Battery isolator

Mitsubishi Delica Camper vans, lift kits & other Delica Accessories!

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nxski
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Re: Battery isolator

Post by nxski »

I was meaning that I couldn't do what Tojo suggested since that requires a 300 amp isolator. When I finish working weekends I'll try to get together with Jay and figure out what to do with mine.
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Had: 1991 Mitsubishi Delica L300 SuperExceed, heavily modified (totalled by a drunk driver)
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lopar
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Re: Battery isolator

Post by lopar »

nxski wrote:I was meaning that I couldn't do what Tojo suggested since that requires a 300 amp isolator. When I finish working weekends I'll try to get together with Jay and figure out what to do with mine.
What is your intent of the isolator.......... is it not to isolator the secondary battery for running accessories so you do not deplete the main for starting?
The isolator would then only need to handle a charging current, normally much less than 30amps even.
Even if you wanted to add in the secondary for more capacitance during cold weather starting....... if 300amps is the starting draw and the batteries are equally charged and both in decent condition, you should never see more than 150amp draw from each battery, maybe upwards of 200 if batteries are imbalanced........
200 amp isolator should be more than adequate....... should through in a 200ish amp current limiter (fuse) to protect isolator, batteries and wires anyway.
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nxski
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Re: Battery isolator

Post by nxski »

The intent is to have the isolator on a switch so I can save one battery for starting and the other for accessories but still be able to flick a switch and start the vehicle with both batteries. I'm meeting up with Jay in the next week or so and I'll bring along the isolator and go through some possibilities.
Live the life you love, love the life you live...

Had: 1991 Mitsubishi Delica L300 SuperExceed, heavily modified (totalled by a drunk driver)
Have: 2011 Acura CSX manual, lightly modified
Want: Mitsubishi Pajero Evo

http://nes-design-construction.com
http://ca.linkedin.com/pub/nicolas-spurling/46/b48/924

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Johnny2Bad
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Re: Battery isolator

Post by Johnny2Bad »

rezdiver wrote:all the switch should have to do is energize a low current coil which closes the main contacts in a relay which carry a high current. a switch should never have to carry full load current if wired properly. most switches should handle up to 10 amps
[... snip ...]
.
The point of a relay is to use a very low current circuit to switch a high current circuit. So, you're absolutely correct that there is not much problem with an off-the-shelf switch, within reason.

However you should be careful if you use a switch in an automotive application without a relay. " ... most switches should handle up to 10 amps ..."

It is not necessarily true that most switches can handle 10A of DC. Generally switches are rated for Alternating Current (like in your home) and might be used, for example, to operate a lamp in your living room or a blender in your kitchen.

The Direct Current in your vehicle is not AC, however. With AC, there is zero voltage across the switch 60 times per second (in North America, 120V 60 Hz AC) and less than full current most of the time as it swings from zero to full wave and back down to zero again. This serves to halt an arc across the switch terminals in 1/60th of a second or less, even if you happened to trip the switch when full power was across the terminals. Once the arc is halted, then the distance between the terminals only has to be sufficient to prevent an arc from jumping the switch terminals.

DC is "always on" ... there is never a time when the power is zero in the closed circuit. Some AC-rated switches cannot handle any DC loads without arcing (if the distance between terminals is not sufficient to prevent an arc from jumping the gap).

If you examine the switch body you will rarely find one that is DC rated at all. This is true even with switches found in automotive shops.

Others are built to handle both AC and DC. If that's the case, the switch will be expensive, and will have both ratings marked on the switch body. A switch that is rated for 10A DC would cost at least $20 and usually more. They are also physically large to allow for the gap needed to stop a DC arc.

As a rule of thumb, a switch that is rated for AC only can only be expected to switch 12VDC at 1/20th the AC amperage rating at 120V. So a switch rated 10A 120V AC is only safe for a DC circuit of 1/2 A (500 mA) at 12V DC. As a rule most DC rated switches are rated for 32V DC, but this doesn't mean the rating would be higher for 12V; the criteria for voltage and current limits are different.

With a relay, this won't be an issue ... generally a relay low-current side will have perhaps 100~200 mA across the switch terminals. Just avoid an AC 120V switch rated for about 6A or less. That indicates the switch doesn't have the distance across the switch terminals necessary for 200mA or so; these switches are generally small in size.

If for some reason you need a higher current DC switch, try to look for aircraft surplus switches, eg military surplus. The price for surplus goods would be reasonable enough and they will be rated for DC current (it's illegal not to use a DC rated switch on a DC circuit in aircraft). OEM automotive switches can also be expected to be DC rated, but it's common for OEM parts to not have the ratings marked, since there is no need when used for direct replacement. Therefore you might need to do some research to determine if the switch is adequate for your use.
lopar
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Re: Battery isolator

Post by lopar »

............. so don't pull a switch out of your house and you'll be fine :mrgreen:
almost all ac circuits in an aircraft are controlled with DC, just easier on design and performance and way cheaper when you get into relays and other control components.

started ripping that last post apart by the line...... i'm not that bored........

summarized (approx)
no
said already
no
wrong
said already
wrong, and no
partially true, not entirely
misleading
no
no
wrong (something like that)

Any switch has a "rating" per say, I blade of grass has an electrical rating if you look into it....... the gap, sparking stuff is mostly correct.

An AC rating does not mean anything unless it lists Voltage and Current to gives its "power handling" in addition to "archy/sparky" (voltage), which is basically taking into account the resistance of the switch which will not all calculating the voltage drop that will occur across the switch, which will...... blah blah.

Most switches that come to be in your hot little hands will have 12VDC rating right on it (especially Lordco, Princess auto etc)..... if it has other rating, look it up online and cross the rating to your application, or E=IR DIY :mrgreen:

Don't be afraid of electricity, if you don't know, look online, lots of quick answers if you need them.....

don't forget your fuse!
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Growlerbearnz
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Re: Battery isolator

Post by Growlerbearnz »

Here's my solution to the problem. I'll explain it in the next post as the image is from my phone and typing is hard .
Attachments
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Nothing says "poor workmanship" more than wrinkles in the duct tape.
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Growlerbearnz
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Re: Battery isolator

Post by Growlerbearnz »

The starting battery is connected to these original cables:
-Starter/Glowplugs (black cable, no labels, 2x fusible links coming off it)
-Alternator (black plastic box with "ALT" label, giant fuse out the back)
as well as one large cable that goes to the VSR (I'll explain that in a bit)
And one smaller cable that goes to the coil and normally open contact of a 30 Amp relay.

The accessory battery is connected to the VSR, and to the original accessories cable (black box with LOCK, ACC, errr.. lots of white writing on it. Can't remember exactly what)

The VSR is a Voltage Sensitive Relay, used in marine applications to isolate 2 batteries- when the starting battery is charged/charging it connects the two batteries together, but if the starting battery voltage drains to 12V it separates the batteries.

So, how it works:
Normally the starter battery runs ONLY the starter motor and the glow plugs, the accessory battery runs EVERYTHING else. I can drain the accessory battery as dead a doornail and still have a fresh battery to crank the engine. However, because the accessory battery runs the glow ECU, fuel pump shutoff solenoid, and other things that are kind of important for starting, I've added the 30A relay and a switch on the dashboard to turn it on. Flicking the switch powers up the relay, which connects the accessories to the starting battery.

I have no need to use both batteries in parallell for starting- this setup won't do that. But it was fairly easy to install :-)

Here's the VSR I used: http://www.discount-marine.co.nz/shop/i ... ts_id=1767

Pictures of install here: https://picasaweb.google.com/1171804076 ... directlink
(Ignore the blue diode-type isolator, it didn't work with the Delica's alternator, which needs to see battery voltage on the output wire to start charging)
Nothing says "poor workmanship" more than wrinkles in the duct tape.
RichD
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Re: Battery isolator

Post by RichD »

I covered this in the inverter thread.

You don't need a 300A isolator for a 85-100A alternator. The isolator has nothing to do with starter loads.


A combiner switch is a completely different problem which you can overcome with a separate switch.

The schematics are in the inverter thread.
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