Dual battery setup questions

Method

New Member
Hi all,

I have spent hours searching Google for the best way to set up a dual battery system and figured this is probably the best place to ask questions as there is so much conflicting information online.

First things first, I don't own a 4x4. I have a light truck which runs off a 24v system. I purchased a DC DC charger a long time ago and plan on putting a single 12v battery to run my accessories off. I just bought a fridge which is the main reason for the need of a dual battery setup. I will add lighting to my toolboxes which will run off the accessory battery but my main question is that I also have an engine driven welder and diesel compressor on my truck. I was planning to run both the welder and compressor off the accessory battery which would eliminate the need to have the two additional batteries which are currently on the welder and compressor. I don't use these every day, sometimes not for weeks on end. My truck never runs when I am using the compressor or welder. Would using the accessory battery to start these be an issue for the entire dual battery system? The welder has its own alternator but the compressor does not.

I was also wondering what the best way to run large cable to and from the dc dc charger is? I have plenty of welding cable suitable for up to 600A of current I was hoping to use for most of the main runs and then 8g for my accessories. The terminals on the DC DC charger seem too small to connect such large cable to.

Any help would be appreciated. I am still trying to plan the best way to set this up.

Paul.
 

Petunia

Well-Known Member
Mixing 24V, start and deep cycle, 12v, charge and no charge?

I was planning to run both the welder and compressor off the accessory battery which would eliminate the need to have the two additional batteries which are currently on the welder and compressor
Technically these need a ''Start'' battery lots of guts up front, short n sharp high amp burst of power, then recharged, the welder will recharge so no problem there.
It is frowned upon using a deep cycle as a start battery as these provide power over a long period.
The diesel compressor most likely only need power to a fuel on/off shut stop device? unless you have a pull cable to stop? It will by design most likely use sweet not much power while running? The question is how is it recharged?
Would using the accessory battery to start these be an issue for the entire dual battery system? The welder has its own alternator but the compressor does not.
Yes and No, depending on the type of battery? These units need a ''start'' battery. As most dual battery set ups use a deep cycle for extended usage over time, not cold cranking amps, one may kangaroo edward the deep cycle battery?

I currently use a ''hybrid'' [start 910cca, 110Ah deep cycle capacity] along with a 770cca regular start battery. This system has proven itself over the last 6 years [invoice date- 20/06/14] so to the Negative Nellies, it works! The problem I now face is age and the fact this particular brand is no longer imported. I went searching the supplier who agreed the battery was a [bleep] good battery, but as they had to import a pallet of them to only sell 5 because no one was going to use a non common brand.
I was also wondering what the best way to run large cable to and from the dc dc charger is? I have plenty of welding cable suitable for up to 600A of current I was hoping to use for most of the main runs and then 8g for my accessories. The terminals on the DC DC charger seem too small to connect such large cable to.
Welder cable is the ducks bottom in my opinion, couldn't wish for better, fine multi stranded able to carry lots of current.

8g is more than adequate [in my opinion] for accessories, as most low draw accessories may draw fairly low current eg 5watts of light draws [nominal] >0.5amps, 2 100watt spot lights draw [nominal] just over 15amps as an example.

I would terminate your welder cable to a bolt/nut in a busbar to accommodate the larger terminal, then use a smaller nut/bolt combo to connect suitable size wire/terminal to the dc/dc unit. A simple busbar can be made from copper pipe flattened and a nylon kitchen cutting board cutup for insulation, backing.

Now the dilemma of start and run batteries? I would consider using one of the truck batteries as a start battery for the welder and compressor? But that would need very serious thought as a positive and a negative are connected to form 24v, back feeding the 12v charge would infact just go BanG!!
.A hybrid totally feasible and probably the preferred method, giving start ability, run ability, and charge via dc/dc very simply. [I'm yet to find an alternative for my ageing hybrid][if the supplier still had them I would buy 2, I'm that impressed]

I can't think now, ask questions no matter if they seem trivial. :cool:
 

Method

New Member
Mixing 24V, start and deep cycle, 12v, charge and no charge?
The DC DC charger does 12v charge from 24v input, so I figured this was the best option as there are more 12v accessories than there are 24v if I ever want to add anything to the setup. The only advantage of 24v from what I can find is reduced cable size, so the benefits don't seem that great keeping it all 24v.

Technically these need a ''Start'' battery lots of guts up front, short n sharp high amp burst of power, then recharged, the welder will recharge so no problem there.
It is frowned upon using a deep cycle as a start battery as these provide power over a long period.
The diesel compressor most likely only need power to a fuel on/off shut stop device? unless you have a pull cable to stop? It will by design most likely use sweet not much power while running? The question is how is it recharged?
I bought a Katana YTX20L-BS battery for the compressor, I left the ignition on the compressor once and within a few days the battery was completely dead which was odd.. I since charged it up and it worked fine, but the compressor doesn't seem to charge it? If I connect my jump pack or jumper leads to the battery and start the compressor, even after 10 minutes of leaving the leads connected (not jump pack) the compressor turns off as soon as the leads are disconnected (or as soon as I disconnect the jump pack)

Yes and No, depending on the type of battery? These units need a ''start'' battery. As most dual battery set ups use a deep cycle for extended usage over time, not cold cranking amps, one may kangaroo edward the deep cycle battery?

I currently use a ''hybrid'' [start 910cca, 110Ah deep cycle capacity] along with a 770cca regular start battery. This system has proven itself over the last 6 years [invoice date- 20/06/14] so to the Negative Nellies, it works! The problem I now face is age and the fact this particular brand is no longer imported. I went searching the supplier who agreed the battery was a [bleep] good battery, but as they had to import a pallet of them to only sell 5 because no one was going to use a non common brand.

Welder cable is the ducks bottom in my opinion, couldn't wish for better, fine multi stranded able to carry lots of current.

8g is more than adequate [in my opinion] for accessories, as most low draw accessories may draw fairly low current eg 5watts of light draws [nominal] >0.5amps, 2 100watt spot lights draw [nominal] just over 15amps as an example.

I would terminate your welder cable to a bolt/nut in a busbar to accommodate the larger terminal, then use a smaller nut/bolt combo to connect suitable size wire/terminal to the dc/dc unit. A simple busbar can be made from copper pipe flattened and a nylon kitchen cutting board cutup for insulation, backing.
I had thought of terminating the large cables at a busbar so thank you for clarifying that and the suggestion of making the busbar is handy!

Now the dilemma of start and run batteries? I would consider using one of the truck batteries as a start battery for the welder and compressor? But that would need very serious thought as a positive and a negative are connected to form 24v, back feeding the 12v charge would infact just go BanG!!
.A hybrid totally feasible and probably the preferred method, giving start ability, run ability, and charge via dc/dc very simply. [I'm yet to find an alternative for my ageing hybrid][if the supplier still had them I would buy 2, I'm that impressed]

I can't think now, ask questions no matter if they seem trivial. :cool:
I thought that using one battery to start either the welder or compressor would destroy the longevity of the start batteries as one would be discharging more than the other every time I start the welder/compressor. I will look into the hybrid batteries to see what I can find. I was thinking of using a caterpillar lead acid battery. We have several excavators/bobcats and at times the occasional machine has sat around for 6 months without being started and starts perfectly every time. We also get an average of 5-7 years out of these batteries.

My other thought was to leave the two batteries on the compressor and welder and purchase one big battery (can't be super large as I am fitting the battery, dc dc charger and fuse box etc in an under-tray toolbox) and connect the new accessory battery in parallel with the other two batteries essentially having 3 batteries in parallel. All three are different sizes, but the same voltage so I couldn't see any downside to this?

My fridge tool-box arrived yesterday, so I haven't even had a chance to read the instructions of the Engel fridge yet but if I plugged the fridge into 240v mains when home, do I need to disconnect the 12v supply or do they automatically switch over?


Thanks for your quick response!
 

Petunia

Well-Known Member
so the benefits don't seem that great keeping it all 24v
At some stage you would have to transform 24 to 12 ....... for the one thing

I bought a Katana YTX20L-BS battery for the compressor, I left the ignition on the compressor once and within a few days the battery was completely dead which was odd.. I since charged it up and it worked fine, but the compressor doesn't seem to charge it? If I connect my jump pack or jumper leads to the battery and start the compressor, even after 10 minutes of leaving the leads connected (not jump pack) the compressor turns off as soon as the leads are disconnected (or as soon as I disconnect the jump pack)
That answers the question, it has an electric fuel on/off 'something'. Small engines [elec start] should have a rudimentary alternator under the flywheel how much they generate I do not know. Katana .... standard charge is 1.8 amps for 5 to 10 hours, OR a quick charge of 9amps for 1 hour. [more on this battery later]
A simple test of is the alternator alternating, measure voltage at the battery terminals with engine off then running, running should be more than not running. How much more? I don't know [1 to 2? ]. None of ours here are elctric run [pump jacks], they are started with a battery, by hot wiring, then run out of diesel, and when they don't start the ute jumps them, the battery comes home for a charge. [''we don't do simple here'']

making the busbar is handy!
I make terminals from copper pipe as well at times, it's 2 hours to somewhere and back to get a terminal, a piece of 1/2 and 5/8 copper pipe hangs on the laundry wall plus other odd sizes from odd places, I keep eyeing off the gas pipe it's 3/8.

I thought that using one battery to start either the welder or compressor would destroy the longevity of the start batteries
True, yet the compressor won't take much to start, and not knowing the welder, that could be anywhere up to a V8, in the days of old nothing under a holden red motor would run a welder, today a generator and an inverter welder on a shoulder strap.

I was thinking of using a caterpillar lead acid battery
I did a half dead brain look at Cat batteries one night the thought has been in my head, I need do it again, I'm not going to be asked ''Whats it for'' to reply with duh, a [beep] toyota ya wally why do you think I'm here?

My other thought was to leave the two batteries on the compressor and welder and purchase one big battery (can't be super large as I am fitting the battery, dc dc charger and fuse box etc in an under-tray toolbox) and connect the new accessory battery in parallel with the other two batteries essentially having 3 batteries in parallel. All three are different sizes, but the same voltage so I couldn't see any downside to this?
Katana, again ... that is rated at 270CCA, the welder?
I can tell you from experience with two start batteries one 770, the other 910, the 910 is behind the seat, it goes into a 200amp solenoid for connect/disconnect via two 4ga wire on both + and - [i don't got welder cable] then to the 770 [4 4ga wire, again] then the toyota wire crosses the front of the engine and down to starter. When both are charged properly the starter is almost jumping out the bonnet.

So depending on what battery is on the welder, and what you buy? To hook all three in parallel I would imagine you may launch the compressor starter into orbit? The compressor obviously starts with only 270CCA, putting not one but two in parallel that little starter is going to rev its ring off.

Engel fridge
I still run a 3way gas/12/240 it is possible to run on all 3 at once, OOPs. I have heard/read that engel are automatic changeover, but I know sweet not much other than what I have heard.

Okay, brain drain. :cool:
 

Method

New Member
That answers the question, it has an electric fuel on/off 'something'. Small engines [elec start] should have a rudimentary alternator under the flywheel how much they generate I do not know. Katana .... standard charge is 1.8 amps for 5 to 10 hours, OR a quick charge of 9amps for 1 hour. [more on this battery later]
A simple test of is the alternator alternating, measure voltage at the battery terminals with engine off then running, running should be more than not running. How much more? I don't know [1 to 2? ]. None of ours here are elctric run [pump jacks], they are started with a battery, by hot wiring, then run out of diesel, and when they don't start the ute jumps them, the battery comes home for a charge. [''we don't do simple here'']
I have tried to find an exploded view of the compressor but had no luck. It is a compressor from Boss Compressors. They sell a stator on their web site but I am yet to have a good look as to where this is on the motor, so you are correct about it having something. Will have a look during the week if time permits

True, yet the compressor won't take much to start, and not knowing the welder, that could be anywhere up to a V8, in the days of old nothing under a holden red motor would run a welder, today a generator and an inverter welder on a shoulder strap.
It is a Cigweld engine driven welder/generator with a Kubota 3cyl diesel motor. I will check the battery to see its specifications as I replaced the battery maybe 4 years ago and have no idea what I replaced it with.

On the Cat battery, I am surprised no one has used them or tried using them for these applications. They are very well priced for the performance we get out of them with the machines.

Katana, again ... that is rated at 270CCA, the welder?
I can tell you from experience with two start batteries one 770, the other 910, the 910 is behind the seat, it goes into a 200amp solenoid for connect/disconnect via two 4ga wire on both + and - [i don't got welder cable] then to the 770 [4 4ga wire, again] then the toyota wire crosses the front of the engine and down to starter. When both are charged properly the starter is almost jumping out the bonnet.

So depending on what battery is on the welder, and what you buy? To hook all three in parallel I would imagine you may launch the compressor starter into orbit? The compressor obviously starts with only 270CCA, putting not one but two in parallel that little starter is going to rev its ring off.
I never even considered this o_O Thank you for bringing it to my attention. What I might do is have an isolator on the negative of the lead going to the welder and another going to the negative of the compressor which I could turn off prior to starting either one of the two. Would you see any issues in doing this? That way I should have the added advantage of the extra Ah as well as have all batteries charge off the DC DC charger when they are not isolated. I will have to remember to isolate the batteries prior to starting either of the two.... remembering is the hard part >.<
 

Petunia

Well-Known Member
Would you see any issues in doing this?
Short answer, yes.
I got into a mexican standoff with an Audio guy when designing my battery system I wanted cable, only cable, and just cable. Where can I get good thick cable? I said to myself, A:- welding supplies, B:- Audio Amp DoofDoof cable. I chose doofdoof option and proceeded to the audio store, well, I asked for, then came that ubiquitous question ''What's it for?''

After saying truthfully what the purpose was, the ''indignant I am a audio professional lecture'' began, ''you are making more resistance'' ....... YES!! ok keep your hair on. I Want EQUAL resistance, all he kept quoting was more resistance several times, I got hot under the collar and walked out, No Sale, suck eggs Mister! The cable can retail over $10/m I want 16m to start with, your loss!

I disregard 'resistance', most times, simply, I'm not making highly critical sensitive parts for a 27 year space mission, I'm just a dude that thinks outside the box. [my diff breathers came from the irrigation shop, my oil filter/fuel filter/s come from the massey ferguson dealer]
In solar parallel battery banks, [2 ~ 102] connections, there seems to be this underlying importance of all cable lengths are equal, Logical Dr. Spok, equal resistance. To me this means connecting 2, or more batteries, together in a system every cable that connects one battery to another is of equal length, both the positive & negatives. < This becomes apparent when taking power from/recharging the bank. [going back to the original thought of using one battery fro the 24v as a 12v starter depleting one only]

If you take the easy option hook + and - to the first battery, the one on the other end will fail sooner or later, + goes in the first battery, then the - comes out the last battery, eg:
Bat Trees.JPG

The principle is similar for any number of batteries of the same type/rating. Now can you do that with 3 vastly differing batteries? Again the dirty word, ''resistance'', each battery in itself will have a different internal resistance. Electricity is a lazy sod, taking the path of least resistance, one battery having less/more resistance than the others will be a hole in the bucket or a giant heater depending on how they are wired, yes parallel still, but depending on 3 separate earths versus one common earth?

It was a simple setup, wasn't it? Who started all this thinky rubbish? :cool:
 

Decca

Member
I think I have a grasp on what you want...'Correct me if on wrong track.

To begin with; I would not tap 12V off the truck's 24V battery.
And only parallel up identical batteries i.e. same brand, capacity and age... and as per drawing above. Any more than 2 batteries and it gets very difficult to balance out current drain and charging... but not impossible.

I can see no real issue with the accessory battery being connected to Welder and Compressor starter motors, and your fridge, lights etc...although starting motors and running fridges requires different battery types for optimal perfomance it is do-able.

The only link between the truck's batteries and the other battery (for welder,comp,fridge) should be the charge circuit.
Re charging the 'other' battery....You say you have a DC DC charger.... does it have two inputs.?
Some have an input for the alternator feed and one for the solar panels.
If so.. use the solar panel input for the truck's alternator output, and the alternator input for the welder's alternator.

Re cable size... I would use 8G between DC DC charger output and the Accessory battery. Inputs to the charger can be lighter


battery in parallel with the other two batteries essentially having 3 batteries in parallel. All three are different sizes, but the same voltage so I couldn't see any downside to this?
Not recommended. different batteries will have different discharge and charging rates. And some may not fully charge
You are not even supposed to mix the alkaline batteries you have in your torch...

To hook all three in parallel I would imagine you may launch the compressor starter into orbit?
No. batteries in parallel will have same votage as a single battery.. but a lot more capacity.
If they were connected in series you'd have 36v spinning your 12v starter motor

A simple test of is the alternator alternating, measure voltage at the battery terminals with engine off then running, running should be more than not running. How much more? I don't know [1 to 2? ].
Alternators should charge batteries at around 14.2 ish volts

Apologies if I have wafted on :)
 
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Petunia

Well-Known Member
No. batteries in parallel will have same votage as a single battery.. but a lot more capacity.
If they were connected in series you'd have 36v spinning your 12v starter motor
You are correct, but ''Start batteries'' are rated in ''CCA Cold Cranking Amps'' the higher the CCA the more ''guts'' the battery has. Think Lawn Mower when referring to a small engine on a compressor that uses in essence a motorcycle battery.
Alternators should charge batteries at around 14.2 ish volts
Again you are correct, but again think Lawn Mower, A magnet or several glued under the fly wheel passing a coil of copper wire, with or without a rectifier?
 

Method

New Member
I haven't had a chance to test the compressor charge status as of yet. Taking into consideration your comments about different battery types and their charge rates, resistance etc. It would be best if I just left the welder and compressor batteries as is, excluding the batteries from the dual battery setup all together.

In reference to your comment about pulling 12v off the 24v system, the DC DC accepts a 24v input and will charge a 12v battery which will be the battery I am yet to purchase. If I had of known earlier I should have bought the one with a solar input, I thought.. I'll never use solar so why bother smh!!

In regards to AH, how accurate are these numbers? Would a quality 70ah battery keep up with a cheaper 100ah battery?

I only have approx 350mm l x 190mm w x 240 h to work with in my undertray toolbox as I'll be mounting the DC DC charger in there with the bus bar and fuses etc.a. A battery of this size would be optimal in order to neatly fit everything else in the same box.

I ran two conduits from the batteries tonight, beneath the tray along the chassis rail. 1 x 35mm conduit and 1 x 25mm conduit for the main cables. I'm not sure of the exact cable sizes but one is approx 10mm and the other spare cable I had is approx 18mm. Overkill I know but it didn't cost me anything. Question... With cable this size, obviously capable of taking a continuous load of >200amps and the larger >500amps do I really need to fuse both ends of the positive cable between the main batteries and DC DC charger? I would assume it's still a good idea as I'll be terminating the 00000000 size cable down to 6/8mm before connecting it to the DC DC charger so the fuse would go in the 6/8mm run? The other end though??

Any recommendations on a suitable battery? General CAT were what I was looking at, their AGM batteries seem to have a low AH rating unless you go super large like 500mm in length. This is what made me raise the question re the quality and accuracy of the AH ratings. I see the cat AGM batteries are similar size to some others that are rated almost double the AH? According to this chart:
CAT Batteries

Prior to doing all of this my plan was to purchase the cordless power supply from Milwaukee but covid has delayed the release by months now. It would have been so convenient to just put the power pack inside my toolbox, be able to run a microwave, fridge etc etc all day long and just plug it into 240v to charge every few nights, it would have made life much simpler :p
 
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