Rheostat and adding another battery to ebike for more volts

B

BrianVoltagegt500

1 mW
Joined
Dec 5, 2014
Messages
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I own a voltage gt 500 that has 4 12 volt 12ah batteries in series running to a 500 watt motor. my question is this, i wish to ad another battery of proper output and ah to increase range and some speed, but i wish to be able to dial in the power via a rheostat or potentiamer type switch so that i can turn up the power from say 1 volt to 12 volt to 24 volts ( if i choose to add a 24 volt battery instead of 12 volt). The idea being that i don't want to blow the controller which now is probably a 48 volt controller tho when the bike is charged up fully and then plugged in the voltage reading is 55 volts, so perhaps it has a 60 volt controller. my question is this i want to plug in the extra battery via the charger input since the bike runs with the charger plugged in or whether i just plug in a dead end connection i picked up but haven't hooked up a battery to yet, so i am assumming that plugging in a battery at this port will add a battery in series since the charger seems when plugged in to run in series. ok here's the question, i read i need to use a rheostat to dial up and down the power from the added battery, but since it's probably in series i will probably need a rheostat that can handle 60 or more volts and 12 ah, i contacted a company that says they have rheostats that can handle that voltage, but they need to know the ohms, i have no idea what the ohm are for this system, how do i figure that out? anybody out there done this before with a rheostat or can recommend a better way to dial in the power as i want or need it to go the longer distances i wish?. I would like to hear your stories if you attempted this type of modyfication.

Brian
 
I own a voltage gt 500 that has 4 12 volt 12ah batteries in series running to a 500 watt motor. my question is this, i wish to ad another battery of proper output and ah to increase range and some speed, but i wish to be able to dial in the power via a rheostat or potentiamer type switch so that i can turn up the power from say 1 volt to 12 volt to 24 volts ( if i choose to add a 24 volt battery instead of 12 volt). The idea being that i don't want to blow the controller which now is probably a 48 volt controller tho when the bike is charged up fully and then plugged in the voltage reading is 55 volts, so perhaps it has a 60 volt controller. my question is this i want to plug in the extra battery via the charger input since the bike runs with the charger plugged in or whether i just plug in a dead end connection i picked up but haven't hooked up a battery to yet, so i am assumming that plugging in a battery at this port will add a battery in series since the charger seems when plugged in to run in series. ok here's the question, i read i need to use a rheostat to dial up and down the power from the added battery, but since it's probably in series i will probably need a rheostat that can handle 60 or more volts and 12 ah, i contacted a company that says they have rheostats that can handle that voltage, but they need to know the ohms, i have no idea what the ohm are for this system, how do i figure that out? anybody out there done this before with a rheostat or can recommend a better way to dial in the power as i want or need it to go the longer distances i wish?. I would like to hear your stories if you attempted this type of modyfication.

Brian
 
BrianVoltagegt500 said:
....so i am assumming that plugging in a battery at this port will add a battery in series since the charger seems when plugged in to run in series....
Click to expand...

That is a bad assumption and you will likely damage something doing such or if lucky, just blow a fuse. Better get a handle on how that stuff works before attempting modifications. And a rheostat isn't a viable option for in line control of battery power.
 
I'm not sure if I understood the question.

You wish to add a battery in series to increase your voltage, then reduce it again with a resistor in series?


They are asking what resistance. If you decide to add a 24v battery, and wish to be able to null the full 24v, Then to stop this 24v getting to the controller it must instead appear across your resistor. I will side step now and look at another aspect of this conversion. The resistor will need to carry the 15? amps of your system, and drop 24v. That is a power dissipation of W=VxI = 360w being eaten up by your resistor. It's going to be prohibitively big hot and heavy, while munching your entire extra battery.
 
That's what a controller does. The throttle tells it how much power to give. Turn down the throttle and you get less power to go further. It should be adjustable from zero power to maximum.
 
Don't go over 59v unless you know what's inside your controller. Over volting can blow your controller. A three speed switch can give you more range.
 
friendly1uk said:
I'm not sure if I understood the question.

You wish to add a battery in series to increase your voltage, then reduce it again with a resistor in series?


They are asking what resistance. If you decide to add a 24v battery, and wish to be able to null the full 24v, Then to stop this 24v getting to the controller it must instead appear across your resistor. I will side step now and look at another aspect of this conversion. The resistor will need to carry the 15? amps of your system, and drop 24v. That is a power dissipation of W=VxI = 360w being eaten up by your resistor. It's going to be prohibitively big hot and heavy, while munching your entire extra battery.
Click to expand...


it will munch all the battery power up before i need it when i hit about the 15 mile mark ( about 1 hour ride) or eat just a percentage?

any other ideas how to do this?
 
999zip999 said:
Don't go over 59v unless you know what's inside your controller. Over volting can blow your controller. A three speed switch can give you more range.
Click to expand...

three speed switch? is that to turn on off the extra battery or a dial up power in 3 switch mode?
what's it called by name?
 
d8veh said:
That's what a controller does. The throttle tells it how much power to give. Turn down the throttle and you get less power to go further. It should be adjustable from zero power to maximum.
Click to expand...

yes i know about the controller, but i don't want the extra power to burn out the controller until existing batteries start to read low, then want to dial in more of the extra battery, know how that can be done?
 
major said:
BrianVoltagegt500 said:
....so i am assumming that plugging in a battery at this port will add a battery in series since the charger seems when plugged in to run in series....
Click to expand...

That is a bad assumption and you will likely damage something doing such or if lucky, just blow a fuse. Better get a handle on how that stuff works before attempting modifications. And a rheostat isn't a viable option for in line control of battery power.
Click to expand...


yes that is why i am asking on this board as well as electricians etc, why do you say a rheostat isn't a viable option for in line control of battery power?
if no with that, then what do you suggest?
 
You need to know how many volts your controller can take, and use them all. No more, as it will die, and no less, as the effect on longevity is not great enough to warrant voltage dropping complexity and losses.

We can't really guess what the controller is. We need to look. Sticker detail may help, but a look inside is better. We want to look at the capacitors. The electrolytic one's in particular. They have easy to read labels.
 
From your original post I gather your goals are primarily increased range, and secondly increased speed.

Your idea of using a rheostat doesn't sound appropriate at all, even if you knew your controller could handle more volts. Also know that other systems on your moped are likely made for the 48v system..such as the charger, the gauges, lights, etc. Regardless, even if you got a rheostat installed without damaging anything, all the rheostat is going to do is waste a large portion of the power by shorting it through a resistor.

The best, easiest, safest, and cheapest way to achieve your goal is to add batteries in parallel with the ones you have. Your moped uses sealed lead acid batteries (SLA). Since they are SLA, they probably aren't balanced during charge and discharge, so its very likely that the bike only uses the ground and 48v out of the battery pack (ie, it doesn't tap into the 12v,24v,and 36v between the batteries). So all you have to do is add a basket or rack on the back and fit another 48V battery pack that you make by connecting four 12V SLA's in series. Then add a plug to the moped battery pack and put them in series. Since your bike motor is 500W, it is probably advisable to put a 20A fuse in line with your new battery pack.

Before you attach the new pack you need to make sure that both the old and new packs are at the same voltage by connecting them in parallel with a resistor between. Of course this isn't to urgent for SLA, but still good practice.

With double the battery capacity, you will have more power avialable for twice as long, and your range will be doubled.
 
Dougt said:
From your original post I gather your goals are primarily increased range, and secondly increased speed.

Your idea of using a rheostat doesn't sound appropriate at all, even if you knew your controller could handle more volts. Also know that other systems on your moped are likely made for the 48v system..such as the charger, the gauges, lights, etc. Regardless, even if you got a rheostat installed without damaging anything, all the rheostat is going to do is waste a large portion of the power by shorting it through a resistor.

The best, easiest, safest, and cheapest way to achieve your goal is to add batteries in parallel with the ones you have. Your moped uses sealed lead acid batteries (SLA). Since they are SLA, they probably aren't balanced during charge and discharge, so its very likely that the bike only uses the ground and 48v out of the battery pack (ie, it doesn't tap into the 12v,24v,and 36v between the batteries). So all you have to do is add a basket or rack on the back and fit another 48V battery pack that you make by connecting four 12V SLA's in series. Then add a plug to the moped battery pack and put them in series. Since your bike motor is 500W, it is probably advisable to put a 20A fuse in line with your new battery pack.

Before you attach the new pack you need to make sure that both the old and new packs are at the same voltage by connecting them in parallel with a resistor between. Of course this isn't to urgent for SLA, but still good practice.

With double the battery capacity, you will have more power avialable for twice as long, and your range will be doubled.
Click to expand...


by putting 48 more volts in parallel that would make a total of 96volts, controller can't handle that, the rheostat is so that i can plug in another battery but keep it lower than 60 volts at first, but as the existing batteries lose juice i want to dialup more from the backup to keep up the speed and range.
the whole idea is i am assuming i have a 60 volt controller so i am trying to stay below 60 volts but close to it even as my voltage drops with use, thus increasing range, speed, i want to do a round trip of 24 miles to beach and back. if i knew i had a 70 volt or more controller i wouldn't even bother considering a rheostat.
 
So this is what you have. http://sarasotascooters.com/product/voltage-vm-500-gt/

Everything on this scoot is made to handle 48v. So there is not much you can do to increase speed a lot. But a larger size 48v battery, or a 48v battery that sags less and weighs less than lead would improve it's performance a lot.

I'd look into a 48v 20 ah lifepo4 (or other lithiuim) battery for it, like a pingbattery. This will more than double your range, and your speed won't be 1 mph less every couple miles, till you are crawling.

Lifepo4 will run many miles before it sags and slows down, unlike lead that starts slowing more and more every mile you ride.
 
BrianVoltagegt500 said:
by putting 48 more volts in parallel that would make a total of 96volts, controller can't handle that, the rheostat is so that i can plug in another battery but keep it lower than 60 volts at first, but as the existing batteries lose juice i want to dialup more from the backup to keep up the speed and range.
the whole idea is i am assuming i have a 60 volt controller so i am trying to stay below 60 volts but close to it even as my voltage drops with use, thus increasing range, speed, i want to do a round trip of 24 miles to beach and back. if i knew i had a 70 volt or more controller i wouldn't even bother considering a rheostat.
Click to expand...

I think you are confusing parallel with series. Putting them in parallel would mean the same voltage, but double the capacity and double the battery current capability (but current is likely limited by your controller).

You need to check your controller, but it is likely about 50-60V max, because 12V batteries aren't really 12V...that is the nominal voltage, not the peak voltage. The peak charge your controller would see right now is during charging, and that is typically up to 15.6V max for a 12V SLA battery charger, but more likely around 13V-14V. So your system probably charges at 4x that or close to 56V. After removing the charger, your fully charged battery should be about 4x12.6=50.4V.

If you add another battery to your pack to make it into a 60V pack, your batteries would charge very slowly and never reach full capacity...not even close. And any voltage hic-up may blow the fets in your controller.

So basically you have two options:
1) just add another 48V pack in parallel. Easy and cheap.
2) buy a new higher voltage controller. Figure out how to wire it to your existing system (they aren't all the same). And rewire you current pack for a higher voltage, by adding more batteries in series. You risk damaging your motor and other electronics too, especially when going full power up long steep hills.

As for the rheostat, it is basically a big variable resistor. If you want to control voltage with one by putting a higher voltage pack in parallel with a lower voltage one, you would have to continuously dump energy from the higher voltage pack through the resistor, as it maintains the max charge on the lower voltage battery (or you need some beefy diodes on each pack so they only power the motor). That isn't a sound engineering principle unless you only plan to ride a couple miles between charges, as your higher voltage battery will quickly discharge until it matches the lower voltage battery. I would give up on that idea. Even using a large dc-dc converter would be better.
 
dogman dan said:
So this is what you have. http://sarasotascooters.com/product/voltage-vm-500-gt/

Everything on this scoot is made to handle 48v. So there is not much you can do to increase speed a lot. But a larger size 48v battery, or a 48v battery that sags less and weighs less than lead would improve it's performance a lot.

I'd look into a 48v 20 ah lifepo4 (or other lithiuim) battery for it, like a pingbattery. This will more than double your range, and your speed won't be 1 mph less every couple miles, till you are crawling.

Lifepo4 will run many miles before it sags and slows down, unlike lead that starts slowing more and more every mile you ride.
Click to expand...


yes that's the bike, how do you know it's 48 volt controller? because when i fully charge it and then plug in the charger the voltage meter next to the speedometer reads 55-56 volts and the bike starts to slow down when the voltmeter reaches 46 volts. how could it initially read 50-55 volts when i first start my ride if the controller should blow out at 48 volts? are you guessing or read this somewhere? if read it can you give me the page info?

i am afraid to use lithium because of the fire hazard, they say you shouldn't even charge the batteries if you are not constantly present, and i charge when i am sleeping at night so that's out. do you know anything about rheostat option i am thinking of? carry an extra 12v or 24v and dial in some more voltage as needed?

if you know the controller on the bike do you know where i can get a 72 volt controller replacement?

thx
 
Dougt said:
BrianVoltagegt500 said:
by putting 48 more volts in parallel that would make a total of 96volts, controller can't handle that, the rheostat is so that i can plug in another battery but keep it lower than 60 volts at first, but as the existing batteries lose juice i want to dialup more from the backup to keep up the speed and range.
the whole idea is i am assuming i have a 60 volt controller so i am trying to stay below 60 volts but close to it even as my voltage drops with use, thus increasing range, speed, i want to do a round trip of 24 miles to beach and back. if i knew i had a 70 volt or more controller i wouldn't even bother considering a rheostat.
Click to expand...

I think you are confusing parallel with series. Putting them in parallel would mean the same voltage, but double the capacity and double the battery current capability (but current is likely limited by your controller).

You need to check your controller, but it is likely about 50-60V max, because 12V batteries aren't really 12V...that is the nominal voltage, not the peak voltage. The peak charge your controller would see right now is during charging, and that is typically up to 15.6V max for a 12V SLA battery charger, but more likely around 13V-14V. So your system probably charges at 4x that or close to 56V. After removing the charger, your fully charged battery should be about 4x12.6=50.4V.

If you add another cell to your pack to make it into a 60V pack, your batteries would charge very slowly and never reach full capacity...not even close. And any voltage hic-up may blow the fets in your controller.

So basically you have two options:
1) just add another 48V pack in parallel. Easy and cheap.
2) buy a new higher voltage controller. Figure out how to wire it to your existing system (they aren't all the same). And rewire you current pack for a higher voltage, by adding more batteries in series. You risk damaging your motor and other electronics too, especially when going full power up long steep hills.

As for the rheostat, it is basically a big variable resistor. If you want to control voltage with one by putting a higher voltage pack in parallel with a lower voltage one, you would have to continuously dump energy from the higher voltage pack through the resistor, as it maintains the max charge on the lower voltage battery (or you need some beefy diodes on each pack so they only power the motor). That isn't a sound engineering principle unless you only plan to ride a couple miles between charges, as your higher voltage battery will quickly discharge until it matches the lower voltage battery. I would give up on that idea. Even using a large dc-dc converter would be better.
Click to expand...
0lbs

yes your right i mixed up parallel with series, not enough room on the bike for a full 48 volt battery system, the bike is 140lbs as it is now, maybe adding parallel one 12 volt would get me the distance i want yes have considered that. more amp hours but not highter voltage is good.
 
BrianVoltagegt500 said:
i am afraid to use lithium because of the fire hazard, they say you shouldn't even charge the batteries if you are not constantly present,
Click to expand...

'They' don't have proper ev packs and chargers, 'they' have a stack of lipo and an RC charger. As such 'they' have a lot of fires.

The people that buy proper stuff don't need to watch. We don't have to do anything. Just push a plug in. It might be wise to not go far, but if you were to charge 13 phones you would be in more trouble. Or a couple of laptops. These cells are in everything and may fail at any time. Charging or sat on the shelf. Mainly in use though. Unless you treat them like RC gear, then they mostly fire up when charging. User error is always the blame. Which makes people think it won't happen to them. If you let a bms do it all for you, One storage fire reported. Do it yourself and you waste days of your life swapping wires around, then you will be rewarded by a fire or three. There is simply no gain from doing it wrongly. Just extra expense, extra work, extra risk. That is in over 90% of cases, including yours.

Proper bikes, phones, laptops, curlers, ups units, they all use a stack of cells and a bms to do all the work. Non tell you to stand over them. That is just people that insist their bike is a model and must be charged as such. Finding any way to claim it can be done safely. You realise at RC shows they are made to charge outside in flame proof containers? Their are a lot of people out there we just can't help, so keeping them away if your best bet.



You might be able to buy a new battery that simply fits. It will contain the right bits. Meaning you will need the correct charger to, but it will be a good set.

I have seen lipo pretending to be lead recently. I'm not sure how you would use it, but someone will.... It's charging them in series I'm unsure of, and there is no way on this planet you should be re-wiring them to charge.
 
A 48v lead battery would charge to about 56v. You have a "48v" controller. More importantly, all the other stuff on the bike runs on "48v".

So you pop a 72v controller on that bike, and blam, there goes everything else on your bike. Your lights, speedo, etc etc. 72v will fry all the smaller electronic stuff on the bike.

What you need is a nice safe, 48v 20 ah lifepo4 battery. This is not the burn your house down lithium, not the stuff used in quad copters that you need to watch.

A 20 ah Lifepo4 will give you huge range, and won't drop in voltage so fast as you ride, so most of your ride will be a LOT faster than now. Most of your ride will be at about 54v, after starting out at about 60v. ( which your bike can handle) With lead, you are dropping to 48v just about right away, 6v slower.
 
BrianVoltagegt500 said:
Ibut i wish to be able to dial in the power via a rheostat or potentiamer type switch
Click to expand...

Why? That's what your throttle already does, using your existing controller.

If you DO try it, you'll need a "rheostat" that's bigger and heavier than your motor, probably bigger heavier than all your batteries and motor combined, to do it.

Look up Luxtrol lighting controls, there are pics of one type in some of my posts here. You'll need a bigger one than the kind I have here.
 
BrianVoltagegt500 said:
yes your right i mixed up parallel with series, not enough room on the bike for a full 48 volt battery system, the bike is 140lbs as it is now, maybe adding parallel one 12 volt would get me the distance i want yes have considered that. more amp hours but not highter voltage is good.
Click to expand...
Nope.

YOu won't get anything at all out of adding a single extra battery in parallel with one of your existing batteries, other than a heavier bike and a lighter wallet.

YOu have to add a separate one in parallel with EACH of the existing ones to get something out of it.

OR you can add a single one in *series* with the existing ones to get higher voltage and slightly higher watt-hours. (assuming your controller and other electronics can handle it--they might not be able to)
 
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