different batteries

[sandovalch]

I would like to know if someone could help me with this:

Now I have 6 marine batteries (100Ah) connected in parallel for a 12V system. I would like to expand and add 6 more batteries, but the ones I'm looking at are Trojans T-105 (6V), 2 in series for 12V. Can I mix these to types of batteries or will I be likely getting some charging problems? I use a Trace C-35 charge controller.

[nothing to lose]

I can't recall the correct answer exactly why to not mix them but it's been mentioned alot and searching the site for things like "mixing batteries" or "adding new batteries" should provide lots of previous posts with answers.

First few things I can think of off hand are if your currant batteries are older they may drag down the whole system with lower performance. Not recomennded to mix new and old normally.

Different types and amp hours. Don't know about a T-105 but my Trojans(L-16 I think) are 360amphrs. Mixing 360 and 100 amp hr batteries will probably drop perfornance alot and also perhaps make proper charging difficult. Over charge the smaller ones or cause the larger ones to never fully charge?

Self discharge rates also have an effect. As I recall older batteries may self discharge more than new ones. Also battery size, I think it's been said about 1% self discharge rate. So 100amphr would be 1 amp per day but a 360amp hour would be 3.6 amps per day.

In general mixing is not good but you gotta do what you gotta do.

I wire up alot of things for fast temporary use so sometimes I do forget the diffence between what works ok and what is best. Like now I am transporting high amp trojans battery bank in my truck and charging at home then using those at a remote location to charge a smaller battery bank. This works ok but of course is not best, but I have no charging source at the remote location at all and it's better than running a genny.

[pyrocasto]

Would it be possable to run a cable from the genny/panel, to each batter bank, and use a diode to stop them from back flowing into each other? That seems like it should charge both systems, but one wont drag down the other. One problem with that though, is you can only use one at a time that way. You could use two different inverters, or just have a switch.

Just a thought.

[nothing to lose]

That would probably work. Another thing, probably the basic same thing in a fancy box, to charge 2 battery banks at once seperatly from the same power source you can get a battery isolater from Autozone (and many other places). You know like to have one battery for starting a vehicle and a bank to use for camping or tools, niether bank will drain the other when it gets low but both are charged when the engine is running. I think I saw one for around $25 recently at autozone.

I never actaully saw inside one to see how they are made. I suspect something simple like just splitting the power feed cable into two lines each with a blocking diode so neither battery knows the other is there. But then I question if that's it then how is the charging from the altenater regulated? It would seem to me off hand with a blocking diode type setup a charging source like altenator regulater would not know if the battery was at 11V or 13V since the feed back is blocked.

My question though is with all the fancy gizmo's for charging that supposedly read a batteries condition and adjusts for it what will happen with blocking diodes in the line. Surely something like a smart charger would not even turn on. Unless the charger is only reading it's own output somehow to determine how much the battery will take.

I have both a smart charger (vector) and a booster (maybe vector) and neither will do anything unless connected to a battery with some juice in it. Totally dead battery these things won't even start up. I think a blocking diode here would have the effect of not letting them startup as they would not see the battery at all.

I don't know how a trace controller controls the charging or anything else it may do like dumploads when batteries are charged, so I don't know if diodes or one of those isolaters would actually work with it correctly.

If charging is not a problem using the above, then I would think using one cable into the battery bank for charging and a seperate cable out to the inverter also with blocking diodes would alough both banks to be used on one inverter at the same time.

The cables from the battery bank to the inverter being only one direction, power out, the batteries again should not see each other, but the inverter will be drawing from both banks at the same time and if one bank goes dead then it just draws all the power it needs from the one still having power.

Put some thought into it, somethimes the answers just pop right into your head from no-where. As I was posting this I realised I was planning to something very dumb myself! Hows this for dumbness??

I have been charging a bank at home from the grid, taking to a remote house and running a small inverter in the truck to power a charger to charge those. This works well for now, but I am playing catch up all the time because the big inverter is running from the ones I am trying to charge at the same time. So I was planning to set up heavy cables (don't have long/heavy enough ones yet) and such to run the large remote inverter directly off the truck bank and disconnect the remote house bank and use the small inverter and charger to charge those also from the trucks bank. This way I am not using power from them at the house as I am charging them. They will get a fuller charge and I can more fully drain the ones on the truck. Sounds good?

 DUMB DUMB, I just realised!!

I would be running a 5,000watt inverter at about 500-1000watts or so, something small anyway most of the time. The small inverter only powers my charger up to 20 amps, it's a 40amp charger though. Ya, duh on me! Why not just forget the small inverter on the truck, why run 2 inverters? One is barely being used the other maxed out and still not enough! Just run the 5K inverter off the truck, battery charger from that, charge the remote bank at the full 40 amps!! 1 inverter running a heavier load and 40amp charging is much better than runnning 2 inverters and only getting 20amp charging!!

 I only do it because I need power there and no way to make it near by, I don't own that place so limited to what I can build or change or install (working on it though). Nothing is really great, but boy was I planning something really dumb as for the 2 inverters!!!

Anyway I was going to look for blocking diodes myself and see what I need for the power I would be drawing at that location so I could have both banks wired to the inverter, neither knowing the other was there, then just disconnect whichever set needed disconnected at the time. Sort of a oneway wire, power into the inverter from both/either banks but any wire would be dead when disconnected from a battery bank. No back feed through it from the other bank. Eliminate some manual switches and chances for error this way.

[sandovalch]

Thanks for the info.

I think the charge controller senses the battery voltage all the time and regulates the AMPs to the batteries when the batteries are near fully charged. If I put a diode between the charge controller and the batteries, it won't be able to do that. So it would most likely overcharge the batteries.

How do I get info on charging voltages for different battery types? I think the best would be to buy batteries for a similar charging voltage but higher AMPs or is there a relationship between charging capacity and charging voltage?

[alcul8r]

I've seen lots of times where you should not mix batteries, but the batteries I'm using come from people who are replacing whole strings instead of a single battery. I would never put a 200AH abttery in series with a 100AH, but I see no reason not to put them in parallel.

Do not put diodes between batteries and charge controller.  In many cases the battery powers the controller.  Also the voltage drop over the diode will affect charging.  Make sure your batteries are in good shape.  I'd use a pulser on them, but I have a 24 volt system, so it is easier for me to put it over 12 volts without trying to pulse the whole system at once as you would be.

Rex

[pyrocasto]

That's right, so I guess you would have to get two CC's or something. Cheap to build yourself, if you're good with electronics.

[ghurd]

I don't see a huge problem with mixing them in your case. The batteries are the same chemistry type, so charging shouldn't be much of a problem.

The marine batteries are nearly new (?), so the T-105 should be also.

Maybe it is not the best way to go, but what are the options? Buy all new batteries?

You gotta do what you gotta do.

G-

[TomW]

Folks;

I agree with Ghurd here. In an ideal situation you would use batteries of the same type, size and age but if the opportunity arises to put together an odd combination on the cheap it will probably work fine for the cost involved.

An oddball combination of batteries will work a LOT better than no batteries. Simply keep an eye on them to be sure they play well together.

Cheers.

TomW

[whatsnext]

I'm going to jump in with Ghurd and TomW here. As long as the chemistry is the same in all your batteries they should charge and discharge together just fine. This would be a very good time to learn how to take VERY accurate specific gravity readings. Let us know how it works out for you.

John............