Parallel charging different batteries

Submitted: Friday, Jul 15, 2005 at 13:10
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Hi Chaps and Chappettes,

I have 2 x Delkor Calcium batteies as the main and auxilliary batt in my 105 series landcruiser. I leave the 'fridge in the rear of the l/c and it runs off the aux battery. I have a rotronics MH10 charge isolator thingy that charges ther main battery before hooking them both up in parallel.

Just recently, we purchased a campertrailer that has a couple of AGM (absorbed glass matt) batteries. So far, the only things we run off the campertrailer batteries are low power lights. When the campertrailer is hooked up, its batteries are connected in parallel with the aux battery. As we drive merrily along, all the batteries are connected in parallel as they get charged from the alternator.

I read somewhere (may have been here) that charging AGM batteries and wet cell batteries in parallel is a no-no. However, I cannot find out why this is so and what damage is done to what battery (and over what length of time).

Can anyone enlighten me? I'd like to know so that I can "re-engineer" my setup without spending unecessary $$$$'s. Any suggestions on layout would be appreciated.

Kind regards
Stephen J.
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Reply By: Mad Dog (Australia) - Friday, Jul 15, 2005 at 13:30

Friday, Jul 15, 2005 at 13:30
I've read this also Stephen but have no idea why but number of people do it quite successfully it seems. Actually to be technically pure all batteries in parallel should be identical including the age.
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Follow Up By: Member - Stephen (WA) - Sunday, Jul 17, 2005 at 19:23

Sunday, Jul 17, 2005 at 19:23
Thanks Mad Dog,

I haven't had any trouble with my complete set-up (though I've only done a couple of trips like it is at the moment). I just wanted to make sure I wasn't buggering too much up by paralleling my AGM and Calcium batteries.

Ta
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Reply By: hl - Friday, Jul 15, 2005 at 13:42

Friday, Jul 15, 2005 at 13:42
The AGM batteries my need a slightly higher voltage to reach full charge...
However, since you normally cannot adjust the regulator in modern cars, it won't matter anyway. It certainly won't do any damage to any battery. Just connect your AGM's to a mains powered charger to top them off whenever it is convenient.
Cheers
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Follow Up By: Member - Jeff M (WA) - Friday, Jul 15, 2005 at 13:46

Friday, Jul 15, 2005 at 13:46
Yeah, pretty much agree, I would also charge my calcium's off 240v once a month or so anyway because they won't get a full charge of the car either, that's what I do with my two calcium's. (similar config to yours).
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Follow Up By: Photoman - Friday, Jul 15, 2005 at 15:29

Friday, Jul 15, 2005 at 15:29
I'd just like to make a little correction with out wanting to step on hl's toes. AGM batteries actualy have a lower internal resistance and therefor will charge at lower voltages. in theory this lower resistance in the AGM could cause cause charging problems for the the wet batt.

side note
AGM batt are perfect for trailers because of the ability to charge close to 100% at lower voltages, this compancates for the voltage drop which U will get running wire plugs etc all the way to a trailer.

I'd do a little more research before charging them in parral- with wets, it wiil probable stuff the wed batt over time through under charging... Remember "Batterys rarely die - They are murdered by bad charging technics!!!!.

My 2cents worth
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Follow Up By: Member - Jeff M (WA) - Friday, Jul 15, 2005 at 15:36

Friday, Jul 15, 2005 at 15:36
Yeah good point, however I think you'll find the Calcium-Calcium batteries he's using up front also have a lower resitance to your typical lead-acid wet cell, not as bigger diff as the AGM but with load (like headlights, fridge and that long old cable back along the vehicle to the camper you'll probally find the voltage drop alone will sort out the charge voltage diff.

Would be interesting to set the rig up as if you were going away and stick a multimeter on the leads going onto the AGM's, I reckon (depending on the type of cable etc) you'd probally have at the very least a 0.2v drop.
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Follow Up By: Photoman - Friday, Jul 15, 2005 at 15:52

Friday, Jul 15, 2005 at 15:52
Ha ya Jeff,
I'd love to know the result, I'm in the process of modifing the electrics on my CampO and have thought avout this same setup, but I'm reluctent to spend the bux on that much 10mm-sq cable ro set it all up properly only to find I keep suffing my Aux batt in the car. Ideal settup would be AGM batt in for main an aux in car + AGMs in trailer, but with 1.5 babies at the moment a can't go spending $800+ on Batts at the moment

AGM batts look like being a great batt in all applications (main & aux) and I've done a bit of interesting reading on the actuall AmpHrs avalibale from AGM compaired to wets and deap cycle. seam the dispite pop opion deep cyc batts should not go below 50% charge, whereas AGM can be run down to about 20 - 30% charge ie your 100 amp AGM battery has a lot mor power avalible than 100amp deep cycle

2+2=4 cents worth
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Follow Up By: Member - Jeff M (WA) - Friday, Jul 15, 2005 at 16:08

Friday, Jul 15, 2005 at 16:08
"with 1.5 babies at the moment a can't go spending $800+ on Batts at the moment "
LMAO! Tell me about it!!
The other option would be to put a small regulator in the trailer that would drop the voltage a specific amount, you can buy kit from Jaycar pretty cheaply. You would need to make sure it can handle the amps the AGM's going to suck through it though.
AGM's are probally the go, but can't afford them. I've given these Calcium's a go to see how they work, seems to be a kind of half way house beteen Lead-Acid and AGM.
Took them away for the first time last weekend and found them to be excellent, it was minus temps and everything ran like clock work, within 5 minutes of starting the car and it only idling (warming up) the volt display was already display 14.0V The old wetcell DS used to struggle charging at about 13.3v.
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Follow Up By: Member - Stephen (WA) - Sunday, Jul 17, 2005 at 20:01

Sunday, Jul 17, 2005 at 20:01
HL, Jeff and Photoman,

Thanks for your thoughts.

I currently charge all the batteries with a spunky 3 stage charger I picked up some time ago (15 Amp jobbie from Projecta) before I head off on a trip. The campertrailer has its own charger as well.

When we are away, I take any opportunity to charge everything up individually from 240 as well (if we happen to stop at a caravan park at any time).

I also charge everything up individually after a trip as well.

We don't take a generator away with us at all, so apart from the 240V charging regime above; the only re-supply the batteries get is from the vehicle altenator.

Our trips tend to fall into the "drive for a day and stop for a day or two" sort of routine; so the batteries get a fair bit of charging from the alternator. We haven't had any probs thus far but we've only done a couple of trips with the new campertrailer and I wanted to make sure that I wasn't going to bugger some expensive batteries with my set-up.

Kind regards to you gentlemen,
Stephen J.
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Reply By: Member - Brian R (VIC) - Friday, Jul 15, 2005 at 15:34

Friday, Jul 15, 2005 at 15:34
The charge voltage set points for gel cells is different to flooded lead acid batteries and they are a little different to AGM batteries. AGMs are able to absorb charge at a very high rate I understand care needs to be taken charging them in parallel with flooded lead acid batteries (although I was planning to do the same myself until your query made me look deeper into it). It is quite unsuitable to charge gel cells along with AGM or lead acid. Here's an informative link for further reading: http://www.vonwentzel.net/Battery/01.Type/index.html

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Follow Up By: Member - Jeff M (WA) - Friday, Jul 15, 2005 at 16:02

Friday, Jul 15, 2005 at 16:02
People running those jump starter packs are doing it all the time, they use 7 or 14amp/hr Gel cells normally. I spose it's on a smaller scale though...
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Follow Up By: hl - Friday, Jul 15, 2005 at 16:04

Friday, Jul 15, 2005 at 16:04
Well,

I just have to pull out my toes from under your foot.....
The maximum charging current is actually limited by what the alternator can supply. If your battery has a lower internal resistance than others in the same circuit, it will take a little more current initially, but once all batteries approach full charge, they will not take a lot of current and the resistance of your lead going back to the van becomes insignificant. It does not matter what sort of batteries are connected, the regulated voltage form the alternator stays the same and it is that voltage alone that determines whether you can fully charge or not. Most regulators seem to put out between 13.9 and 14.5 volts (it also varies a bit with temperature).
I should also mention that the difference between a full charge achieved with a mains charger over say 24 hours and the charge from the vehicle system is probably only 10%, so it is hardly worth worrying about.
Cheers
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Follow Up By: Member - Jeff M (WA) - Friday, Jul 15, 2005 at 16:21

Friday, Jul 15, 2005 at 16:21
"I should also mention that the difference between a full charge achieved with a mains charger over say 24 hours and the charge from the vehicle system is probably only 10%, so it is hardly worth worrying about. "

Sorry if you feel I stept on your toes, it was not my intention, however;
If you do not fully charge your leadacid battery it will start to sulfate
decreasing it's capcity for future charges.

You are correct in that a battery will only take as much current draw as it requires from the system/circut but I believe the concern being stated above is voltage related, if the gell cell starts to gas from being charged at to higher voltage it will be permantally damaged. A Lead acid can be topped up with water. Conversly to fully charge a Deep Cycle battery it needs to be taken to 14.5V. I don't know what new cars are like, but mine with NO LOAD can only get to 14.2V MAX (it very rarley does, normally about 13.9V).
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Follow Up By: Photoman - Friday, Jul 15, 2005 at 16:28

Friday, Jul 15, 2005 at 16:28
hl - hope you've got your steel caps on!!!!

Theres a lot of variables here hl, first Alt my put out 13.9 to 14.5 volts but the voltage drop over the distant to the trailer will vary depending on distance, the amount of copper in the cable, types and number of conectors etc etc. if the voltage at the the trailer batt clamps is only sa 12.5 volts it will be impossible to fully charge the batt. Remember batts are not flat a 0 volts but at 11.5volt a auto batt is considered flat!

Re 240 volt charger - many "auto chargers" will do a worse job of charging a batt than your Alt. any a 3 stage charger or an advanced Solar Regulator will bring a battery up to full charge, good chargers start at about $300, the arlec for $39 to $99 belongs in the bin, if used regularly they will "murder" deepcycle batt. The only use for them is getting enough oopf in a cranking batt to start the car.

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Follow Up By: Member - Jeff M (WA) - Friday, Jul 15, 2005 at 16:40

Friday, Jul 15, 2005 at 16:40
" 240 volt charger - many "auto chargers" will do a worse job of charging a batt than your Alt. any a 3 stage charger or an advanced Solar Regulator will bring a battery up to full charge, good chargers start at about $300"
Yeah they are not ideal, however if you use them properly (carfully) they can work.
I use a cheapo 8amp charger, I run it until the the Voltage is at 14.5v then turn it off. (rest) then trickle it up to about 13.5v then turn it off. That's essentially what a 3 stage is doing anyway, except you can leave the 3 stage on for as long as you like as it will keep cycling. You can also buy a Jaycar kit that monitor the voltage and automatically turns the charge on and off for about $30 bucks. Sure not as good as a real 3 stage but better than killing your bat's and some people can't afford $300! ;-)
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Follow Up By: hl - Friday, Jul 15, 2005 at 17:01

Friday, Jul 15, 2005 at 17:01
Ok,

At the risk of getting my toes crushed.
Firstly, whatever the alternator puts out is fixed, it will vary a bit, but there is nothing you can do about it. Connect a reasonably flat battery to a voltage source of 14V, it will take heaps of current, in fact it will make the output from the alternator drop a bit, say down to 13V and there will be about 40 amps going into the battery. After a short while (1/2 hour of driving) the current will drop back to say 20 amps and slowly, over a period of a couple of hours, it will drop down to 2-4 amps. It may take another couple of hours after that, before it drops to less than 1 amp and that is when the battery approaches full charge. At that point, the regulator voltage will be in the range 14 - 14.4V.
Now, the long lead going back to the trailer, and I will assume that it uses decent size wire and connectors, will limit the CURRENT, it will not limit the charge voltage at all. So, while it won't take 40 amps initially, it will take longer to charge, but when the battery does get nearly full, the resistance of the wire, which should much less than 1 Ohm, will not have any effect on whether you can full charge or not. It will take longer for sure, but in a day's driving, it should still fully charge to whatever it is capable of achieving with a given alternator voltage. With a sealed battery, it is also safer to err on the side of undercharge, as you cannot replace electrolyte if it boils off. Fortunately, most sealed batteries require a higher voltage to fully charge than the alternator puts out, so that will not be a problem.
As for sulphating, that is really only a problem if a battery is left discharged for a long period. If it is regularly charged and brought up to say 90% as it will be in a car, the heat in the engine bay will kill it long before it has a chance to sulphate.
I use Exide Extreme ZZ size and tend to get more than 4 years out of them. At 140 bucks... there is no advantage to pay for fancy batteries, except for the trailer where a fully sealed job maybe safer.
Cheers

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Follow Up By: Member - Jeff M (WA) - Friday, Jul 15, 2005 at 17:26

Friday, Jul 15, 2005 at 17:26
Voltage drop over the length of cable to go from the front of the 4by to the trailer would be substantial even with very little load if the cable is not of a decent guage. If it's a standard trailer harness then the voltage drop could effect the ability of the AGM to be fully charged by the vehilce IMHO.

But hey it's all theory, personally if it were me I'd be happy doing it, but I would charge all batteries before and after trips (as I do now).
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Follow Up By: Member - Stephen (WA) - Sunday, Jul 17, 2005 at 20:26

Sunday, Jul 17, 2005 at 20:26
Brian, Jeff and HL,

Thanks again for your thoughts.

The campertrailer dudes that sold me the c/t, arranged for an autosparky to be there soa as to connect the c/t batteries to my aux batteries via a spare pin on the 7-pin plug (big one).

I'm not sure of the cable he actually used as its in split conduit all the way and I can't (without too much effort) uncover enough to find any markings on the cable. However, it's the biggest cable I have ever seen on a vehicle (barring starter cable of course). It's just about all copper and naff all insulation (comparatively speaking). He fitted about 3 inches of smaller cable right (which was still pretty big) right where it connects to the aux battery terminal. He said it was there so that it would blow should the other cable short out anywhere.

I haven't gone through the exercise to see what volts I'm getting at the c/t batteries when it's all connected up to the vehicle. Interesting point though, I hadn't considered it before really - thank you. If the c/t batteries are flattish, a fair bit of current will flow towards them and there'll be a reasonable amount of volt drop along the cable. However, after driving for a period, the c/t batteries will charge up a bit and the current demand should fall and the volt drop decrease. It'll be an interesting exercise to see how many volts are dropped over the length of the cable when I first connect and how fast the c/t batteries recover. Thanks for that idea.

Once again - many thanks
Stephen J.
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Reply By: Photoman - Friday, Jul 15, 2005 at 19:10

Friday, Jul 15, 2005 at 19:10
I'm looking at buying some AGM batts, 80Ah for $220 is this a good price?
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Follow Up By: Member - Norm C (QLD) - Friday, Jul 15, 2005 at 20:48

Friday, Jul 15, 2005 at 20:48
Probably about right. I paid $300 for 120AH. Great battery, the AGM. Charges easily. Holds its charge well (doesn't need to be on trickle), and can be used on it's side. I use one this way in the canoe for the elec motor.
Overall a great battery and worth the extra cost IMO.
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Reply By: AT4WD ADVENTURES - Friday, Jul 15, 2005 at 21:47

Friday, Jul 15, 2005 at 21:47
Hey Stephen,

My view is to take some decent cables from the vehicle batteries (in my case 50sq/mm cable) in the front of the car to the rear of the rig....do the same with the trailer from the towball to the trailer battery area and using some high quality anderson plugs to create your connection.

Now grab yourself a good 12volt dc to 204volt ac inverter and connect this to the 12volt feed in the trailer that you have just installed. Go and get your hands on a quality 240volt AC charger like the CTEK XS7000 7 Stage Charger and connect this to the 12v DC/240v AC invertor and there you have charging at the right spot, the right current, the right volts and best of all its correct right through the whole charge cycle. No guessing when bulk charge is over and switching to trickle etc or moving to float as it all happens automatically.

Now there are many variations of this setup and the one I decsribe is the most basic setup without additional relays for isolation or other sources of connection etc. but I am sure you get the picture and you can build on the design from there.

Stuart.
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Follow Up By: hl - Saturday, Jul 16, 2005 at 06:37

Saturday, Jul 16, 2005 at 06:37
Hi,

That is a good way except, in the case of a 100Ah battery and say a 7 amp charger, it will take a very long time to charge from flat, something like 20 hours.
Actually, a few new camper trailers are set up that way now.
Cheers

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Follow Up By: Member - Rob B (QLD) - Saturday, Jul 16, 2005 at 07:21

Saturday, Jul 16, 2005 at 07:21
Hi,

Do the CTEK chargers need pure sine wave? I would like to know how to select a suitable inverter.

Cheers,
Rob
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Follow Up By: AT4WD ADVENTURES - Saturday, Jul 16, 2005 at 13:59

Saturday, Jul 16, 2005 at 13:59
HL,

a 100 ah battery will take about 10-15 hrs to recharge from dead flat to about 80% but I would suggest that draining a battery to dead flat is not good and therefore you would need only need 4-8hrs to recharge a partially drained battery.

Anyway another benifit of this system is when 240v AC is available there is not mucking around to charge from this source and configured correctly the system would change over automatically when 12 volt DC is off and 240 volt AC is on.

As for running the CTEK Charger from a Modified Sine Wave invertor....I would suggest against it but thats me as I like the Pure Sine Wave invertor's for all the clean power they provide. I haven't tried the MSW Invertors with the CTEK but would think they would cope okay.....?

Regards,

Stuart M.

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Follow Up By: Member - Stephen (WA) - Sunday, Jul 17, 2005 at 20:34

Sunday, Jul 17, 2005 at 20:34
Thanks Stuart,

I have a good quality 3 stage 15A charger that I use as often as possible. I'm also able to connect it pretty much directly to the c/t batteries if I want to. The c/t batteries amount to 70 a/h at this stage (I can fit more if I want to).

I hadn't thought of running it via an inverter before. It may not be as efficient (total energy wise) but it would take the guess work out of things and the batteries would be charged as they "like it" rather than just hooked up with everything else.

Thanks for the idea.

Kind regards
Stephen J.
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Follow Up By: AT4WD ADVENTURES - Sunday, Jul 17, 2005 at 21:36

Sunday, Jul 17, 2005 at 21:36
Stephen,

GLad I could help....just make sure that the inverter is of a suitable rating to supply the 3 stage charger and all will be sweet.

Stuart
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Reply By: Member - Brian R (VIC) - Friday, Jul 15, 2005 at 21:52

Friday, Jul 15, 2005 at 21:52
It's confusing looking at charging the 3 types. Lead acid needs 13.8-14.4, virtually the same for AGM, gel cells need 13.8-14.1 max and calcium needs 14.8V.

You can easily overcharge a gel cell on a alterator, will nearly always undercharge a calcium if your regulator is correctly set for lead acid. It's all too hard.
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Reply By: Mainey (WA) - Saturday, Jul 16, 2005 at 11:19

Saturday, Jul 16, 2005 at 11:19
Stephen,
you specify; you would like to know, so that you can "re-engineer" your setup WITHOUT spending unnecessary $$$$'s.....
What you consider as “unnecessary” may be different to myself, and does not mean I’m right; I can only speak from my own experience.

IMO the way to go as far as quality of charge is concerned on a fulltime basis, ie.; long term camping, not the weekend warrior overnight stopover situation, would have to be a small/average solar system attached direct to the AGM's in the camper and when the camper is connected to the vehicle the aux battery there would also benefit from the charge. The wiring from the Aux in the vehicle should be at least the same size as the starter cable, 2 B&S would be better, but expensive, maybe cost you an extra $30, (1 slab)
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Follow Up By: Member - Stephen (WA) - Sunday, Jul 17, 2005 at 20:45

Sunday, Jul 17, 2005 at 20:45
Mainey,

Good point. We have the fridge in the back of the cruiser and we only run lights off the c/t (at this stage). The size of a solar set up (panel plus regulator) to replace the power lost from lights would be fairly small (in solar $ terms). Plus I could leave it hooked up to the c/t when it is in storage to keep the batteries constantly topped up - which is a good thing.

We tend to seperate the c/t and the vehicle when we set up camp, so I doubt that the aux will benefit much from the solar (although it gets looked after well from the alternator).

Thanks for the idea.

Kind regards
Stephen J.
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