48 volt to 36 volt

[jimmyg4life]

Hey Guys,
I have a 48 volt crystalyte I bought from largoscooters.com and to be honest I can't recall the motor number but I know it is a 4 series (I didn't get paper work) it does 24 mph @ full charge if this tells you anything. Now my question is it has a 48v 20A controller,cut off voltage 29v +/- 1v.
Now I run sla and want to up grade to lifepo4 but for cost I thought I would go to 36 volt 12ah. So I unhooked one of my batts to give me 36 volt to test how it ran but the yellow low light was on instantly , it ran ok though (just 3/4 of a mile) @ 18mph vs 24mph but does the instant yellow mean I would need a different controller ?? Also as far as the batteries how come the same ah rated batteries get different distance claims?? Say a 9ah sla has 12/13 mile where as lifepo4 or nimh has 27mi or 20mi respectively I mean isn't a ah a ah ?????? Thanks for any help
Jimmy G

 

[Larry]

I woudn't pay too much attention to the yellow light. My guess is that the motor and controller will work just fine at 36 volts. I run my 400 series motor and 20 amp crystalite controller at 36 volts. The yellow light on the throttle is set to come on when the voltage sags down to a set amount. Since it's a 48 volt throttle, the yellow light is probably set to come on when the battery pack sags down to around 42--43 volts or so (I don't know precisely). The throttle itself should work just fine with a 36 volt pack, though, since most of these throttles just use 5 volts anyway. It's just that the yellow low-battery light will not really tell you anything. It will always be lit up yellow with a 36 volt pack. For example, my 36 volt throttle yellow LED comes on at 31.5 volts.

36 volt LED throttles are cheap enuff--$10 to $15-if you end up with a 36 volt SLA pack and want the "low battery" yellow light feature. If you go with a 36 volt pack with some other battery chemistry besides SLA, a 36 volt "low battery" throttle won't be very useful anyway since other chemistries don't sag at the same rate as SLAs.



I

 

[gip_mad]

Hi, the yellow led is just a voltmeter embedded in your throttle; it does have nothing to do with the function of the ECU.
Since Li batteries have a very flat discharge curve, you shouldn't have any issue with the 29V limit.

For the other question, I guess that you can usually discharge a Pb battery 70-80% of its juice, while a Li battery can be drained closely to its max. capacity. We'll wait for an expert on that matter for the full answer!

 

[Larry]

I just re-read your post and realized I didn't comment on the second part of your question. The AH ratings of SLA batteries and other chemistries such as LifePO$ are really not comparable. SLA batteries sag a lot more and most people say you really can't expect to draw out more than about 60% of the AH rate capacity of SLAs on an ebike since the Slas sag so much (Peukert effect.) With most Lifepo4, you can actually draw out 80% to 90% of the amp hours. So, you should get more miles out of a 12ah Lifepo4 battery than you can out of a 12ah SLA battery.

However, the "C" rating of the actual cells making up the Lifepo4 battery need to be considered. If it is a battery that only puts out 1 c or 12 amps, then it won't be enuff amps to really power your 500 watt motor and your at least 20 amp controller very well and you may have problems with the BMS cutting out on you as well as stressing the battery too much may keep it from lasting as long as it should. Some people who bought smaller AH duct tape batteries and tried to run them on motors too big had these problems. If the cells can draw at least 2 c, I would think you would minimally probably be ok at 12ah, but I think I would go for a least 16ah on a Ping pack just to be safer.

Dogman is a big proponent of getting no less than 20ah, however, and he (or anyone else) may wish to dive in here with actual real world LifePO4 experience. I haven't purchased LifePO4 yet and am just repeating what I've read from other posters over the last year or so. I've just kind of concluded that 16ah will be the smallest Ping pack that I want. He's now using cells that are supposed to be a bit more powerful than his older cells were.

 

[Lessss]

Will you need a new controller? Depends on if there is a LOW VOLTAGE CUTOFF in the controller. Does the motor kick out for about 3 seconds then kick back in? If yes your controller has a LVC and that will need to be modified. His most respected from on high Fechter can tell you how if you send close up pics of your controller or better yet send the controller.

 

[mcstar]

The one thing I'd add to the AH conversation is that for SLAs, the AH ratin is its .1C rating whereas LiFePO4's are rated at much higher C's. For example, with the 12AH SLA you can expect to get 12AH only if you draw 1.2amps of continuous discharge. Since SLA's have the pukert effect, any discharge rate higher than 1.2 amps will result in you getting less total AH from the battery. When I used 12AH sla's on my e-bike, I usually lost power after around 5.4AH of discharge. This was even while going easy on the throttle and limiting my max current to 10amps or so. Once I upgraded to a 10AH LiFEPo4 (ping battery) I was able to run the throttle flat out, wide open the entire trip and use up 8-9AH or more without hitting the LVC of the battery. This increased my cruising speed substantially! I believe the ping batts are rated at 2C or more, and since my controller limited out at 20amps, I never had any issues.

Lately I've upgraded again to BMI batteries created for the hybrid auto market. These LIFEPO4 batteries are rated at 5C for 10AH. They are truely awesome batteries and can source bursts of up to 200amp . Yes, I know they are overkill for my setup, but I've been able to pull 12AH at full throttle with these and they are tested to live over 5000 recharges, so I'm confident they'll be around for many years and will have a lower TOC of ownership since I use them everyday.

 

[dogman dan]

Here we go... splash! Lotsa differences between one lifepo4 cell and another. I keep slogging the get the 20 ah sise because even if the cell is supposed to do 2 or 3 c, the bms might not be able to. For the majority of the options on ebay, there is no test results posted for more than 1 c, so to get the 1500-3000 cycles we hope for we have to stick pretty much to 1 c right? So what if we do 1.5c, does that not mean we get 1000-1500 cycles? Who knows, I don't? This is why I won't yet reccomend duct tape batteries for big motors unless they paralell several packs. Somebody will kill a battery for us eventually but so far, we don't know what the effect of 2 c on a battery from Li Ping will really be. He doesn't advise it. The other issue is what if the battery does go 3000 cycles at 15 miles per cycle? I sure don't expect my controller to go that far! and when you buy a new one, you will want a bigger one right? Again, better if you left some room for it. That battery could outlast several e bikes.

With the a123's and lifebatts etc, it's a whole new world of one hour charging and huge amps out of tiny packs. Out of my price range this year.

Run your bike awhile on three batteries. Stop when it gets real slow and check with a voltmeter if you need to, to not overdrain em on an experiment. If the controller doesn't act funny the LVC is no problem. With a battery from Li Ping, a 36v will really never get below 40v so LVC will be less of an issue anyway. You will soon expand your horizons to meet your range if you buy a 20 ah and not regret it. The 36v20ah will only weigh about 15 pounds so it will seem very small after 4 sla's. The only light I need on the throttle now is a light to tell me it's on. Pretty hard to ride far enough to need low batt.