Wanting to increase my boon docking capability.
I have 4 golf cart 6V batts for a house bank. 2 Gr 31s for starting, where the 8Ds used to be. They connect and disconnect to each other with an automatic switch, which can be overruled to the connected position. If I removed the Gr 31 starts, I would have room for 4, or even 6 golf cart deep cycle batts in the start batt compartment. That would double, or more, my house bank capacity. I am sure that the house bank would start the main engine just fine. If I sucked it down too low for starting, I could start the generator (it has it's own dedicated start battery) to recharge the bank enough to start the engine. I start the generator anyway when I see 50% SOC or less. I have solar too, but that is a subject for another post.
Thoughts, advice ?
JC
I would never use the house battery bank as a starting battery and vis-versa. Totally different types of batteries. Start batteries are designed to dump a huge current flow in a hurry, and house batteries are designed to provide steady current flow over a long period of time. There are mix-use batteries (as in marine batteries) but they are a compromise for both purposes. You're already going to be stressing out those type 31 batteries if you ever get into cold weather or have a difficult start.
What I did was to get 6v batteries with much more capacity than a 'standard' T-105. I'm running four L16g batteries from Trojan, which provides 780 Ah @12v. There are a few different batteries that provide almost as much and still fit into the footprint of the T-105, providing that you have a few inches extra height to spare.
There are various ways to skin this cat, but scrapping the start batteries wouldn't be my first choice.
There were engineers who used to dabble here that said they'd just make one big bank of deeep cycle, if they messed with bus conversions again.
Large bank won't be harmed by the start current, disabling the bus thru careless power management was punishment for being so stupid to do so. Wasting the money, space and weight for a set of start batteries that barely do anything offended the priorities of efficiency.
Do your math, how many amp hours does the starting event typically consume, what percentage of the bank capacity is that calculation?
Do it your way, know that smart peeps have considered doing it.
Happy coaching!
Buswarrior
Yes I have read that some people do away with the start batteries, and only have a large house bank. I never start my engine cold. I plug in the block heaters (2) to warm it up before starting in the morning if it is cold out, like 40F or less. I run the generator anyway in the morning for breakfast. The engine then starts easily and the starter doesn't draw much. Same later in the day: I just show it the key and it starts, lol.
So I wonder what harm it would really do to a deep cycle bank?
JC
Is your engine start 12 or 24v? 24v would require a series parallel switch.
I have though about the same thing .
I have 4 x 12 volt start batteries right above the 6 x 6 volt house batteries on a slide .
that would make 10 x 6 volt batteries ! at 225 amps per set or
1125 amps . this is on a 12 volt start and house system
now saying this it does take a lot to start the cat but with 1125 amps there should be lots of power ?
J C go for it and let me know how it works
thanks dave
Are Ah of total capacity in a deep cycle the same as CCA in a start battery?
AH and CCA are different measures.
The oomph of thin plates in a start battery will more than be made available by a large bank of thick plate deep cycles.
Way too much false religion gets passed around about batteries.
We are not typical battery users, many horror stories are based on minimalism abuses, battery capacity too small for the job at hand.
If power use and replenishment hangs in the balance, the batteries are being worked hard, and will bite back.
Large battery bank has lots of advantages as far as re-charge rates, if you can muster the amperage. Some with big solar, need a bigger bank, or they have too high a re-charge rate.
Shed the false prophets, you can unlock a bunch of battery money, and make that lead useful to you.
Happy coaching!
Buswarrior
I will go for it. And let you all know how it works.
JC
Also to make the point that "deep cycle" is a much abused term which really has no defined meaning. Manufacturers can, and do, stick deep cycle labels on anything they want to sell as a 'leisure' battery, even if in fact it's not constructed very differently from a start battery, complete with a start battery's short lifespan. On the other hand a "proper" deep-cycle battery - for instance an industrial traction battery designed for a thousands of charge cycles - will weigh very considerably more, have a much lower output rating, and will last almost indefinitely.
As with all discussions of this sort there is really no satisfactory answer other than to understand how to properly interpret the specs of the batteries you're comparing, and then sit down and do the math. Personally my instinct is that, if you're talking about proper deep cycle batteries, you're going to need a lot more of them than you think to be able to replicate the short-term output capability of a purpose-designed start battery
Jeremy
my starts have been my house for 15 years...DEKA Marine AGM.
I have had as many as 4. but generally only 2 8D.
Gen has isolated battery, toad has jumper cables.
And no i don't boondock for weeks, just off pole for a few days (but a few times a week) and have no qualms about running my gen off quiet hours.
never lost my ice cream never got stranded.
I've considered similar.
Like others have said, when your parallel 6 or 8 deep cycle batteries, they outperform the best start batteries.
Go for it. Just make sure you have some fall back option for starting a generator.
The difference between start and deep cycle batteries for starting purposes comes when the battery is minimally sized for the application. OEM's like to size a battery to the application, no more and no less, and that is good engineering. Two Gp 31's starting a cold 8v-71 is an example of this "enough but no extra" sizing. What that means is the start battery, with lots of thin plates, delivers the several hundred amps of starting current by ripping the charge off the surface of the plates, and then replenishes it fast by charging hot from an alternator. If you substitute a deep cycle battery of the same size and capacity of the start battery, it's fewer thick plates won't deliver the starting current and won't accept the fast and sudden charge after the engine has started. Hence, the "don't use deep cycle batteries for starting" mantra. For us, the deal changes dramatically. We take a vastly oversized, huge deep cycle house bank (huge in comparison to correctly engineered start banks) and draw a quite small percentage of capacity to start the engine. Then, the inrush of current to recharge after starting is a lot less, and is easily accepted by the large bank of batteries. More than one manufacturer (but Deka is an example) recommends deep cycle batteries for exactly this purpose. The only reason I wouldn't do it is redundancy. Having two dedicated, separable banks means you can lose one (as I did on a trip once), separate it out with switches and run everything off the other bank until you can replace batteries. I had a start battery fail on a trip.
I like redundancy, especially when it comes to starting the main engine. Electricity is leaky stuff and has an affinity for smoke so any little bit of smoke allowed in or around the coach and the next thing you know your electricity has all leaked out to follow it. When that happens it sure is a good idea to have two battery systems with the ability to bridge them together. Separate battery on the genset? Great idea. But Murphy hides around those things too. Solar? Fantastic, but... And battery chargers have been known to fail. The excuse of not duplicating is a fallacy. If you need more house batteries it means you are discharging them to where they would have trouble starting the engine. Do that with a combined system and, well you will have trouble starting the engine.
In the end it's all about being able to start the main engine. As you begin to whittle away at the options you have for doing that the odds of not being able to increase proportionally, so what it comes down to is, are you a gambling man? After all, it isn't like you can jump start it off a Yugo.
Jim
Thanks Brian, good explanation as usual...
How often would one bank fail, so you needed redundancy? Not often. The bigger risk would be to overdraw the bank and not be able to start the engine. But as I stated above, I am careful not to suck down below 50% SOC. And if that happened, the generator has it's own dedicated battery.
JC
It will work JC later change out the starter to the MT 39 Delco that doesn't require the 900 amps like the older Delco 42 starters do and you will be ok ,the 39 Delco is a amazing starter it reaches the magic number of 60 rpms on half the power
Our main engine start batteries are a pair or NAPA commercial
8D deep cycle batteries that are labeled "also good for engine starting". Our house batteries are 3 group 31 deep cycle batteries. We can switch the house power draw to the engine start batteries & do so while driving as the alternator keeps them topped off. Our Onan generator has it's own dedicated start battery & when running is separately charging both house & engine batteries as two separate systems. The setup was originally our design due to a neg. ground house system on a positive ground chassis system. When we recently converted to negative ground chassis we maintained the original battery set up because it has worked well for us through the years. As of yet we don't have large inverter or solar power and rely mainly on 12 VDC & LP gas for house systems. It works well for us.
This reminds me of the old saying,: If it ain't broke don't fix it.>>>Dan
One other thing to remember about a single bank.. In a series parallel system no mater how large the "bank",, if you loose one battery you loose the bank.>>>Dan
And occasionally you should check and compare specific gravity of each cell to the rest. Some of these new battery analyzers may do this job quicker.
"Losing a battery"...
How would this go unnoticed?
With all the lovely monitors that have been available for many years now...
So much of the "advice" out there is to combat the foolishness of running blind. Mix in a set of crap batteries bought on the cheap...
Way too many variables.
Get the modern State of Charge equipment of your choice, PAY ATTENTION to it, do your proper, manufacturer recommended periodic battery maintenance and enjoy the reliability, and long life, of your large battery bank?
Happy coaching!
Buswarrior
the use of a bogart system or same is a must
A bad battery can happen on any set up . I use a battery hydrometer on my coach system and record the readings . Worst case you could rewire out the bad battery ( or 2 ) to keep the system at the right volts on the road if you had to . I have a towed to boost the genny if I need to and as a last resort I carry a fully charged lithium 2000 amp boost pack .
the other problem I have is my start batteries ( 4 x group 31 's ) I can't open them up for testing or adding water ?? but have a 400 amp switch over from bank to start batteries now if needed
when my start batteries crap out I think I will do the change to one bank at that time
again go for it J C
dave
Yah,, go for it JC,,you first... ;D ::)>>>D
I will.
JC
Its a very sensible solution JC. We had more or less exactly what you are proposing on the boat. I was nervous at first but came to realize that it was a very sensible solution. In the situation where you carry separate start/house batteries you are lugging around a bunch of lead in the start batteries which is only briefly used, at most once or twice a week. As others have advised I would definitely put in a good state of charge monitor. I'm a big fan of Bogart but there are others. I set my Bogarts very conservatively and then use the batteries equally conservatively. We absolutely never see 50% discharge but even if we did the batteries would still be above 50% because of the way I program the monitor. My only caution in your situation is that I wouldn't want to mix ages on my batteries in the same bank which would mean either separating the banks for charging or replacing all the batteries.
Thanks Bob. I do have a good state of charge monitor.
JC
So I installed 4 deep cycle golf cart batteries (6V) in place of the 12V start batteries. They are tied to the existing 4 batt house bank. So now I have 8 batts in series/parallel as one bank. I also added a solar panel for a total of +- 700 watts.
We have used the bus several times since, and I am very happy with the results. The increased batt capacity is quite noticeable. The solar panels recharge the bank quite quickly when the sun shines. Of course it doesn't do sh.t on cloudy days, and we have to run the generator. Starting the engine is just as easy as before. It hardly takes anything away from the batts. Granted it is summer so it is warm. But as I mentioned earlier, I always preheat the engine in the winter before starting anyway.
So that was a good improvement to the bus.
JC
Glad to hear you went for it and all is good
as my starts crap out I am going to do the same
dave
Good to hear it worked out. Thanks for coming back to us with the end of the story!
Lovely report, rounding out the thread.
Happy coaching!
Buswarrior
I worked on a few cell tower generators the starting batteries were part of the backup electrical system for the tower no separate starting batteries for the 750kw 12v92 generator surprised the hell out of me
In this situation, a set of dedicated start batteries would be the ones that couldn't be trusted and require extraordinary observation
Completely the other way around, the cell back-up is thought of as more reliable and measured...
It's all about perspective and monitoring
Happy coaching!
Buswarrior
This might nowadays be a more philosophical question than a strict MODERN engineering solution. Separating the main engine starting batteries from the auxiliary power batteries. It might be more practical to separate the two. This includes separating ALL House or Coach functions from the automotive chassis. This includes the whatever engine starting batteries from the house Bus Conversion Motor Home batteries.
If your can not start the main coach engine and drive out of whatever dire emergency situation that might occur, then you might, (might) be setting yourself up for a major failure that may have far reaching consequences. Flash floods. Fast moving wild fires. Tsunamis. Civil unrest. Separate the house from the chassis. This is common sense. You do not want non cranking main engine batteries in a critical situation.
Another good reason to have the ability to separate main engine fuel from the generator fuel tank. Another good reason to carry a spare tire, (maybe two) with the ability to repair OR CHANGE OUT the leaky tire. Another reason for a comprehensive spare parts collection. Lots of tools plus the ability to make hasty road repairs. No cell service. No roadside rescue. None whatsoever. Only you. Yikes indeed!
What do you have in place to protect this combines house/chassis battery system from inadvertently running it down too far? Sounds like it's capable of starting the bus, but what happens if it gets discharged too far? Are you just planning to use the generator and/or solar to recharge or is there something to protect things against going below a set point?
When we camp, especially when dry camping, our chassis batteries are disconnected unless they're on the charger. I want to know that I can crank the engine should an emergency arise and we need to move quickly. Not saying that your system can't do this, but I'm curious how.
It will work for you JC ,you may think about using a MT 39 starter when your 42 goes bad a friggin lawn mower battery will start one with the MT39 starter
Quote from: HB of CJ on August 27, 2019, 08:25:06 PM
Another good reason to have the ability to separate main engine fuel from the generator fuel tank. Another good reason to carry a spare tire, (maybe two) with the ability to repair OR CHANGE OUT the leaky tire. Another reason for a comprehensive spare parts collection. Lots of tools plus the ability to make hasty road repairs. No cell service. No roadside rescue. None whatsoever. Only you. Yikes indeed!
I agree. While some people rely on others to do things for them, the virtue of being self-sufficient and resourceful is very satisfying and practical. I carry tools and spares, and I try to always have one or more ways to solve a failure of some part. Isolating the batteries from each other, but having a way to connect them when there is a problem, is part of that. Even if you have a road service plan, there are times when a prepared person can get things fixed long before a service person shows up.
I feel totally prepared and self sufficient. Like I said earlier in this thread, I do not let the bank get down below 50% state of charge. It will easily start the engine at that. I have a generator with it's own dedicated battery that is charged by solar, generator, or shore power, so it is always ready to go. I remember a few years ago when my batteries were old and weak and sometimes would not crank the engine. All it would take was 5 minutes of generator time to boost the batts enough to turn the engine over to start it.
My inverter quits at a set voltage (I don't remember exactly what at the moment) to protect the batteries.
I know I have gone out on a limb with this where many of you wouldn't dare venture. It is working great, not just on a weekend trip, but on extended journeys. And I am not the first one to do it.
Don't we all drive cars with only one battery? With no solar or generator back up...
I have driven many modern passenger coaches with only one set of starting batteries, off which many auxiliary systems are fed, like a Webasto coolant heater, audio/video to rival a concert hall, AC outlet and USB ports at every seat, lighting, etc, that can all be operated with the coach shut off. As in my bus, the inverter shuts down at a set voltage to protect the batteries to be able to start the engine.
We all do it our way...
JC
True - many ways to go about this.
The comparison to passenger vehicles is a little different though, as they don't typically camp for days on end using the batteries.
On our system I added the Victron battery protection device. It's an automatic battery disconnect that you can program to whatever voltage you want, and it will disconnect at that point. Took a little fiddling to get the voltage set right on mine so that it didn't shut down from a monetary voltage drop due to a large draw, but I like knowing that if I forget to shut something off it will prevent damage to the batteries. Also had to move my charger feed to allow battery charging once the Victron shut things down.
If a busnut wants to spend money defending against imagined Boogey men, personal mistakes, or faulty run-out equipment, we are free to do so.
If a busnut has their systems, personal wetware and equipment, up to snuff, and wants to dispense with the duplication, we are free to do that.
Or, boldly going forth in ignorance in either direction, or some other one?
This isn't a religion, it's a hobby. There's more than one way to do things...
Happy coaching!
Buswarrior
Maybe one of these lithium ion battery jumpers rated for coach engine might be a consideration. They're very compact.
I haven't bothered to read through all the responses but I did just this years ago. My starting batteries are entirely made up of deep cycle AGM batteries. Never been a problem in the three years I've run them. Do what works for you.
Mine are 2-8d deep cycle, with the Vanner to pull the 12 volt loads. Previous owner was talked into removing the big alternator completely with no replacement. Currently, house and start batteries get recharged by the generator or plugging into shore. Has worked ok so far. Generator has it's own start battery, and I have switches and relays to boost start or gen batteries from house batteries.
I use 6 of the 6 volt golf cart batteries for the house and I thought I had 2 group 31's for the start batteries. I had to replace the start batteries today and when I took them in the guy told me they were deep cycle ones. It turns out the date on them was 9 years old. The only difference in the two types of batteries are the thickness of the separators inside. I replaced them with start type batteries because they were $55 cheaper each. If I get 9 years out of these I will be happy but I probably won't. Five years seems normal. So it turns out the deep cycle ones were working fine for all those years as a start type. Sure changed my thinking on using deep cycle type for a start application. The place where I bought them only sells batteries for many many years so he knows what he is talking about.
The battery on our genset is an 8D deep cycle from Napa. When I first got this bus, that battery was also serving as the house battery, hence the larger-than-necessary battery to start the Perkins.
Sounds like we're talking about two different but related issues here. One is whether or not deep cycle batteries can be used as start batteries. Apparently we have evidence they can.
The other issue is how much redundancy each of us feels comfortable with (or without). Some prefer separate house and chassis system, others are okay with combined systems. Apparently both can be made to work just fine.
Sorta depends on your paranoia level maybe? How many redundant systems do you need? I mean you can go all the way down to a small pull cord generator and if it starts reliably that can get you up and running. Or, if you are more relaxed, you can always drive off in the toad and go buy another battery or two when you have to. Or maybe your bicycle has a basket to carry one...(yeah, wouldn't THAT be a trip!)
I do like the concept of making fuller use of all your batteries, but I absolutely despise going to start the rig only to find it won't turn over. BTDT and hated it. Hated it so much that even once is too much. So, separate chassis batteries for me.
Jim
Same here Jim. If you run the one set does all down too far you are done. Murphy's Law says it will happen when you least expect it to no matter how diligent you are in watching the battery levels. More money but peace of mind is priceless. Even though I had deep cycle start batteries (not intentional) I still had a separate house system.