72 volt charge controller

[windstuffnow]

  I've been pondering the idea of charging a 72 volt battery bank with solar and wind.  The charge controllers available don't come close to this voltage.  It dawned on me the other day that all I really need is a dump controller that would monitor the voltage of 1 battery.  

  If the controller was connected to a relay that would handle any load I might need then the controller only needs to monitor 1 battery in the bank.   When its charged, assuming all others are equal, the controller would activate the relay and start diverting the excess.  

  I have some 150 volt 600 amp and 300 amp transistors that would work instead of using a mechanical relay.   I think these would work quite nicely.

  Are there any problems that might occur using this arrangement?

  I'll be posting some pictures in my diaries in a couple weeks about the project.   It's basically a reverse trike electric vehicle with a 72 volt system.  I just cant stand the idea of plugging it in to the grid.  

  My goal this year is to find solutions for electric, transportation, and home heating.   The first one is easy, the second one I'm working on, the last one presents some challenges...

[kurt]

Zubbly did this exact thing to dump power from his 48v battery bank to a set of heaters in his furnace duct. he used a "mike controller" hooked to one of the 12v batteries in the series string sensing the voltage of that one battery but dumping with a relay at 48v from the entire bank....... be warned that setup gave every electronics guy he ever talked to heart burn and probably cramps, but it did work.....

[ricksure]

Hi Ed.

Sorry I don't have any ideas for you but always interested in your projects!

About your home heating, hows that cavitation heat pump working?

[windstuffnow]

  I wasn't real happy with the overall efficiency of the cavatation heater.  I'm still searching for a good alternative... any suggestions?

  I primarily use wood to heat my house with, it has it's drawbacks... handling, ash removal, cleaning the chimney etc.  There has to be a way to heat without oil/fuel or wood that would be clean as well as non-costly....

.

[rossw]

Well, it might seem to work.

It might even work in practice for you for a while.

But it's fraught with dangers! I won't try to talk you out of it,  but I will point out a few of the reasons I wouldn't do it on anything of my own!

Firstly, no two batteries can be assumed to be identical. As they age, the differences becomes more pronounced and the effects they will cause in this application becomes more difficult to predict.

In a series string such as you suggest, with 6 x 12V batteries in series (or 12 x 6V in series) it is inevitable that one battery will fail before the others. It's a 17% chance that the one you are monitoring will be the one to fail. (ergo, a 83% chance it will be one of the others that fails!)

Lets take two "failure" scenarios.

1. A cell fails open-circuit

2. A cell fails short-circuit.

In a 12V battery, situation (2) will mean you get a nominal 10V from the battery.

Each of these two failures could occur in one of two places:

A. Your refernce battery.

B. The rest of your string.

We also have a 3rd condition to consider:

i. Charging

ii. Discharging

So we have 2*2*2 = 8 possible conditions. Some are safe, some are not.

- 1Ai - if your reference bat goes open, and you are charging, you will measure full voltage (72+ volts) and will immediately go into dump mode (and/or blow up your controller!)

- 1Aii - open circuit discharging, you will apply *REVERSE* bias to your controller to the tune of approx (72-12) = 60V (probably enough to blow up the controller)

- 2Ai - short circuit cell while charging, you will never see a high enough voltage across the reference battery to consider the whole string "charged" and will keep pumping amps in and cook the rest of your string!

- 2Aii - short under discharge - probably the least dramatic. Slightly low output volts.

- 1Bi - open somewhere else under charging - you have no load for your generator, turbine overspeeding, dumpload won't help you because it won't see the high voltage.

- 1Bii - open elsewhere while discharging - no output.

- 2Bi  - short elsewhere while charging - you see slightly higher voltage across your reference battery, ending charge and dumping load a little early. No serious damage, but chronic under-charging of the whole string.

- 2Bii - short elsewhere while discharging, same as 2Aii.

There are a number of "intermediate" situations of course - a cell may start to go high resistance before it goes open, so you can get "partial" variants of the above.

RossW

[RogerAS]

[terry5732]

Just come off the full 72V bank and drop it with a suitable resistor to 12V before the controller

[dnix71]

According to several sites the Outback MX60 will accept a 72 volt nominal array, as long as you step down the output voltage and don't exceed 140 Voc.

http://books.google.com/books?id=im-No5TYyy8C&pg=PA156&lpg=PA156&dq=72+volt+charge+contr
oller&source=web&ots=EjfLKbDaNP&sig=Bp3Bzs5IO_7-vJaImEhUwZlDCJI&hl=en&sa=X&o
i=book_result&resnum=10&ct=result

If you stepped down to 36 volts, you could run two sets of charging wires and tap out the battery pack in the middle.

[windstuffnow]

  Thanks for the insight Ross, It sure sounded like a good way to overcome the obsticles of 72volt charging but when you say it like that it opens the eyes a bit.  

  What about the option of monitoring 48 volts of the bank?  That is about as big a controller as they sell right now.   That still leaves 2 batteries un-monitored but reduces the possibilities a bit for problems.  There is a battery monitor for EV's that connects to each battery, this gives you a look at every battery in the pack.   Called a PakTrakr.  This would give you a visual indication of any one battery going bad... as long as you were there to monitor it.  

  What, if any, would be a good alternative?  

  My second option would be a small battery bank ( 48 volts ) through an inverter to run an onboard battery charger.  Not as efficient converting from one to another and back.  Still a manual effort would be needed to make sure you didn't kill the 48volt bank while charging the 72volt bank in low wind or sun conditions.  

  I suppose, which would be to simple, would be to increase the size of my existing system and charge the car from the main inverter through the on board charger.  Still not very efficient but functional....

.

[windstuffnow]

Would that actually work properly?  It sounds to simple...  

[Jerry]

Hi Ed.

A littel off topic here. But speaking of EVs. How is your S-10 conversion comming?

I drove my  85 Ford Ranger conversion to work yesterday. First time in about a year.

Just about the time of the fire at my store the Ranger quit running. Now normaly these things will run a Zilion miles without problems.

The problem was caused by my first battery bank. 2 things caused the problem. 1 missmatched used batteries and the steel retainer accross the top of the batteries.

While charging over night a small amount of arching between the battery post and the steel hold down strap caused the hydrogen gas to explode that battery. It dumped acid on the brush section of the motor. 6 months later the motor just quit running.

I've rebuilt that motor as good as new, with new batteries and battery rack with acid proof diversion drip tray.

I've also added forced air cooling for the motor and the Curtice speed control.

My on board pulse charger is still working great.

So far top speed around 70 mph. Easy driving nets about 50 miles per charge. Grid power bill for charging for a mounth $20 as a daily driver.

I'm very glad to have this littel very usfull truck back on the road.

Sorry about hijacking your post but I'm exited and quirius how your EV is doing.

PS by EV is 120 volt. If I did it again I'd go 144 volt to 156 volt.

                          JK TAS Jerry

[terry5732]

I think somewhere around 0.01 to 0.02 ohms with a higher value pot in there for fine adjustment. I don't think you need much current for the controller or to fire the IGBTs. Play around with a DVM and some resistors with a small load like some LEDs.

[bob g]

might be you could use a bank of dpst relays so that you could sense the voltage on

the batteries in a stepped fashion.

step one = battery one

step two = battery two

etc.

some form of stepper to switch through each relay, either daily, hourly or whatever

could even be done with a timer setup

bob g

[bob g]

might be you could use a bank of dpst relays so that you could sense the voltage on

the batteries in a stepped fashion.

step one = battery one

step two = battery two

etc.

some form of stepper to switch through each relay, either daily, hourly or whatever

could even be done with a timer setup

bob g

[Flux]

Monitoring one battery is not a good idea. It is probably not a good idea to try to adapt some low voltage controller unless you have circuit diagrams of it and you understand how it works.

All you need to do is the same as any charge controller does, you take the 72V and use a potential divider ( 2 resistors) to reduce it to a level that you can compare to a fixed reference. Feed the reference and the divided output into some form of comparator that will give you a signal that tells you if the battery is above or below the reference. This signal is then used to control the dump load ( if wind is involved,solar could control the input).

The actual details of doing this may be less straightforward as all the common electronic amplifiers and comparators are restricted to about 36v so you need a simple power supply for them. You can switch the load with a whole range of things. Relays will have to be chosen carefully to have any useful current rating at 72v ( at much above 24v the arc will maintain across the common contact gaps unless you use multiple contacts in series or use special dc relays which are not now common and most likely incredibly expensive. Capacitor/ resistor combinations across the contacts may help and freewheeling diodes across the load resistors may be necessary if they contain a hint of inductance.

Mosfets, transistors, IGBTs can all switch this sort of load better than relays but again you need to have decent drivers and without a bit of knowledge of electronics you might struggle.

You have all the relay and switching problems if you sense from one battery, it simplifies nothing except removing the need to understand a comparator and you have all the problems of sensing from part of a battery string and the inevitability that it will get out of step.

Find an electronically minded friend to build you something it will be far better in the end.

Flux

[ghurd]

I'd love to see the wiring for "two sets of charging wires and tap out the battery pack in the middle."

[ghurd]

Reminds me of how much bad info is on the internet.

I would love to quote the whole thing!

G-

[DamonHD]

G, Outback has something not dissimilar in their datasheet for the MX60...

I wouldn't do it, but...

Rgds

Damon

[tecker]

I've been screwing around charging each battery in the bank with the same source . I think the low impeadance picks them up fast like a auto alt in a car . I ve smoked some  

lm317s and am cookin up some one to one toroids for real isolation under max load and alt power mixing(I'm tring to make toroid cores from .30 mild steel copper coated welding wire ) but each battery has it's own feedback that is a big hole in most ev's got a 36 volt front hub bicycle and am messing with a 13 horse (I dropped the hole RTU off a 5 story with no ill efects to the motor not one of the best demos I've ever done)

[windstuffnow]

  Hi Jerry,  The S10 project was scrapped because of the overall weight.  I ended up selling off the S10 conversion parts to fund this project.  I still have the S10 donar vehicle which is a good running little truck but it will be for sale soon.  

  I was inspired by some of the 3 wheel reverse trikes being built from motorcycles, light weight, strong and much safer than a motorcycle.  I didn't need all the weight to run around doing my normal daily items and so much energy was being wasted just carting around the weight.  

  6 weeks into the project I'm just about done building the Trike and it will weigh in at less than 1100 lbs including driver and battery pack.  I had to go with some 75Ah 12 volt Optima's so the range will still be 50 to 60 miles depending on how I drive it which is far more than I will need to handle my daily running.

  Now my problem is how to charge it using solar/wind only ( without breaking the bank )...

.

[Bruce S]

Ed;

   Not sure how well this will work for you, but..

Down in the NiCd and NiMh world , we use seperate charge controllers for each 12Volt bank.

I'm certain our 36 & 72Ahr sets are no where near your needs, but in the past we had the same problem.

Above the 36Vdc mark it was at the time, was very hard to find charge controllers for the entire 48Vdc bank. Somewhat easy to find 48Vdc around 10Ahr banks of newer larger bikes but they tend to need beefing up to handle anything above 12Ahr.

Our solution was to build 12V banks with isolation from each bank for charging; then series connection during usage.

To date I've not seen any problems, this is going on 1 year's work for the last bank built. Granted when this last set was built, extra attention was taken to match the 12V banks as well as the complete set.

I know it's not the 500Ahr area , but might be a different route for a solution.

Cheers

Bruce S

[bob g]

Flux:

my thought on the use of relays had nothing to do with charging current delivery

what i had in mind was the use of relays to isolate a single battery to provide

a reference voltage to be brought back out to whatever controller one wants to use.

not at all different than what takes place with a common ignition switch in an automobile where the switch contacts connect the battery to the sense line of the regulator, but in this case the ability to sample each of the 6 batteries seperately, and sequencially.

as for DC relays as used for sampling, there really is very little current capacity needed, and arcing should not be a problem.

also it is possible at least with a windgenerator, to bring in AC power and switch

it before a rectifier which reduces cost of the relays, if one wanted to actually charge through a relay?

i have found many DC contactors/relays on ebay at very good prices, getting double break contactors reduces the arcing as you stated.

bob g

[boB]

This may not be high enough voltage for a 72 volt nominal battery,

but the MX60 can be brought up to 80 VDC on the battery side.  At least

it used to be able to go that high.  Don't know if they've changed that

original limit.

boB

[windstuffnow]

Thanks all for your thoughts and ideas.  With as much money invested in batteries, I'd feel better knowing they were going to be taken care of.  So I'll probably absorb the losses, increase the size of my system and use the onboard charger through my existing inverter.

I was really looking forward to building a HV wind genny though.  I have a few ideas on shorting the AC side of the turbine when the batteries are charged, so it's still on the table of ideas.

.

[dnix71]

This is what I had in mind. It requires an isolation diode.

[boB]

This has been done MANY times with two MX60s and two 60 volt battery's in series for

a 120 VDC battery bank.

You have to remove the "top" MX60's MOVs though, since they connect between negative/postive and GND. When that is done, the two MX60 grounds can then

be connected together.  The reason for this is that the MOVs are 200 Volts

and two 72 Volt arrays in series would be over 200 Volts DC.

boB

[ghurd]

Notice the diode is shorting out 36V.

The anode has 36V+, the cathode is ground, and smoke will come out of something.

G-

[dnix71]

Yep.

My first drawing had a knife switch where the diode was. If this was an EV, then you wouldn't be driving it while charging. Our emergency genset at work has a 24v start. We had 2 24v float chargers fail and had to resort to using a car battery charger that way to recover the two 12v batteries enough to start the generator. The second time the batteries went dead it ruined them, but so far the repalcements (and the third float charger) have held.

[oztules]

Hi Ed, just built this to help another member out. It is a simple but accurate dump controller.

It is simple to build and this one with these values covers from 64v to 100v in 0.1 volt steps. Hysteresis is adjustable from 0 to 2 volts and beyond.

It would drive an npn darlington or n fet  to turn on a small relay. This could then turn on aux starter style relays from industrial machinery ... fork lifts, floor scrubbers. These relays are from 36 to 48v @ 150 amps. Use 2 36v ones in series and switch massive dc loads all day long (just like a fork lift in fact). Thats if you want to switch high current DC at higher voltages.

If you can find a place that scraps old floor scrubbers, then you have hit gold. They use heaps of these relays in the clarke, tennant, advance etc floor scrubbing machines.

More desirable would be switching solid state ac relays in the ac line two would be needed for three phase.

more on this dump is from here:

http://www.fieldlines.com/story/2008/6/27/481/71619

Best of luck. I don't understand the negativity surrounding a very simple question with a very simple answer. It really is almost as simple as Terry says.

The dump is simple, the switch gear is simple. Nothing new here.

.........oztules

[windstuffnow]

Thanks Oz, I may give it a try... I really don't have much experience in electronics, finding the parts is quite a challenge for me in itself.  I tend to make more smoke than working devices although if the instructions are clear enough I've done some pretty exceptional things.  ( patting myself on the back for the ones that did work and some of the kits I've purchased and assembled ).

.

[bob g]

Ed:

a very interesting and timely project you have going on there

how about some pics?

over the years i too have kicked around the reverse 3wheeler concept too, and windcharged/electric primer mover is an awesome idea!

look forward to seeing the results

bob g

[Matrix1000]

Anything close to this?

[Matrix1000]

Or this?

If someone would just make these damn things instead of just design em I'd buy one tomorrow. I'd love to put some solar/wind into them to make the 40 mile drive to work and back every day rather than pay the Saudi's for burning their black tar juice.

!

I wonder if any of us could put toghether some homegrown 'motors' to power our EV's