Dual Batteries for dummies

[martynvella]

Nah, the battery is the thing that determines how much current at a given voltage up to the max the charger can supply, the only way a charger can force feed amps into a battery is to up the voltage.

The internal resistance of the battery goes up as the battery gains a higher state of charge so the current drops away.

[Qwerty]

Seems bizaare then that the battery maker just turned around and said "please set it at 14.9 wet lead acid mode. AGM setting is configured for a different plate design" (via their facebook representative) ... other than the voltage (which is too high per spec) , what difference could the AGM charge profile make?

Yet on a phone call to a different guy from the same company, they said use AGM mode as its capped to 14.4v ... the sticker on the battery says "max charge 14.4v"

Redarc say use AGM mode too, to obey the voltage.

If the voltage is the ONLY thing the "charge mode" dictates (ie doesnt affect timers / boost lengths / amperage) then i think i'll go with AGM mode... especially with super hot engine bay in mind.

[martynvella]

Just keep a close eye on the electrolyte levels, have seen many neglected MF batteries explode because the name leads the owners to believe they are fit and forget, well didn't actually see them explode but saw the mess they made, and trust me, its something I never want to see under my bonnet.

[Qwerty]

Yeah , this new one is said to be "maint free" yet it has got cell covers you can open... .ill be checking levels.

I also have a game plan... whenever i am doing a fair amount of driving / 4wding on a super hot day... I will disconnect my solar.

My thinking is : On a 40c day (60c - 70c in engine bay at battery) , i notice the redarc will completely back off... and voltage level (even if needing bulk) down around 12.6 - 12.8 ... basically the redarc is smart enough to know "this is way too effing hot , i am just going to back off"

My thought is that my MPPT charge controller which sits in the canopy (20-30c cooler in there) and doesn't know about extreme heat in the engine bay... so it continues to dump its 6amps in (because the redarc has either dropped the voltage to mid-high 12's ... or the battery is resting) .. .and i reckon that can contribute a lot of stress to the battery?

or is that a furphy? Given you say the battery will only take what it 'wants' ... in which case disconnecting the solar will have no relevance (providing it doesnt bring the voltage up to 14v which it doesn't seem to do ...)

It's hard to know whats going on, because all the time im driving in these super hot conditions, i also have fridge pulling 6 amps... a stereo, 2 amplifiers etc all pulling their needs.

So it's hard to know what "decisions" these chargers will be making.

It's either that or i never had a true over-charge scenario... and i just copped a bad battery.

[martynvella]

The redarc is cutting back to protect itself, not the battery. In theory the battery will work better when hot, just doesn't do it much good physically.

Most people disconnect the solar when using a smart charger, which the redarc is, so its output doesn't trick the charger into thinking the battery is in a higher state than it really is. If your battery voltage is getting down to less than 13 under load then it isn't taking much of a charge but it is covering the load if it remains above 12, possibly the redarc has shut down all together and it is only the solar powering the system.

In your case id be giving the relocation of the redarc to inside the cab some thought, the voltage drop of the cables will be far outweighed by the fact that it keeps charging. I have mine under the rear seat.

Also, hook up your load to a change over relay so the load is supplied directly from the main battery circuit while the ignition is on, that will save about 30% of the capacity of a BCDC1220 which would be better off going to your battery in the earlier stages of charging, and also let the charger run cooler.

[Qwerty]

yeah i hear you ... except there's no way im relocating the redarc. too hard basket, even if its imperfect now.

Yeah not sure what goes on when the charging under super heat... but redarc do say their units will dial back on the charging (and cover load) when its super hot (temperature compensation).

The redarc isnt turning off... just dials back. Actually, once or twice it does turn off entirely, and that's fine ... when its nearly 70c under the bonnet i suspect not much is going to happen with charging.

I was looking at using a relay as you suggest for load diversion, but i decided against it ... for a different issue in my system ... which is the alternator is only 80 amp at peak ... so realistically much less, especially at idle, at night ... on beaches, idling etc.

For that reason, whenever i do suffer a shortfall from my alternator ... my redarc switches off and removes the entire auxillary circuit from the equation, meaning i get prioritisation toward my essential stuff (and never suffer shortfall in my starter).

Let me put it this way , i have never ever suffered cold beer or lack of power ... so really there's no issues... just a bit concerned about whether i might've cooked a battery prematurely. And i like to micromanage shit (even if i dont fully understand it ha ha)

Then again SuperCharge said my allrounder was cactus due to an internal short / busted cells and didn't think over charging was to blame ... other cells were healthy. It was 2 months out of warranty, typical!

[martynvella]

That's the sort of thing that you would expect a battery to die of in severe conditions. Something your just going to have to live with.

[Qwerty]

yup .. it's not kind! We go beach combing (low speed, , soft loaded work) on 40c+ days ... often stationary but with engines and aircons running (usually with kids / wives hiding in the aircon while we navigate a soft bit of beach) ... im surprised the cars handle it sometimes!

Sand so hot you can't walk on it.

If anything, relocation of the aux battery entirely out of engine bay is desirable, but i truly can't be assed.

next build i will do things a lot differently.

I didnt want it in my canopy because it'd take up sleeping / loading space.

that and i had underestimated how hot the 1GRFE engine bay actually gets, especially at the rear of it.

the starter battery area next to radiator is about 20c cooler.

Non issue in the D4D engine bays, they are wayyyyy cooler.

[Qwerty]

ps thanks for chatting

[miccos]

Quick question on 2nd battery locations. I am guessing there isn't enough room behind the rear seats?

Thought it would be a good spot if the space was there.

[Qwerty]

Not for 105ah that I can tell. Plus I have two baby seats installed which are a pain in ass no way am I pulling them in and out just to access battery etc

If I were to start again I'd go false
Floor in my tray but not going to re invest on this particular build.

Next 4wd ...

[miccos]

Ahh thanks Qwerty, was more for me as I have a blank canvas.

Expecting my first child in March so if the baby seats are going to make life difficult(and not enough space anyway) I can just stick with the tried and tested under bonnet.

[Qwerty]

Could go a couple of half size AGM's behind the seats i guess? ... with a dcdc charger. Certainly keep them cool!

As i say, if i had my time again i'd probably put a false floor in my tub ... or do away with tub altogether and get an Ag Tray with canopy etc... but thats a lot wider topic than just batteries.

And yeah , once those baby seats are in, they stay! ... least with ours, it was a bit of a pain, not going through that if i dont have to!

[07luxyTD]

Look for a brand called "kickass" batteries. They sound cheap but seam to preform quite well. They do tall slim agms which would be suitable for behind the rear seat.
Eg 120ah
http://www.australiandirect.com.au/buy/ ... A12120Slim

[xychix]

Set your redarc to its lowest setting for heat reasons, it wont be hot when it is on your ac charger.

yeah both the charger and battery makers got back to me today and said put on the 'softer' AGM setting which max charges at 14.4

More so due to the extreme heat my engine bay gets.

either way AGM is gunna be the mode ... other two are too high a voltage.

Althogh confusingly, the battery maker just said "please set it at 14.7 wet lead acid mode. AGM setting is configured for a different plate design"

confusing!

Encouraging to see we all draw a similar conclusion.
Commercial parties tend to advice lower charging voltage as it is the 'safe' advice. The battery might last a little shorter but is less likely to explode No law suits

It is important though to check if the battery has a vent / connector for a hose where it can dump it's pressure / gas

However , i was charging at the time with my AC-DC charger (set to calcium mode up to 16v) ... which started at 8pm the night before. I came out at 8am and it was still in bulk mode! ... hissing and boiling.

I am not sure, but i have a suscipicion the AC charger might occasionally lose its marbles and "stick" in boost mode.

Well if the battery can't make the 16V It might stick at 15.x boiling the hell out of itself while the charger is stuck in bulk mode convinced it should reach 16V at a certain point.... 16V is just to high. Wouldn't say the battery died though (atleast not if you can refill it). Likely the plates are a bit thinner now but they will be boiled nice and clean. Top it up with 'pure water' (how do you call that in English??) and measure the voltage. I'd give it a long charge with a 'slow' charger. If the battery prints 80A C10 I'd try and have it on a 4Amps charge at ~15ish Volts for atleast 80/4= 20 hours in a nice cool spot. You'd be supprised what you can do with a battery. Then let it settle for a night or two. If it then reads 12.5+ you should be fine. It might lack a little capacity but you should be good to go. You can apperantly 'weigh' the amount of acid in the fluids as well and add acid.... although I'd not do that at home and/or without safety gloves/goggles

Nah, the battery is the thing that determines how much current at a given voltage up to the max the charger can supply, the only way a charger can force feed amps into a battery is to up the voltage.

The internal resistance of the battery goes up as the battery gains a higher state of charge so the current drops away.

That might explain the problem with the charger. We don't know it's exact program but if it was set to reach a certain voltages (16+ V) as the type of battery is assumed to accept charge up to that point It might have been boiling for a while.


One other point that hasn't been mentioned. Keeping the batteries 'at level' sounds good. However it doesn't harm them, will even be good for the batteries (lead-acid, thick plate) to do a decent 40 ~ 50% discharge from time to time.

so a 80A C10 will benefit from an occasionally 4~8A for 12 to 8 ish hours. (preferably monitor voltage doing this and cut out below 11.8 or so (atleast that's how I've set mine up)

[martynvella]

Smart chargers have a minimum and maximum battery size recommendation, if the battery is too big it wont be able to achieve the programmed voltage and continue in bulk causing excessive gassing.

[Qwerty]

hey Xy : the battery that died was sealed ... and the battery maker diagnosed it as completely stuffed... busted cell / shorted cells (something like that)

All good ive got the new wet lead acid antimony installed, have set the DC DC to AGM ... time will tell.

I will just start being a bit less happy to throw the ACDC charger on it so often and if i do, i'll keep an eye on it.

One auto sparky reckoned the projecta's are prone to "cooking" batteries for some reason ... and i suspect it may well be due to me having load on at the time so the projecta just went nuts with charging bulk.

In speaking with redarc, their DCDC's are a bit smarter , not entirely sure how exactly, but they're designed to detect and accomodate load. Whereas my projecta should be set to "PWR SUPPLY" mode if you have load (it is written in the manual but whoever reads them!)

I've since ruled the solar out, the solar goes to float as soon as any other charger is involved ... and it doesnt alter the system voltage.

[xychix]

hey Xy : the battery that died was sealed ... and the battery maker diagnosed it as completely stuffed... busted cell / shorted cells (something like that)

sealed batteries are not to be cooked back alive as the might explode. To bad, it's likely dead then

I will just start being a bit less happy to throw the ACDC charger on it so often and if i do, i'll keep an eye on it.

One auto sparky reckoned the projecta's are prone to "cooking" batteries for some reason ... and i suspect it may well be due to me having load on at the time so the projecta just went nuts with charging bulk.

yeah I'd only have an AC-DC charger with a slightly high voltage on if there's no load. Consider doing this once every 3 of 6 months. drain/use the battery to ~11.8V (max 40% of total Ah withdraw) and then a charge on 14.9ish without extra load.

Can't find it now but you had a 110Ah right? so charging ~50Ah as C20 (5.5Ah) should be ~10 hours of bulk loading. Meaning you should be safe charging AC-DC in a garage starting late at night (if 5.5 Ah max) and check it the next morning and from then on keep an eye on it.

[Qwerty]

yeah it was hissing (so i guess not entirely sealed???) and i could hear her boiling.

Funnily enough when i took to the battery manufacturer they were all positive and asking me to leave it with them as they reckned it wasnt dead (despite reading 10.8v after 12hrs on bulk) ... next morning "no mate its completely toast" LOL.

Yeah I'm guilty of the load thing... but basically i would do that in super hot days, my fridge is always running in the hilux , so ill just use PWR SUPPLY mode in future when attempting to inject some run-time into the system.

Generally during the day it almost holds the fridge needs ... but on those 40-45c days where my fridge is working super hard (and it barely gets below 30c until midnight) so i start to outstrip the supply. A good drive sorts that, but often i only drive 10 minutes in a day, and sometimes she's parked up for several days with no engine run at all, so its all down to solar.

So... i was just throwing my AC_DC charger onto it, and walking away ... but i suspect doing that (probably 6 times in 6 months) during heat-waves has killed it (especially when it was set to calcium 16v mode) because the near constant fridge loading and bloody hot nights was causing overcharging scenarios.

if i have to go to hassle of disconnecting load (and liekly running AC power to the fridge) then i'm just as likely to power the fridge off until the next trip. Must say i do like having a cold fridge onboard 24/7 ... usually have a few ciders, beers, and waters in it

Bottom line the stress these systems go under in super heat is pretty high.

[martynvella]

What is the output of the charger qwerty? If you run it in power supply mode that don't usually get much higher than 13.8 volts which is a little higher than float on most non selectable smart chargers but it should be able to run the fridge ok without over gassing the battery.

You might be starting to over think things, the battery that failed might have had nothing to do with your charger, if it had a shorted cell it would have appeared to be boiling on a 14 volt charge. Heat and vibration is the most likely cause.

Running a fridge on a hot day shouldn't be a problem for the system, yes they work harder but if it cant cope then there is a design problem somewhere.

I never charge my aux with an ac charger, the redarc does it just fine, but I do plug the fridge into 240 when it is at home running for more than 12 hours. I do make sure the lead goes via the drivers side so I don't forget it is there and hop in and drive off.