12/24v charging on mill - tapping the brain trust!

[Ljohnsaw]

I put this here in General as I think there might be a larger audience than Milling.

I'm building V.2 bandsaw mill and I've change the lift mechanism.  I am still using a 24v wheelchair motor.  I was using a 20:1 gearbox and lift chains with a 2:1 reduction in the final drive so roughly a 40:1 reduction.  Lift speed was slow but consistent.

Now I am going with a 2:1 reduction to 4 ACME 10 pitch screws.  Haven't done the math but I think the previous chains going over 1" sprockets resulted in a net reduction of something less the 40:1 as the ACME screws are lifting at about half the speed.

So, I could remove the 2:1 reduction but the motor is working pretty hard as it is - don't think there would be enough torque with 12v.  So I think the only option is to go to 24v.  Is there an easy way to maintain two 12v batteries in series and keep them charged with my 12v GM 1-wire alternator?  Is there some new solid state device that would take care of maintaining the charge on both the batteries?

[Tacotodd]

You can always use a battery isolator. From what I've read, they will fully charge 2 12V bats plus never concentrate on the weaker of the two.

Full disclosure: I've never had cause for running one, I can only go with what was on/in the catalogs at my former parts store life.

[Iwawoodwork]

There was a solenoid like device, maybe a Parallel Switch, that was used on older large commercial trucks that switched from 12v to 24 v when starting and allowed the electrical system to operate on 12 v as I recall. Probably some info online about the old system.

[21incher]

I think you can just change out the internal voltage regulator and get 24 volts from a gm 1 wire.

[YellowHammer]

Certainly, it's pretty common technology, typically installed on boats that have house and service batteries, like bass boats and saltwater boats.  I had one on my bass boat, 24V trolling motor, and 12V cranking.  It's a muiltibank battery charger and isolator, which is directly installed to each battery, and charges them all independently and fully off the 12V engine, no matter how they are hooked up to each other.  Battery isolators allows multiple batteries to share a common charging source, while the engine is running, while being independently discharged.  

They are very effective and once installed, are hands off, as long as your alternator has the power to charge them all.

[Ljohnsaw]

OK, I looked up battery isolators.  They state they keep the batteries separated so they can charge independently.  Intended to be used with negative ground (which I have) and NON self energizing alternators (isn't a GM 1 wire self energizing?).  But, I want the batteries connected in series so I can drive the wheelchair motor with 24v.  What am I missing?  Or, rather, what key word(s) need to be in my search to find the right type of isolator?

[mike_belben]

probably wiser to go to a 24v alternator in the long run.  in the short run you can put alligator clips on the alternator output.. one positive and one ground wire to the alt case.  these clips can be moved from one battery to the other in the series array.  

so youve got two batteries oriented  +   -    +    -  

you put the alternator jumpers on only one battery at a time on their proper terminals.  rotate them often. the series array doesnt know that its getting half its volts from an alternator rather than a block of stored voltage.


i have also drawn 12v off just one of the batteries in a 24v series array without any issues yet.

[Ljohnsaw]

My initial thought was to use a DPDT switch to connect the batteries to the alternator to get what you are saying, Mike.  But, I'm pretty sure I'd have to isolate the alternator from ground in that scenario.  OR, be able to break the first battery ground when switching.  Gets complicated real quick trying to make it idiot proof and to carry enough amps for the starter and lift motor.

Going with a 24v alternator I'd be worried about the batteries not being charged equally and causing one to degrade in short order.

On another note:  While waiting for replies, I eliminated the 2:1 chain reduction so directly running the ACME rods.  No noticeable change in the motor speed or sound (pretty stout little monsters!) and the lift speed increased but not quite twice as fast.  Livable but not ideal - still would like 24v.  Working on a idlers sprockets mid-span.  The change droops a little in 5' (sideways) and the little bit of slack causes it to jump a tooth every now and then.

[mike_belben]

Yes your case ground has to always be a case ground on the alternator.  

If you went to 24v charging youd be charging both 12v batts as a single unit, the middle two connections would simply be external instead of internal to the case.  itd be equal charging afaik. 


Ive looked at this a few times and never found something simpler than jumpers to swap charging.  Now if you want a bunch of other stuff on 12v and just one thing on 24v with 12v charging there is a way to do that with a solenoid.  Your second battery stays in isolation and periodically needs a manual charger connection.  Ive done it on a quad for hare scramble cold starts. 

[hedgerow]

If you look up series parallel switch on old 12-24 truck starting running systems they did what you want to do. Charge with 12 volt alt and start on 24 volt. It would be easier to just buy a 24 volt alt. DB electrial has a Delco 10 24 volt alt for eighty bucks. My old cat 941 B track loader has a 24 volt charging and starting system and I run two group 31 batteries on it for 24 volt and never have a battery issue. 

[Hilltop366]

Could run two separate systems if your engine has 12v output, engine output for starting battery, 24v alternator for wheel chair motor battery.


  

[Ljohnsaw]

Soooo - more testing.  Got an idle sprocket/tensoner installed and works better - no pops and bangs.  The lift speed is about 7 or 8 seconds for 1 inch of lift :  About the same going down.  That tells me the motor is not straining too much on lift at 1:1 sprocket ratio.  That is a might slooooowww since I have a full 42" of lift available.  So, I made up a bushing for the big sprocket to fit the motor and now have a 2:1 increase in speed.  I started with just the opposite.  Now my lift speed is about 3 seconds/inch.  I think I can live with that.  Fairly quick but not too quick to bump it to the cut size.

In actual use, I only use the lift while the engine is running so I don't drain the battery that is needed to start the engine.  What I've seen is the increase from a static ~12.9v on the battery to 14.something when the engine is running makes a noticeable difference in the lift.

Thanks for all the input.  I will give this a try (when I finish my re-build) sometime in the next couple of weeks (assuming the snow is gone) and see how it performs in the field.  If I'm not happy with the speed, I'll probably go for the 24v upgrade - perhaps with a 24v GM 1-wire if the regulator is not replaceable.

[mike_belben]

1wire is not great.  Setting up a standard alternator with load sense, output and field is quite easy and works better.