How to make a cheap isolated dual-battery setup for $50

[32vsnake]

Quick question,
If the solenoids generally draw around 1amp; then why does the solenoid to ignition source require 12g wire?


Thanks

 

[dlichterman]

Quick question,
If the solenoids generally draw around 1amp; then why does the solenoid to ignition source require 12g wire?


Thanks

You could probably get away with a smaller gauge(I think I used 14 since I had 14awg) but just make sure it is something strong enough that won't tear open and short.

 

[dwh]

Quick question,
If the solenoids generally draw around 1amp; then why does the solenoid to ignition source require 12g wire?

Heh...good point.

Um...lemme try to save evldave from having to sober up and figure out a good BS answer for that one.

Sunspots (okay, prolly only BOFH fans will get that one).



Well, if you are tying into a circuit that has been fused for 20a, then you need wire that can handle 20a, so that the wire won't melt before the fuse does if there is a short. If you're tying into a circuit that is protected by a 15a fuse, then you can get away with #14.

 

[josh18657]

So here is my plan and I am looking for any input so I do this right the first time around.

I want to use 2 batteries, obviously. 1 will be a regular automotive battery, the second would be a deep cycle battery.

Connected to the regular battery will be the starter, alternator and solenoid only.
The factory fuse block, under the hood would be connected to the 2nd deep cycle battery along with the solenoid and any other devices I add later

My reasoning for this is I sit in my vehicle quite a bit at work and it would be nice to be able to listen to the radio with the engine not running and not worry about draining the starting battery.

Now I would like to be able to charge at least the deep cycle battery while parked near a generator so what would you experts suggest for this?

 

[dwh]

Now I would like to be able to charge at least the deep cycle battery while parked near a generator so what would you experts suggest for this?

A battery charger.



I spotted one at Lowe's the other day that caught my eye. So I did some Interwebs research and I think I'm going to go back and buy one.

http://www.baccusglobal.com/stanley/bc1509.php


15a, 3-stage (I think it might actually be doing PWM), desulfation mode, temperature compensated (internally, not remote sensing) and it compensates for voltage drop on the supply side (might be good if the generator is loaded down or not holding voltage steady). Also has some sort of alternator test ability and a quick charge boost mode to get a vehicle with a dead battery started. They also make it in 25a and 40a.

50 bucks at Lowe's, a bit less on Amazon.


I've been avoiding going to a modern digitally controlled charger because they have a rep for not wanting to charge a battery with too low a voltage, but this one I guess you can work around that by pushing the desulfation button and letting it pulse the battery until the battery voltage comes up enough to accept a proper charge.

Twice the amps and less than half the price of the Battery MINDer (which I've almost bought a dozen times but kept backing out because it's only 8a).

 

[josh18657]

Is it ok to charge a batter while it's still in use powering the radio or a small tv?

 

[graynomad]

Yep, the only difference is that the voltage will go way over the nominal 12v to around 14v at times, this is no different to using a radio while driving and any gadget that is designed for 12v should handle it. There may be something around that is not happy with 14v but I doubt it.

 

[josh18657]

Awesome, thanks for the great thread with quick replies

 

[wrcsixeight]

Is it ok to charge a batter while it's still in use powering the radio or a small tv?

This is dependent on the charging algorithm of the charger.

Some of them will go well over 15 volts, and this range can indeed threaten some electronics.

My Schumacher sc2500a will go over 16 volts. Lots of schumachers will. Most manual chargers will if given enough time.

Also if using a radio while charging, there is the possibility of electrical noise coming through the speakers or reducing reception.

Rv converters are designed to be power supplies and battery chargers, but they are not ideal battery chargers despite their claims and marketing mumbo jumbo.

If you need a power supply, I'd recommend something designed for such duties. These can charge batteries too, and have an adjustable voltage pot which can take battery voltage to 15.5v for manual equalization.

http://www.amazon.com/MegaWatt-S-35...Supply/dp/B00JZBE97U/ref=cm_cr_pr_product_top

So Not automatic 3 stage charging, but 3 stage chargers or the 5 stage or the 8 stage chargers available are compromises to not overcharge a battery, while claiming to fully charge any given battery, which they do not do well. But people rarely actually verify with a Hydrometer, and believe the "full charge" light instead, which is wrong 95% of the time, but it is a chest thumping self satisfying full charge light.

 

[mapper]

So here is my plan and I am looking for any input so I do this right the first time around.

I want to use 2 batteries, obviously. 1 will be a regular automotive battery, the second would be a deep cycle battery.

Connected to the regular battery will be the starter, alternator and solenoid only.
The factory fuse block, under the hood would be connected to the 2nd deep cycle battery along with the solenoid and any other devices I add later

My reasoning for this is I sit in my vehicle quite a bit at work and it would be nice to be able to listen to the radio with the engine not running and not worry about draining the starting battery.

Now I would like to be able to charge at least the deep cycle battery while parked near a generator so what would you experts suggest for this?

So...I'm going to need to step this back a bit. I have an elementary question. I'd like to setup a dual batt system as outlined waaaaayyyy back on page 1. Can I, like josh wants to do, use an AGM Die Hard Platinum as my house battery but keep my standard automotive battery for starting? Or do I need to switch to an AGM for a starter battery too? If not, what type of "house" battery should I be looking to use inside my van.

I'd rather just keep a standard auto battery for the economy of it. Thus far, in over 5 years, I've never had a problem with a standard auto battery. I don't put a high demand on it and I only want a house battery to begin adding minimal camper accessories (LED lights/fan/maaaaybe firdge) that are isolated from the starting circuit.

 

[graynomad]

I've done that (AGM for house, starter for car) many times, I suppose in theory you are charging two different styles of batteries in parallel and that's not recommended, but it works just fine. If you also have a solar panel the house battery will get a much better charge.

A proper DC/DC or Alt/DC charger would be much better as they are tuned to properly charge the house battery, I'll use one of them next project i think.

 

[DiploStrat]

Battery Types

Some comments:

-- Depending on the age of your vehicle's starter battery, it may well be an AGM, or some other type of sealed battery anyway.

-- For a camper battery you want a deep cycle battery. That battery may be open cell (less expensive) or AGM (less maintenance). There is nothing about an AGM that makes it particularly suitable for use as a camper battery.

-- Most vehicles never run long enough to fully charge a large camper battery bank, so a B2B or an A2B may not be worth it. B2B's DO have one great advantage, they can boost the charge voltage (at the cost of amperage) in an install where the basic wiring is not quite as large as it could be.

-- Vehicle alternators, combined with sufficiently large cabling, are great for providing lots of amps for the boost charge stage. There after, you probably need solar or shore power to get a large (say 200 Ah or more) bank through the hours of acceptance charge required to reach a full charge. So it is very unlikely that you could so mismatch your battery types as to create a real problem.

What is wrong with B2B's and A2B's?

-- They are big, expensive, and produce a lot of heat.

-- They are not bidirectional (One exception is the combination of a CTEK D250S and a SmartPass.)

Are they for you? Just depends. In my case I dismounted my A2B and with with something simpler.

 

[mapper]

Thanks guys. I was also reading a few other threads and one statement, in particular, made sense to me.

DWH stated in another thread (though I summarize and maybe bastardize the point to an extent):
The economy of "perfectly" maintaining a house battery to achieve the full design life is not practical. Meaning the cost/benefit ratio of regularly obtaining a full state of charge, FOR MY INTENDED NEEDS, is not there. Therefore consider buying a house battery with the intention that it will be abused and need more frequent replacement, on the order of 2 years vs. 6 years theoretical life. Meanwhile, take good care of your starting/chassis battery as that is the one you really need to rely on.

Since my situation places demands on a house battery that can be defined as "comfort" vs "necessity" I think this philosophy suits my needs well.

 

[mapper]

Here is the direct quote
From this thread:
http://www.expeditionportal.com/forum/threads/127108-Dual-Battery-not-rocket-science

I use a starting battery for chassis use, and a deep cycle for aux loads. (In other words - the right tool for the job.) They are not the same size, age, type, manufacturer, etc. - and it doesn't matter. They both want to be charged to 14v+ and the truck's charging system does hold the electrical bus at 14.5v when engine RPM is above idle.

Since they are separated when the engine is off, it doesn't matter that they don't match and the deep cycle will certainly wear out faster, because it's doing all the work of supplying the aux loads while the engine is shut down. The chassis battery does nothing while the truck is parked.

I've worn out and replaced 3 deep cycle aux batteries in the (uh...can't remember offhand...6 years or so) since the last time I replaced the starting battery. Next time I replace the aux battery, I'll probably do both since the chassis battery is about due to be replaced anyway.

(And yes, 3 deep cycle batteries in 6 years is a lot of batteries, but I'm semi-retired and use my camper a lot. I also consider the house battery in MY camper to be disposable and so I just beat the unholy crap out of them by draining all the way, not always recharging ASAP and not always recharging them fully when I finally do get around to charging them. Basically, what every expert tells you not to do - I do regularly. I don't make a hobby or a career out of babying, nursing and nannying batteries. So personally I just buy cheap deep cycle batteries and hammer them into the ground and replace them regularly.

But, also consider that those 3 batteries cost a total of...I dunno...maybe 250 bucks. About the same price as buying one good AGM deep cycle and taking care of it to make it last while damn near full-time living in the truck. And even if I did spend the money and take the time to baby a good battery - would it last for 6 years of almost full-time use? Unlikely.

And I ALWAYS DO spend the money to get a good quality chassis/starting battery, because I want the truck to always start, and I'm not going to abuse that battery anyway.)

 

[dwh]

Did I say that? Jeez...musta been drunk...

Nah, I was serious. I notice now, reading that quote, that I left out another key point...

To get the full life from a quality battery, not only requires taking good care of it, but it also requires NOT draining it below 50%.
I don't have that limitation beating the crap out of cheap deep cycle batteries.
So I can get 100 amp*hours out a cheap 100ah battery, whereas to get the same usable energy budget out of a good battery - I'd need TWO 100ah batteries.