly no usage) except on grades where I pulled several miles of 3-10+% climbing I had one light blinking out right at the end and plenty of power/speed left. When I went downtown wide open throttle and back I got about 8 miles and there wasn't much of anything left for assist by the end... red light only with it under load and it didn't do much of anything up the last roller.

The last ride, my intention was to measure the voltage (had my meter ready...) as soon as I got back in the house with the bag 'o batteries. Unfortunately I zoned and instead plugged the charge in by habit when I set the bad down. Didn't realize it until an hour later.. Aurgh! So the only real data I had was my charged voltage with it straight off the charger.

I've been working and it's been raining since, so the bike is in the garage and the batteries are sitting on the bench in the kitchen staying warm and charged.

I'm off light duty so hopefully can afford a cycleanalyst and a LiFePo4 battery pack soon. Need to decide if a Ping or a Headway setup is the way to go and what I'll need to make the investment last.

 

[dnmun]

lifepo4 first, set aside all funds for that first, especially if you are considering another SLA for bigo buckos.

if you have a Voltmeter, then you can make jumpers for it and carry it with you wired into your battery to monitor the battery until you get a CA. or Watts Up. that is good to 60V i think so you could even fit a 48V lifepo4 into a WU.

 

[redorblack]

lifepo4 first, set aside all funds for that first, especially if you are considering another SLA for bigo buckos.

if you have a Voltmeter, then you can make jumpers for it and carry it with you wired into your battery to monitor the battery until you get a CA. or Watts Up. that is good to 60V i think so you could even fit a 48V lifepo4 into a WU.

Hi dnmun,

Not going higher voltage, ordered up the CA from Methods the other day. Hopefully Stephen or Travis makes it to the Tacoma EV meeting tomorrow night with a Headway 48v/10Ah pack, otherwise I'll have to drive down to Lacey to check them out.

Tonight I finally remembered to hook up my meter after a ride, only went about 4 miles, full throttle the whole way. Voltage after getting back in the house was 51.1v which according to that chart is somewhere between 60 and 80% charge? Not a very accurate method is it?