Engine battery parallel 12 volt system?

[WalkaboutTed]

I'm slowly working on my electrical system, though getting rid of crap and readying the house for sale is the priority.

Got a question. The stock van I have came with an 80ah battery, which I imagine is a marine battery. It also has two 12 volt outlets, 1 USB outlets and two AC outlets, one 400watts and the other 120watts.  The built-in inverter is 400 watts. Even though we've camped a lot, we still use a fair amount of power and I can see our use, once we are full time, increase exponentially.  While camping, husband lugs the group 27 Costco marine battery to the tent and we use it for tablets, phones, inflating the queen size air mattress everyday (it leaks), ebooks and charging all of our USB items.  We manage about 10 days before I run it down to 12 volts (we beat up that battery-2 years of poor treatment so far and it keeps coming back!), And then we bring it to where we can use an AC plugin charger so we can abuse it all over again.

We'll have the 300 ah of cheapo UPG AGMs, but will be using them hard to run our 800 watts AC Keurig type coffee machine.  Obviously, no more coffee if we hit about 12.2 until we charge the batteries via solar, alternator or going where we can plug in to do a full charge.  

It would be nice to be able to use the engine battery as a back-up.  Not for coffee, of course, nor do we need to blow up an air mattress any more.

My question is, can I run the starter battery the same? The CTEK unit also charges the engine battery with the solar, but I wouldn't count on it too much if there's not a lot of sun.  How much can I abuse that battery without needing to call for a tow/service? Or, how hard can I push it?

I wouldn't treat my husband, kids or dogs that way, but a little bit battery abuse is not beyond me.

 

[John61CT]

11.9 or 12V is the point I would stop using the Starter, and many isolators, combiners, ACRs and battery-to-battery chargers will automate such protection.

Or monitoring systems that will sound an alarm.

Carry and keep charged a little jump start pack for belt & suspenders.

 

[Trebor English]

With the group 27, the AGMs, and the van starter battery I would avoid hooking them all in parallel unless you have a charge source going.  Between the 27 and the AGMs I would be inclined to leave the starter battery out of the usage mix.  Deep cycle batteries are good for 50% max use.  Starter batteries don't like being cycled much at all, avoid more than 10%.

 

[SternWake]

There are all sorts of strategies you can use.

The engine battery does have usable capacity you can tap into, but as said a regular flooded starting battery will not like being put in parallel with 3 depleted AGMS, but that gives you an excuse to put a bigger better battery up there that can tolerate some cycling better when it inevitably fails. can you squeeze another UPG group 27 AGM wherre your current engine battery resides? it easily has enough CCA to work as a starting battery.

Have you used the coffee maker on the inverter and batteries yet?

Will you utilize an ammeter and voltmeter to measure the load while it runs?
You might find that you do not require tapping into more 'emergency coffee capacity'

When I had 2 house batteries and one engine battery, my strategy morphed into keeping the engine battery as full as possible at all times. And it wound up lasting 7 years.

Bout 13 years ago, I was deep in Baja had been parked for weeks without moving or starting engine, and drained my house batteries to the point my Inverter alarm was screaming.
All I had to do was turn a switch to parallel my engine battery to my house bank and stop the screaming, so I could indulgently keep listening to music via my laptop's library as I slowly packed up camp.

Sooner than expected, the inverter alarm started chirping, but I was nearly done packing up camp anyway. So I shut it down and started the engine on all 3 batteries. They Easily started engine. It Was not even a slow cranking. But after starting, my stock dashboard ammeter rose up higher than I ever saw it go before with 3 very depleted batteries and a voltage regulator seeking 14.9v.

I lowered my electric windows while watching the abnormally high ammeter, and the ammeter fell flat. The charging system quit working. The voltage regulator was sending 8 amps or possibly more to the alternator field terminals, and something on that circuit was overwhelmed.

I was able to drive for a bit on those 3 dead batteries, more like 2 dead and one weak one. I traced the whole VR circuit, replaced wires, stressed out and failing to see charging voltages after the engine start. I must have restarted it 20 times on those 3 depleted batteries, trying to see if my ministrations were effective. They were not.

My point, is that lots of capacity of very depleted batterys, in parallel, still has a lot of cold cranking amps and will likely be able to easily start the engine.

Mine, when that occured, were all different age and size batteries too, and also had inadequate cabling between them. Very far from ideal, yet proved more than adequate for engine starting. I also had a small well used jumper pack, but it was dead from helping other campers.

That Baja venture ended after I got into town, recharged all 3 batteries from their grid, and was going to make a run for the border. I got 10 miles and the ammeter gauge jumped back to normal and my voltmeter showed 14.7v.

What I 'think' happened back then, was the brushes in the recently installed remanufactured alternator were not broken in to the commutator and when the voltage regulator sent out maximum field current to the brushes, the brushes glazed over and opened the circuit.
After all the batteries were fully charged there was not much field current sent out and the glazing eventually wore away as I drove.

That was back in 2004 or so when most of this was still a mystery to me. I'd be better able to diagnose it now. It 'could' have been the alternator field wires at the ECM, but if so they did not present issues for another decade.

If you'd feel better about a healthy more capable engine startong battery, then An AGM from Northstar or Odyssey have very high CCA figures, and can more reliably crank an engine when very depleted.

These Thin plate pure lead AGM batteries need some loving after a deeper cycle, intentional or not. Generally high amps and they really really love to be returned to full charge as often as possible. They get more petulant than a flooded battery would if only retruned to 95% time after time, and one would likely not get their moneys worth from them.

Northstar AGM's are relabelled and sold as X2Power at Batteries+ with a nationwide 4 year warranty.

https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=batteries+plus+x2+power

My 90Ah group 27 northstar AGM battery the other morning started my engine when depleted 57AH of the total 90. It is nearly 38 months old and has 450 deep cycles on it and is just now beginning to show its age where I am considering getting a small emergency lead acid jumper starter battery I can easily install, and remove.

If I was feeling rich I'd want the Odyssey pc625

https://www.amazon.com/Odyssey-PC62...ie=UTF8&qid=1485229458&sr=8-1&keywords=pc+625

But this UB12120 was the battery in my jumper pack:
https://www.amazon.com/UNIVERSAL-PO...e=UTF8&qid=1485229963&sr=8-6&keywords=Ub12120

 

[WalkaboutTed]

I should clarify what I said about using the engine battery as a parallel. I am keeping my engine battery separate from the house batteries (or, if as they call them in the UK, "leisure batteries"). I want to be able to use the starting battery as a fall back system in case I've drained my house battery bank to where I don't want to damage them further with too low a SOC. If I can do that for a day or two to get us over the hump, good. I would stop using the house batteries if we were too close to depletion. In any case, I have the fridge circuit on the "non-critical" output on the CTEK and it will cut off at a certain (in the elevens, I think) low voltage, so if that's the only thing running, we should be fine. But Hubby wants his TV and I my laptop and other goodies, so if we can get through a "low energy" evening or two, that would be good.

That's reassuring about the engine battery being able to turn over even if I were to run it down a fair amount. Batteries here in the Arizona desert are not known for their long lives-though our Subaru went 7 years before replacing and the Element, 4 years when we replaced that one prophylactically. We would probably replace this battery much sooner, given the fact that I don't want to be stuck out in the middle of nowhere needing a new one. That's a good idea about replacing the battery under the hood with a psuedo deep cycle (UPG) one.

No, we haven't run the coffee maker on the inverter yet. I just got the cables and haven't gotten around to it yet. If we can't run the Keurig, I imagine we would be able to run one of those four-cup coffee makers, provided we don't use the warming plate too long. But I love the consistently perfect k-cups, and coffee is the only thing that can get me out of bed in the morning. I put out my hand, croaking "coffee!" And can't open my eyes until the second cup. Thankfully, Hub is a morning person and is able to accommodate.

I just want to be able to start the engine if we run out of juice on the house bank, while not being power deprived in the meantime . The charger system will let the alternator pump in as much as 100 amps (though my alternator is only 130 amps), so starting juice is all we need. I would prefer not running the engine just to give the battery bank a nudge. Especially if we have neighbors that we don't want to disturb with noise or exhaust at an inopportune time.

It's not that I'm systematically going out to kill my batteries, I just want what I want, when I want it. Besides, from what I've read here, every newbie needs to destroy the first set of batteries in order to learn how not to murder the next set. I DETEST getting stuck! Hub's 10 year old Subaru died while we were out, twice in a month, needing towing and I refused to ever step foot in it again. Waiting for a tow in 110F heat (isn't that pretty much when all breakdowns occur?) is not my cup of tea. The other tow required a 17 mile trip down from 7000 feet altitude. Aint gonna happen again if I can help it.

I have a voltmeter on the battery bank and separately, on the starting battery. I have one of those clamp multimeters to use as an ammeter until I decide what monitoring system I'll use. Looking at the Bayite monitor, that shunt thing looks like a pain (translation: uh, I don't understand it).

You guys are such a super resource! Thank you!

 

[WalkaboutTed]

Oh, the starter battery is an AGM, if that means anything.

 

[John61CT]

Is your CTEK the D250S DC-DC ? If so, you should look at the SmartPass add-on, ​bypasses the D250S with a direct relay connection to the Alt, which boosts your charge rate during the bulk phase when the target battery is low, and wants to charge faster than what the D250S can supply.

But if you make *long* trips regularly, or get most of your needs met from solar, then it may not be worth the extra expense.

 

[WalkaboutTed]

Yeah, I have the Smartpass. I'm hoping it will be smart enough for me to ignore the battery system as much as possible. I know how important for AGMs to get as complete a charge as possible. Thankfully, between husband's and my retirement income (not great because we retired early, but enough), we will be able to stay at a place here and there where we can plug in and recharge our batteries if the amp hours start slipping away.

I'm a fan of making things idiot proof (of course, I'm never the idiot), so I also got the CTEK 25000 AC/DC charger. The costs of these things hurt, but once in, I think it'll work well enough.

Thank you,
Ted

 

[SternWake]

With the 3 group 27 house batteries, and the engine battery in parallel to spin starter motor you should really be able to start the engine even when the all batteries are own in the 20% charged danger zone.  As long as it isn't a diesel engine in sub 20f temps.

Does the Ctek allow for self jumping?  IF not bring a big enough jumper wire or jumper cables to hook house bank to engine battery for emergency jump starting.

Or just carry a jumper pack. or just a dedicated jumper battery instead of a pack:

https://www.amazon.com/EnerSys-Gene...coding=UTF8&psc=1&refRID=D0B3186BPMV72D9EV45R


I might be picking up one of those as my Only battery is  finally starting to show its age and mileage

With a voltmeter on engine and house batteries AND the clamp meter you will quickly see how much you can use from your batteries and get a sense of it.

I don't think you will be one of the newbie battery murderers as long as you use these tools and get a feel for what and how much the batteries can handle.

If the batteries are down in the 12.2v range under non coffee making loads, and coffee is needed, You could start engine while powering the coffee maker.  I would not idle for hours just to recharge, but to offset the huge inverter/coffee load for a few minutes, no worries.

Going below 50% is not instant death on batteries.  But going to 20% leaving them there for 3 days then recharging them to only 50% is certainly very hard on them.  The lower the discharge however, the more important it is that  a prompt and full recharge is performed.

Much of theses systems work great, when the batteries are still pretty new.  It is when the batteries are aged and harder and slower to fully recharge that it can begin to get stressfull.   The better one can treat the batteries when they are new, well the day when they become marginal is just that much further away.

 

[John61CT]

Is the Alt hooked to the House bank? that's what I would do, set the Starter batt as secondary, only gets topped up by solar when camped after House is full.

Personally I'd make sure House was big enough so Starter only needed very rarely, but with a jumper pack you should be Ok, especially with the nonessential loads feature cutting them out at 11.5.

Just note you can't route big loads like the fridge through there, so in that scenario, do think about getting a good SoC monitor.

 

[WalkaboutTed]

I'm not understanding how to line up all four batteries in parallel for starting if need be. Or how to make the starter battery as secondary. A big reason why I bought the CTEK system is because it was an easy system to set up-fairly idiot proof. I'm a nurse and have no technical background, so this is a big learning experience. Hub is retired math teacher, so no help from that direction. I paid someone else to run the cable from the alternator to the battery bank, so I don't feel comfortable crawling (nor am I physically able to) under the vehicle to run another cable back to the starter battery, it that's what is needed.

I haven't seen the function for jumping without cables, but we'd bring them anyway. Space will be limited, so no jumper pack or battery-I'll just be vigilant. I've lived so much of my life on 12 volts and propane (and an alcohol stove long ago), but I don't want want to live with too much constaint, energy wise.

John61CT, you mentioned that I shouldn't run my fridge on the non-critical hookup. It's a 10 amp circuit. I was planning to run one an arb or dometic type chest coolers. Will that go over 10 amps? The CTEK instructions specifically show putting the fridge on that circuit.

I think my takeaway will be to replace the starter battery with a deep cycle battery. I was hoping that since Nissan puts in what they call an "80 amp hour" battery, that it would be at least a marine battery, given the built-in inverters for business use. I'll check it out tomorrow. It's cold out there tonight (45F already Tucson wussy weather).

Now I just gotta learn how to use the clamp meter to calculate how much power we are using.
Thanks again,
Ted

 

[SternWake]

12v dc Compresor fridges would max out at 6.5 amps.

If you need to tap engine battery for more juice then jumper cables would be the easiest method for doing do.

If the EZ pass system can be manually controled that would be easier, but I am not familiar with the product.

Please watch this video regarding the proper wiring up of 3 batteries in parallel and what happens when they are not.



Meaning all load and sources to one parallel battery1 (+) and all load abnd sources to battery3(-)

The jumper cables between engine battery and house batteries would be bad if left in place for longer than it takes to make you emergency coffee.

 

[John61CT]

As long as you're aware and keeping under the specs you should be right on that non-critical circuit.

The jumper pack type I meant is the size of a paperback book, in case you thought of the bigger ones.

The CTEK apparently doesn't have the "momentary self-jump" circuit I thought it did, so jumper cable will do.

But if you do ever get a pro to rewire things for you and want a convenient switch for this, here's a post with an example diagram at the end.

http://myselfbuildcamper.co.uk/the-jump-start-system/