# Need Safety tips for large motors/batteries/capacitors

C

#### [email protected]

Jan 1, 1970
0
First of all hey to everyone who reads this group, hope your well.

Anyways, in my latest project I am hooking up 2 OSMC's (open source
motor controllers, www.robotpower.com) to 4 wheelchair motors to power
a small chair around.

1st set of Questions, regarding the batteries:
I have 2 24 volt UPS batteries (which are actually 2 12 volt 17 AH
Lead Acid batteries in series) that I would like to use.

I have read that with NiMH batteries, they need to be connected to
bridge rectifiers ala http://www.tlb.org/scooter_battery_schematic.html
to prevent current flowing into eachother.
Is this also required for Lead Acid batteries?

I eventually plan to drop some serious dinero's for Lithium Polymer
batteries, do those require the rectifier in parrallelling
applications?

Finally for batteries, does anyone know of a link for a robust 24 volt
battery charger schematic? Unbolting the batteries from eachother is
tiresome, and I would prefer to be able to hook the entire battery
network up a charger and not have to worry about it.

2nd set of Questions, regarding the capacitors:
I recently found 7 25V 30,000uF electrolytic capacitors at a local
surplus store, which I must admit just scare the bejeezus out of me.

Now according to the manufacturer of the UPS that the batteries were
ripped out of, the batteries have a nominal charging voltage of 27.6
or 28 volts or something in that area. If I connect these fully
charged batteries to the circuit, will the caps be damaged by the over
voltage?

How many of them should I use? the motors are 3 amps no load, and 8
amps full load, so in absolute worse case scenario there would be 32
amps drawn from the caps. is 210,000 uF overkill?

When I put the battery in the circuit, the first thing it does is
charge the caps. It occurs to me that if I charged up the caps as
well, it would give my application that much extra longevity between
charges.

I have charged little caps before, but since these are like big white
scary hand grenades I would just like a little brush up so they dont
burst into flames/explode whatever. So essentially what is the best
way to charge 7 x 30,000 uF caps up to 24 volts?

Thats all I can think of for now, if anyone wants to go ahead and
reply, that would be absolutely great, and much appreciated. And if
anyone has any resources about building electric vehicles with
wheelchair motors link would also be appreciated.

E

#### ehsjr

Jan 1, 1970
0
First of all hey to everyone who reads this group, hope your well.

Anyways, in my latest project I am hooking up 2 OSMC's (open source
motor controllers, www.robotpower.com) to 4 wheelchair motors to power
a small chair around.

1st set of Questions, regarding the batteries:
I have 2 24 volt UPS batteries (which are actually 2 12 volt 17 AH
Lead Acid batteries in series) that I would like to use.

I have read that with NiMH batteries, they need to be connected to
bridge rectifiers ala http://www.tlb.org/scooter_battery_schematic.html
to prevent current flowing into eachother.
Is this also required for Lead Acid batteries?

I eventually plan to drop some serious dinero's for Lithium Polymer
batteries, do those require the rectifier in parrallelling
applications?

Finally for batteries, does anyone know of a link for a robust 24 volt
battery charger schematic? Unbolting the batteries from eachother is
tiresome, and I would prefer to be able to hook the entire battery
network up a charger and not have to worry about it.

2nd set of Questions, regarding the capacitors:
I recently found 7 25V 30,000uF electrolytic capacitors at a local
surplus store, which I must admit just scare the bejeezus out of me.

Now according to the manufacturer of the UPS that the batteries were
ripped out of, the batteries have a nominal charging voltage of 27.6
or 28 volts or something in that area. If I connect these fully
charged batteries to the circuit, will the caps be damaged by the over
voltage?

How many of them should I use? the motors are 3 amps no load, and 8
amps full load, so in absolute worse case scenario there would be 32
amps drawn from the caps. is 210,000 uF overkill?

When I put the battery in the circuit, the first thing it does is
charge the caps. It occurs to me that if I charged up the caps as
well, it would give my application that much extra longevity between
charges.

I have charged little caps before, but since these are like big white
scary hand grenades I would just like a little brush up so they dont
burst into flames/explode whatever. So essentially what is the best
way to charge 7 x 30,000 uF caps up to 24 volts?

Thats all I can think of for now, if anyone wants to go ahead and
reply, that would be absolutely great, and much appreciated. And if
anyone has any resources about building electric vehicles with
wheelchair motors link would also be appreciated.

At 32 amps draw, 210,000 uf will do nothing for you. As a point
of information, when using caps like those you always want to
use a voltage _lower_ than the cap is rated. Exposing them to
a voltage higher than their rating is something to avoid.

Regarding using diodes to isolate the batteries - bridges
are not required. I would use the diodes, regardless of
which type of batteries you use. You can use a single diode
for each series battery setup, like this:

+--[Batt+]-[Batt+]-[Batt+]-[Batt+]-[Batt+]-[Diode]--+
| |
+--[Batt+]-[Batt+]-[Batt+]-[Batt+]-[Batt+]-[Diode]--+---> +
|
+-------------------------------------------------------> -

You need a different charging algorithm depending on battery
chemistry - you don't want to charge NiMh, Lead Acid and
Lithium with the same charger, unless it is programmable
for those types. Otherwise, you need a separate charger for
each chemistry.

Ed

P

#### Paul E. Schoen

Jan 1, 1970
0
ehsjr said:
First of all hey to everyone who reads this group, hope your well.

Anyways, in my latest project I am hooking up 2 OSMC's (open source
motor controllers, www.robotpower.com) to 4 wheelchair motors to power
a small chair around.

1st set of Questions, regarding the batteries:
I have 2 24 volt UPS batteries (which are actually 2 12 volt 17 AH
Lead Acid batteries in series) that I would like to use.

I have read that with NiMH batteries, they need to be connected to
bridge rectifiers ala http://www.tlb.org/scooter_battery_schematic.html
to prevent current flowing into eachother.
Is this also required for Lead Acid batteries?

I eventually plan to drop some serious dinero's for Lithium Polymer
batteries, do those require the rectifier in parrallelling
applications?

Finally for batteries, does anyone know of a link for a robust 24 volt
battery charger schematic? Unbolting the batteries from eachother is
tiresome, and I would prefer to be able to hook the entire battery
network up a charger and not have to worry about it.

2nd set of Questions, regarding the capacitors:
I recently found 7 25V 30,000uF electrolytic capacitors at a local
surplus store, which I must admit just scare the bejeezus out of me.

Now according to the manufacturer of the UPS that the batteries were
ripped out of, the batteries have a nominal charging voltage of 27.6
or 28 volts or something in that area. If I connect these fully
charged batteries to the circuit, will the caps be damaged by the over
voltage?

How many of them should I use? the motors are 3 amps no load, and 8
amps full load, so in absolute worse case scenario there would be 32
amps drawn from the caps. is 210,000 uF overkill?

When I put the battery in the circuit, the first thing it does is
charge the caps. It occurs to me that if I charged up the caps as
well, it would give my application that much extra longevity between
charges.

I have charged little caps before, but since these are like big white
scary hand grenades I would just like a little brush up so they dont
burst into flames/explode whatever. So essentially what is the best
way to charge 7 x 30,000 uF caps up to 24 volts?

Thats all I can think of for now, if anyone wants to go ahead and
reply, that would be absolutely great, and much appreciated. And if
anyone has any resources about building electric vehicles with
wheelchair motors link would also be appreciated.

At 32 amps draw, 210,000 uf will do nothing for you. As a point
of information, when using caps like those you always want to
use a voltage _lower_ than the cap is rated. Exposing them to
a voltage higher than their rating is something to avoid.

Regarding using diodes to isolate the batteries - bridges
are not required. I would use the diodes, regardless of
which type of batteries you use. You can use a single diode
for each series battery setup, like this:

+--[Batt+]-[Batt+]-[Batt+]-[Batt+]-[Batt+]-[Diode]--+
| |
+--[Batt+]-[Batt+]-[Batt+]-[Batt+]-[Batt+]-[Diode]--+---> +
|
+-------------------------------------------------------> -

You need a different charging algorithm depending on battery
chemistry - you don't want to charge NiMh, Lead Acid and
Lithium with the same charger, unless it is programmable
for those types. Otherwise, you need a separate charger for
each chemistry.

Ed

I just looked at some battery management ICs on websites for TI, Linear
Technology, and Maxim. They are a little pricey but may be worthwhile for a
high end application. The big picture seems to be Li-Ion, but they have
multichemistry chargers and some that are programmable and integrate a
"fuel gage". They have switching type chargers up to about 4 amps in single
IC packages. I have decided to try to roll my own using a PIC.

Energy storage for the capacitors is based on 1/2*C*V^2, so your 210,000 uF
25 V bank will store 65 J (watt-seconds). If you have 800 watts of motors
(1 HP), the energy will power the vehicle for less than 0.1 seconds. They
are most useful for quick energy dumps from dynamic braking, but you will
need more than that to absorb the kinetic energy of a fast stop.
Supercapacitors are available, such as Maxwell BPAP1200 – E270, which are
1200 F at 2.7 V. Ten in series gives you 120 F at 27 volts, and energy
storage of 43,000 W-Sec, or 50 seconds run time at 800 watts. They cost
about $46 each. You might do best with two independent systems so you don't need to parallel the batteries. You should be able to connect the controllers so they synchronize motor speed, and you probably want to have a speed differential for turning. For any high power circuitry, it is a good idea to have it enclosed in a rugged electrical box, and wear eye protection when testing. Judicious use of fuses and other current limiting devices is also advised. Good luck, Paul S #### [email protected] Jan 1, 1970 0 First of all hey to everyone who reads this group, hope your well. Hope my well what? Seriously, have a look at this http://www.buchmann.ca/toc.asp and Yahoo groups for relevant interests. The power assist group is knowledgeable about batteries controllers and motors for bicycles. Then there are scooter parts houses for cheap Chinese motors, controllers and batteries. There is one in Australia called Oatley Electronics at http://www.oatleyelectronics.com/ jack C #### Coleston Jan 1, 1970 0 At 32 amps draw, 210,000 uf will do nothing for you. As a point of information, when using caps like those you always want to use a voltage _lower_ than the cap is rated. Exposing them to a voltage higher than their rating is something to avoid. Regarding using diodes to isolate the batteries - bridges are not required. I would use the diodes, regardless of which type of batteries you use. You can use a single diode for each series battery setup, like this: +--[Batt+]-[Batt+]-[Batt+]-[Batt+]-[Batt+]-[Diode]--+ | | +--[Batt+]-[Batt+]-[Batt+]-[Batt+]-[Batt+]-[Diode]--+---> + | +-------------------------------------------------------> - You need a different charging algorithm depending on battery chemistry - you don't want to charge NiMh, Lead Acid and Lithium with the same charger, unless it is programmable for those types. Otherwise, you need a separate charger for each chemistry. I just looked at some battery management ICs on websites for TI, Linear Technology, and Maxim. They are a little pricey but may be worthwhile for a high end application. The big picture seems to be Li-Ion, but they have multichemistry chargers and some that are programmable and integrate a "fuel gage". They have switching type chargers up to about 4 amps in single IC packages. I have decided to try to roll my own using a PIC. Energy storage for the capacitors is based on 1/2*C*V^2, so your 210,000 uF 25 V bank will store 65 J (watt-seconds). If you have 800 watts of motors (1 HP), the energy will power the vehicle for less than 0.1 seconds. They are most useful for quick energy dumps from dynamic braking, but you will need more than that to absorb the kinetic energy of a fast stop. Supercapacitors are available, such as Maxwell BPAP1200 - E270, which are 1200 F at 2.7 V. Ten in series gives you 120 F at 27 volts, and energy storage of 43,000 W-Sec, or 50 seconds run time at 800 watts. They cost about$46 each.

You might do best with two independent systems so you don't need to
parallel the batteries. You should be able to connect the controllers so
they synchronize motor speed, and you probably want to have a speed
differential for turning.

For any high power circuitry, it is a good idea to have it enclosed in a
rugged electrical box, and wear eye protection when testing. Judicious use
of fuses and other current limiting devices is also advised.

Good luck,

Paul- Hide quoted text -

- Show quoted text -

Thats awesome, thanks for the advice. Ok, so when I get around to
charger for it, cause they have expensive and I dont want to screw
them up, so the multi chemistry charger is not really an issue, thanks

For the lead acid batteries they are fairly simple to charge from what
ive seen, so I want to whip up a charger for them.
I see the wisdom of seperating the circuits to keep the batteries
seperate, Ground from the 2 circuits should be tied together tho,
correct?

Now the motors I have a geared down to 260 or so RPM's, with a worm
storage from braking is not such an issue, as the mechanical segment
has to soak up any excess energy during braking.

The super caps are interesting, especially since I have been reading
about these fantastical claims from eestor in texas, do you have any
resources on charging them? I was just under the impression that all
motor driver circuits require big caps in parallel with the motors,
for acceleration from a dead start, should I not put them in the
circuit? What would be the optimal capacitor arrangement for
gearmotors?

As for fuses and current limiting devices, what sort of thing would be
best? I am most concerned with shorts, so a fuse for about 40 amps
would probably do the trick. Gotta check for DC breakers, hmmm.

Do you happen to know the code for 15 amp diodes? Are those still of
the 1N4*** series? Also, I think in the end I am going to put all teh
motor circuitry in an enclosed oil filled box for extra robustness and
heat dissipitation, so I dont need to massively over design all the
parameters, when i was in school I saw a 1N4002 take 8 amps for over
20 minutes by being enclosed in a barrel of oil.

Sorry for all the annoying questions, just with the last motorized
vehicle I attempted to build I blew all sorts of hip4080's and the
busbar for all my caps melted and a variety of other silly mishaps
that I would like to avoid this time.

Thanks a ton
-Coleston

C

#### Coleston

Jan 1, 1970
0
Hope my well what?

Seriously, have a look at thishttp://www.buchmann.ca/toc.asp
and Yahoo groups for relevant interests. The power assist group is
knowledgeable about batteries controllers and motors for bicycles.
Then there are scooter parts houses for cheap Chinese motors,
controllers and batteries.
There is one in Australia called Oatley Electronics athttp://www.oatleyelectronics.com/

jack

ton.

P

#### Paul E. Schoen

Jan 1, 1970
0
Coleston said:
[snip]
I just looked at some battery management ICs on websites for TI, Linear
Technology, and Maxim. They are a little pricey but may be worthwhile
for a
high end application. The big picture seems to be Li-Ion, but they have
multichemistry chargers and some that are programmable and integrate a
"fuel gage". They have switching type chargers up to about 4 amps in
single
IC packages. I have decided to try to roll my own using a PIC.

Energy storage for the capacitors is based on 1/2*C*V^2, so your 210,000
uF
25 V bank will store 65 J (watt-seconds). If you have 800 watts of
motors
(1 HP), the energy will power the vehicle for less than 0.1 seconds.
They
are most useful for quick energy dumps from dynamic braking, but you
will
need more than that to absorb the kinetic energy of a fast stop.
Supercapacitors are available, such as Maxwell BPAP1200 - E270, which
are
1200 F at 2.7 V. Ten in series gives you 120 F at 27 volts, and energy
storage of 43,000 W-Sec, or 50 seconds run time at 800 watts. They cost

You might do best with two independent systems so you don't need to
parallel the batteries. You should be able to connect the controllers so
they synchronize motor speed, and you probably want to have a speed
differential for turning.

For any high power circuitry, it is a good idea to have it enclosed in a
rugged electrical box, and wear eye protection when testing. Judicious
use
of fuses and other current limiting devices is also advised.

Good luck,

Paul- Hide quoted text -

- Show quoted text -

Thats awesome, thanks for the advice. Ok, so when I get around to
charger for it, cause they have expensive and I dont want to screw
them up, so the multi chemistry charger is not really an issue, thanks

For the lead acid batteries they are fairly simple to charge from what
ive seen, so I want to whip up a charger for them.
I see the wisdom of seperating the circuits to keep the batteries
seperate, Ground from the 2 circuits should be tied together tho,
correct?

Probably a good idea, and should be bonded to chassis.
Now the motors I have a geared down to 260 or so RPM's, with a worm
storage from braking is not such an issue, as the mechanical segment
has to soak up any excess energy during braking.

The super caps are interesting, especially since I have been reading
about these fantastical claims from eestor in texas, do you have any
resources on charging them? I was just under the impression that all
motor driver circuits require big caps in parallel with the motors,
for acceleration from a dead start, should I not put them in the
circuit? What would be the optimal capacitor arrangement for
gearmotors?

You need to look at the surge current requirements for the motors and the
capacity of the batteries. The capacitors can help reduce high current
surges through the batteries, as well as a lower ESR to keep voltage
As for fuses and current limiting devices, what sort of thing would be
best? I am most concerned with shorts, so a fuse for about 40 amps
would probably do the trick. Gotta check for DC breakers, hmmm.

Many AC breakers are also rated for DC use, but inductive loads can be a
real problem if snubbers or freewheeling diodes are not installed (or are
defective). Sometimes two or three poles are hooked in series to get higher
DC rating. Fuses are ultimately more fail-safe, but expensive and
cumbersome to replace. Fast blow and even high speed semiconductor fuses
are probably best for DC. It's probably a good idea to put a fuse on the
positive terminal of each large capacitor if they are in parallel. Ordinary
250 volt or 600 volt fuses at 40 amps should not be too expensive. I bought
a lot of DC rated high current breakers surplus on eBay for a couple bucks
each. If you need a few I'll get more details on them if it's worthwhile to
ship some (from 21030). My company designs and builds breaker test sets, so
I can check them out.

Do you happen to know the code for 15 amp diodes? Are those still of
the 1N4*** series? Also, I think in the end I am going to put all teh
motor circuitry in an enclosed oil filled box for extra robustness and
heat dissipitation, so I dont need to massively over design all the
parameters, when i was in school I saw a 1N4002 take 8 amps for over
20 minutes by being enclosed in a barrel of oil.

I think the oil filled box would be more trouble than it's worth, and
possibly dangerous. Just a strong steel NEMA type enclosure should be fine
for blast containment. If anything, you might consider filling it with very
clean sand.

Sorry for all the annoying questions, just with the last motorized
vehicle I attempted to build I blew all sorts of hip4080's and the
busbar for all my caps melted and a variety of other silly mishaps
that I would like to avoid this time.

Sounds like my kind of fun!

Paul