Using simple battery switch to charge house circuit?

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TravelingTuttles
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Using simple battery switch to charge house circuit?

Post by TravelingTuttles »

First post! But lurking for a few months since my wife and I bought our 1982 712W. We're on our way to living in it full time. Here's the question:

Will I cause undue/unusual harm to the stock alternator by using a simple battery switch to charge a bank of house batteries? I'd like to be able to start the truck, let it run for a few miles to top up the truck batteries, and then move the switch to tie in the house batteries so they can charge as well. I'm planning on building a 24v house circuit that charges off 2x100w solar panels and off the alternator. I'd like to use a simple switch, but I'm worried about damaging the 20amp relay that protects the regulator/rectifier, as well as over working the alternator. Are these legitimate concerns? I am comfortable with needing to be constantly mindful of the switch's position, and would rather trade convenience for simplicity.

Thoughts? Thanks in advance.
1982 712W - "Little Foot"
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Jimm391730
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Re: Using simple battery switch to charge house circuit?

Post by Jimm391730 »

Never, ever "disconnect" batteries while the engine is running. This means that switching between batteries can be done, but your switching set up must ensure that you connect the second set of batteries before disconnecting the first set. This is the reason for the relay that keeps the ground connection even if you inadvertently open the disconnect switch. With the disconnect switch closed the relay does not carry any current, so you should not have to worry about its rating.

Other than the above, you generally won't hurt anything by using the alternator to charge an additional set of batteries. The alternator is limited to 30 amps by its design (assuming it is working into ~28 volts of batteries). High currents make more heat and are harder on things but it is generally not possible to significantly overload the alternator -- "overloading" just causes the voltage to fall which reduces the current to the batteries.

I have dual 100 Ahr batteries for my "house" batteries; each is typically charged independently by its own solar panel and separate charge controller. This keeps them equally charged, no matter what. But a few years ago I had been camping for over a week and had been draining them more than the panels could recharge them; they were down to about 11 volts. When I left my camping spot I tied them into the chassis batteries (in parallel) which pulled the voltage down to about 25 volts (while running) and it took 4 HOURS to finally get the voltmeter to get back to ~28V. But the alternator suffered no ill effects.

In my 712W the box was powered by a heavy connector to the socket behind the passenger seat; I keep this unplugged to keep the chassis and house systems separate. But I can plug it in when needed, as I did after camping. I have increased my solar capacity (was 2x 55W, is now 2x 100W) and set up the panels so they can be tilted towards the sun to improve the power from them. This should now keep up with my Engel fridge and lighting where the lower power panels did not, before.

Best of luck,
Jim
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rmel
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Re: Using simple battery switch to charge house circuit?

Post by rmel »

My recommendation would be to list out all the appliances you want to power on the House side of the "W".
My hunch is that you will find that your choices for 24V will be limited, but 12V will be more extensive and cheaper.
The yachting community figured that out and typically run with a 24V to 12V solution. I realize that there is compatibility
with a 24V Aux battery with the 24V Pinz, but this is not a good reason to go that route IMHO. If you go 24V I would bet
that you end up with a 24V to 12V converter hanging off this system too, just more complicated.

I would also recommend not using a switch but rather set this up so that the charger has the smarts for you. There are
chargers on the market that can take as input Solar (MPPT) or a 24V alternator and happily flip between the two sources.
This is how I am configured; 4 Yellow Tops @ 12V, with 200W Solar -or- the 24V alt as a charging source -- lots of comm's
gear, NAV, and computers.

The best product on the market (IMHO) for this is from REDARC from the land of OZ. There are distributors in AU that
can ship direct to you (PM me if your interested). You could also build your own with a MPPT to 12V charger and a 24V to 12V
charger but you will need solenoids to select these sources and it's just not as "smart" as the REDARC.

cheers,

ron
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712MK

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Ian
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Re: Using simple battery switch to charge house circuit?

Post by Ian »

Nothing wrong with a simple switch, that is what I use. The only real concern to keep in mind, is you must remember to turn it off at night! Very easy to forget and find in the morning not only are the house batteries run down, but the engine ones too!! With that in mind, I invested in an expensive 'smart' relay a couple of years back (not a REDARC). you could program a time delay into it before it cut in and also adjust the cut in/out voltages. All very good. Apart from it gave me no end of trouble and went back to the supplier twice for warranty repairs before I binned it. It would connect the 2 battery banks, but only allow a tiny current through it, so took an age to charge the house bank. Both times it came back, it was 'repaired' only to fail again a few months later.
I went back to the simple isolator switch. Cheap, simple and reliable. Just need to make sure I remain 'reliable' in turning it off at night :D :D
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Re: Using simple battery switch to charge house circuit?

Post by TravelingTuttles »

Jimm, Rmel, and Ian,
Thanks for the advice. Now I'm reconsidering everything about my battery and solar setup plans. Luckily I'm reconsidering before I bought!
Jimm391730 wrote:Never, ever "disconnect" batteries while the engine is running. This means that switching between batteries can be done, but your switching set up must ensure that you connect the second set of batteries before disconnecting the first set. This is the reason for the relay that keeps the ground connection even if you inadvertently open the disconnect switch.
Yeah, I totally get that. For that reason I was looking at the E-Series 4 Position battery switch by Blue Sea Systems. It touts a "make-before-break" style that engages the next choice of battery before breaking the circuit on the previous choice. I've used other products of theirs on other vehicle conversion and was happy with the build quality, and the price point isn't crazy either.
rmel wrote:My recommendation would be to list out all the appliances you want to power on the House side of the "W".
My hunch is that you will find that your choices for 24V will be limited, but 12V will be more extensive and cheaper.
The yachting community figured that out and typically run with a 24V to 12V solution. I realize that there is compatibility
with a 24V Aux battery with the 24V Pinz, but this is not a good reason to go that route IMHO. If you go 24V I would bet
that you end up with a 24V to 12V converter hanging off this system too, just more complicated.
My house side appliances:
  • Whynter 12v/24v/110v refrigerator
    Cell phone USB chargers (24v easy to find at most any store. A lot, but not all, of the cigarette-lighter-style chargers accept 24v.)
    Lights? Maybe.
    Inverter for light use, occasional 85W laptop charging.
What do you think?
Ian wrote:Nothing wrong with a simple switch, that is what I use. The only real concern to keep in mind, is you must remember to turn it off at night! Very easy to forget and find in the morning not only are the house batteries run down, but the engine ones too!!
I still may go this route, now that I'm a little more certain that a simple switch won't hurt the alternator or pose an overcharging risk. At least, from what I've gathered, the overcharging risk is small because the alternator isn't pushing much in the way of amperage.
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Jimm391730
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Re: Using simple battery switch to charge house circuit?

Post by Jimm391730 »

battery switch by Blue Sea Systems. It touts a "make-before-break" style
Exactly what you need; good to know that you know and understand what "make-before-break" is and means. But it may not be necessary, in that there may not be a need to ever disconnect the chassis batteries even if you need to charge the house batteries.

Looking at the specs of the Whynter fridge, it draws almost double what my Engel draws (at 24V, 2.5A vs the Engels 1.5A that I've measured). Assuming that it runs about the same percentage as my Engel, 200W of solar may not be enough to run it indefinitely. So being able to charge from the alternator is likely necessary.

You might consider a relay to connect the house batteries to the chassis; configure the relay (if it has an extra set of contacts) as a latching relay that is powered by the ignition switch. Start the truck, push a button to "latch" the relay to connect to the house batteries and they will get charged. But as soon as you turn off the key the relay unlatches, automatically disconnecting the house batteries. I would also recommend dual voltmeters in the cab for house and chassis batteries so you can monitor their status especially before connecting them (as their voltages will be essentially equal once they are connected).
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Re: Using simple battery switch to charge house circuit?

Post by TravelingTuttles »

Jimm391730 wrote: Looking at the specs of the Whynter fridge, it draws almost double what my Engel draws (at 24V, 2.5A vs the Engels 1.5A that I've measured). Assuming that it runs about the same percentage as my Engel, 200W of solar may not be enough to run it indefinitely. So being able to charge from the alternator is likely necessary.
The downside of our Whynter fridge is the power draw. I read some comparisons a while ago and it seems like our fridge uses nearly twice as much power as the competitors' offerings. The flip side, however, is that the construction and price are satisfactory. I'm REALLY hoping that 2x100 panes will be enough to power the sucker. For an non-electrical guy like me, it's tough to figure out how much power the fridge actually needs when it's running the compressor intermittently.

Also, in the last hour or so, we've decided to go with a 12v house circuit. The panels, connectors, wiring, and charge controller (no batteries or mounting hardware) came to ~$330. Not bad. In the end a lot of the motivation to go 12v was price. 24v charge controllers were pricey. Thanks, Rmel!

And Jim, I'm definitely going to need to charge off the truck system. Probably looking at powering a 110v battery charger off a 300W inverter (we want an inverter for the occasional laptop charging anyways). Here's my reasoning:
  • We want an inverter anyways, and it would need to be powered off the truck circuit.
    A 110v battery charger can charge any of the batteries separately for on the road maintenance.
    The truck batteries are protected by the inverter's low voltage cutoff (24v).
Are we dumb? Is this a bad idea? Is there an easier way?
Coincidentally these are all questions we asked ourselves before buying our Pinzgauer!
1982 712W - "Little Foot"
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rmel
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Re: Using simple battery switch to charge house circuit?

Post by rmel »

Well, wait till you see the bill for the REDARC charger :wink:
Although the exchange rate is in your favor. The good thing
about AU products is they typically are extremely well designed.

Oh! I have an ARB fridge, hardly ever goes on. In fact I first thought
it was busted then it went on after nearly a full day, and that puppy
was packed :) very low current draw and well insulated.

Funny thing with solar panels, you need da Sun :wink: this time of
year I get less and less then the cover needs to go on for the rainy
season (rainy I hope) -- then out comes the 110V battery charger.

Ya, the list will go on and on for more things to add, emcomm, computers,
nav, toss in a 50" plasma panel :) well, speaking from experience
anyway, it doesn't seem to stop.
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712MK

Driver: Ron // KO0Q
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Re: Using simple battery switch to charge house circuit?

Post by TravelingTuttles »

rmel wrote:Funny thing with solar panels, you need da Sun :wink: this time of
year I get less and less then the cover needs to go on for the rainy
season (rainy I hope) -- then out comes the 110V battery charger.
Oh man, you're telling me. Actually, I'm thinking my next upgrade might be to make that sun shine 24 hours a day!
1982 712W - "Little Foot"
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