Batteries and Isolation

the_experience03

the_experience03

Senior Member
Joined
Feb 16, 2006
Posts
2,669
Location
Saint James, MN
Now that Havoc's floor is done and we've finished doing all our measuring and laying out of the floor, it's time to start thinking seriously about how exactly all the systems are going to work.

I plan to put the batteries in the compartment currently occupied by my webasto heater (it will be on eBay unless someone here is interested in it) and possibly even putting two more in the starting battery compartment (they are adjacent) depending on space availablity and the battery type I end up going with.

I'm a little torn as to what type of battery I will be going with. I know all the advantages of this type and that type and would like to get the best money can buy, but I will hopefully be starting a new job here shortly at a place that sells marine type deep cycles and if my employee discount is enough, it might be worthwhile buying those instead of something more expensive.

I've been toying and toying with how to go about isolating the house and starting batteries in the cheapest, most effective way. I stumbled on this idea almost by accident while I was shopping for golf cart batteries. My plan is to keep everything (alternator, other wiring) hooked up to the stock battery as it is now. I will then run a positive and negative jumper wire across to my battery bank to tie them together, but on the positive side I will install an electric golf cart solenoid. These things are rated for 200+ amps with a 100% duty cycle.

The solenoid will run up to a switch on my dash panel that hooks into the ignition-switched "J-block" on the bus. In this way the starting battery will ALWAYS be isolated with the ignition off. If I leave the switch on it will automatically start charging the house batteries whenever the engine is on or will allow for jumping the starting battery or boosting it on those really cold Minnesota mornings. I can also still isolate the house batteries when the engine is running to give the alternator a chance to cool or to allow full charing power to the starting battery on after an extended crank.

This isolation system will also allow me to use my Craftsman lawn tractor turned alternator/generator to charge the house batteries without any feedback into the main electrical system should I ever finish that thing.

Best of all is the price....about $25 for the solenoid.

Can anyone see anything wrong with this idea? Also, what are people using for terminal blocks, etc to tie their batteries together in parallel? I have a lot of stereo equipment type stuff, but that seems rather expensive.
 
I have had very poor luck getting my house batteries to charge properly just by connecting them in paralell with the starting battery while driving. It seemed to me that it should work just fine, but in practice it was less than stellor.

Buying a battery isolator that is rated for the amperage of your alternator is not the cheapest solution, but it works well. I had an isolator on my old bus, and ended up replacing the alternator soon afterwards...were the two related? or did the alternator just decide that it had enough after 254K miles? IDK

Another solution is to have an invertor connected to your starting batteries that can run a charger. Maybe a 30 or 40 amp smart charger. This is not very efficient, but it would work fine. Drawing more amps from your alternator on a skoolie while driving will not affect fuel economy (not enough that you would notice at least)
 
I'm glad you said something about the charging rate when the house and starting batteries are connected in parallel. Another option I have available using the same concept as before is to use a solenoid designed for the forward-reverse function on a cart. It's the same idea as before except that the solenoid would be placed on the positive cable off the alternator. It is designed so you can switch one output or the other on. This way I could take my pick between which battery gets charged. Unfortunately this means that one or the other won't be getting charged going down the road as well. I'm not sure I care for that idea.

I'm going to Arrowhead Battery and Golf Cart tomorrow to figure out how many batteries of what type I'm going to want as well as how much they will cost. Peter Zunich knows his stuff and won't steer me wrong so perhaps I'll ask him what he thinks I should do.


You're right that it's a little odd that hooking the house batteries in parallel doesn't work as this is essentially what a charger or jump starting is doing....oh well....

One other idea...what if I put the solenoid off the alternator output (i.e. split the wire with a distribution block) and put hte solenoid on the house battery leg of it. Is there any reason why **** wouldn't work?
 
I ran a sure power isolator for a bit with no apparnet problems. Then I got a loarger (100 amp) alternator which exceeded the isolator's capacity (70 amp). So I opted for a simple solonoid. It takes incoming power for the alternator and distributes it to two outputs (starting and deep battery banks) when a switch is turned on. I wired it to an empty slot in my fuse box which turns on with the ignition. So the solonoid allows power to flow to the batteries when the switch is on, then stops the flow when the switch is off. It's simple and does not have the same issue's that isolators have. It cost about $40 at Napa.

On a side note, at the RV dealership where I work, we don't coarry or sell isolators because of the problems they have caused clients. I will double check monday what those problems were (other than robbing volatge).

-Richard
 
another option, especially if you don't have air brakes is to add a 2nd alternator just to charge the house batteries. If you used a standard GM 65? amp alternator, they're like $35 bucks if you have a core. I don't know how long it would last, as it would often be working at maximum output. An alternator is really designed to put all of it's energy into the battery until it comes up to full charge 13.6 volts (or a lil higher) while it's charging. Not haveing an air compressor would leave lots of room to mount the alternator.

if you use a 130 or 200 amp skoolie alternator to charge deaad batteries, it seems that pounding the battery with that much current as it goes from dead to full charge would reduce the battery life.

60 amps into 2 pair of 220 amp hour batteries would be on the high end of acceptable i think.

do they make a cheap charge controller what would only allow 20 or 30 amps to flow during charging?
 
Sounds to me as if your describing a standard RV setup used in the 70's (my 78 winnebago uses it). Here is a link to a standard constant duty solinoid with a diagram (link) of how it is connected. http://www.tekonsha.com/teabatswitch.html
Your dash switch (basically the same as my dual/norm/MOM dash switch) would allow manual control of the relay. If the dash switch power was from the ignition switch then no power when key is off.
3 pole relay used when mounting to chassis metal (case ground). 4 pole relay used for wood/fiberglass mounting.

Dave
 
The second alternator idea is kind of what I'm talking about with my old lawn tractor. I'd rather fuel a 12 horse briggs for 4 hours than a 6.6 diesel. I do have airbrakes, but there would be enough room under the hood to fit another alternator. I just don't want to :LOL:

As for the small versus big alternator....alternators really should only be charging a bank with an amp hour capacity of four times their output according to the guys at Arrowhead Battery so the 60 amp alternator would be a less than ideal idea. Of course for the price of getting one rewound I think it might be worthwhile...10SI Delco alternators are neither rare nor expensive. Of course with 12 hp available I'd like to turn something a little bigger.....

All that aside...I still need to isolate the house batteries from the starting battery. Perhaps I just need to ponder this a little more as I really don't want to buy an isolator that can support the 200 amps my alternator can put out. BTW...you can get a digital style coltage regulator for an alternator, but they're $$$ and still not perhaps the best solution.
 
I didn't realize you were trying to create electricity while parked. (not that you can really "create" electricity)

My recomendation is to spend the 900 bucks on a honda eu2000 geni. The fuel savings alone will pay for the geni after a few years. Not to mention it's so quiet compared to a regualr 12 hp engine. You can easily get 15 hours per gallon from the honda, you'll prob suck down at least 1/2 gallon per hour with the 12 hp motor.
 
my 84 crown uses 4 batteries in paralel. + to +. _ to _ twelve volt. it has a isolator switch (factory) on the wall of the engine bay, drivers side. the isolater is a round BIG knob looking thing. i have seen the same isolater knob on some gillnet fishing boats. it has a off- bank1-bank2 and both.when i start the bus i always use the BOTH setting. but when i stop i rotate between bank 1 and bank 2 to run a 9 inch ac /dc color t.v. and a police scanner and my cb radio. i dont have all that much to run and i usually only run it for a couple 3 hours or so.
 
See here's the thing, Jason....I'm on a college budget and the 12 horse is free and works great. I have a 2300 watt 1960 something Briggs generator that runs GREAT, but if I use that for charging it doesn't leave much else left and it's not exactly quiet.

The reason I want to isolation is both for when I'm parked and when I'm driving. I'm not opposed to using the alternator on the bus for charging the batteries when I'm stopped if the need arises. My homemade alternator-generator thing is low priority right now. Most of all I just want to get the bus ready to go for this summer.

I probably should just breakdown and buy a diode type isolator. I just don't like the idea of paying a decent chunk of change for something with so many compromises.
 
Small engine 12VDC generators are not new (I have built one). Google the net and you will find sites like:
http://theepicenter.com/tow082099.html
http://www.green-trust.org/equipment.htm

If one wants to dig into batteries and charging I would start at
http://bart.ccis.com/home/mnemeth/12volt/12volt.htm
Just remember that this can be a very large subject that has many answers depending on your own situation. Given the price of batteries though, it is worth getting familure with. You will also discover that there are many many view points about this subject.

Dave
 
My isolator is a switch between the starting battery pos. and the house battery pos. (that are in parrallel) I can reach it from the driver's seat. Turn it on, all batteries are charged by alternator. Turn it off, only draw from house batteries so as not to drain starting batt. Cheap, effective.
 
You have no problems getting the house batteries to charge in parallel like that? I still can't see any reason why it wouldn't work, but electricity hardly ever follows the laws of physics like it should.....there's a reason why I chose mechanical engineering instead of that electrical crap.
 
I felt the same way

I felt the same way about those darn flowing electrons untill I realized all the formulas were basically simplified flow thru tubes. once I converted all the variables into fluid dynamics I was able to understand most of what was going on then convert it all back again to get the right answer on the test
 
I try the same thing and it works great on paper. Where I run into problem is in the real world :LOL:

In theory the batteries in parallel would be just like two pipes in parallel. Overall mass flow rate would be the total number of amps supplied by the alternator and the individual mass flow rates would be determined by the draw from each battery bank :?: Either way...the total mass flow rate would have to be equal so the volumetric flow rate would be lower on each one taking more time to charge due to the lower velocity of the "fluid"....blah blah blah....

The problem with this is that some people have expressed that they have trouble getting their house batteries in parallel to charge. On paper it doesn't make sense, but calculations on paper only take you so far :LOL:
 
So far, my batteries charge completely via alternator. However.... I have limited time on the setup and all batteries are new. Performance may decrease over time, I'll have to wait and see, But for now, all is well.
 
I've seen it before in small lithium batteries

I work for NASA on mini UAV's and we have seen this on our aircraft. the rechargeable lithium ion batteries can be hooked up in parallel and work fin in the system but you can't charge them that way we had to remove them and charge them indipendently. the sparkies couldn't sufficiently explain that one to me though.
 
battery charging problems

:idea:
I'll postulate a theory here.
when you have voltage in parallel, current varies. ( ohms law )
now at the beginning of your charging process you have one battery charged or nearly charged, and the other nearly drained.
What will happen is the sensing circuitry in the regulator will determine that not much output is needed because of the higher charged battery and will slow the charge rate considerably. You see this when you jump start a car and only get a "surface" charge.
Now IF you provide to the regulator a voltage sense based on the current status of the lowest charged battery ( which is essentially what an isolater does ) then the isolater will channel the current to the battery that needs it the most and feed some bias back to the more charged battery to test it to see if it now needs charging.

Hope that helps some
 
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