Confused about Fusing Aux Battery??

[teamtexas]

OK heres the scoop.....

I have 2 -100 amp hour batteries for use in the conversion and 1- 100 amp hour battery on the engine. All the batteries are AGM. I want to be able to connect the house batteries to the engine battery so it can be used to assist in starting the engine when needed. I also want to be able to connect the batteries so the house charger can maintain the engine battery while Mona is sitting for a long time without use.

In order to connect the banks together I plan to use this selector switch.
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I plan to install a diode to keep the house bank from pulling any juice from the enigne battery (thanks Mike). Althought I'm not sure of the size . Any one have any ideal?

Now, how do I fuse this? I was thinking I need a 200 amp at the house bank which would protect the batteries if the wire shorts from one bank to the other. But what do I fuse the 100 amp engine battery with and where should the fusing be placed?

If I installed the diode at the engine battery and the 200 amp fuse at the house batteries, would the diode protect the engine battery if the wire between the sets shorts out or goes to ground?

Dan

[Altered Sprinter]

NCV Tin makes no difference independent manual over ride aux microprocessor. covers your two rear batteries plus you mains start battery.
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Aux batteries are direct fused, as photos indicate.
Note the photos shown are spares my mains aux is gold plated to prevent corrosion so far after six years they are still perfect.
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For master battery switch, this switch must be positioned as close as possible to your main start battery,and not placed at the back of the aux batteries.
In doing so when you cut of aux supply there will be no current in the AUX cabling.
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CTEK good for trickle charging can not see the rated amperage,make sure it's good for two batteries if charging both at once from mains shore power.
Richard

[autostaretx]

I plan to install a diode to keep the house bank from pulling any juice from the enigne battery. Althought I'm not sure of the size . Any one have any ideal?
...
If I installed the diode at the engine battery and the 200 amp fuse at the house batteries, would the diode protect the engine battery if the wire between the sets shorts out or goes to ground?

The diode may not be a great idea, since it will "steal" a volt or so (forward voltage drop) when you're trying to charge through it.
That may confuse the charger.

If you're planning on the diode to serve as an "automatic" kick-in for the house batteries to help the starting battery, it would (worst case) need to handle starter current levels. If you're fusing the bank for 200 amps, then a 200 amp diode may suffice.
Prices seem to vary from $20 to $200 (lower voltage drop Schottky are more expensive)
I worry about suppliers such as http://www.bdbatteries.com/diodes.php which say "will safely block up to 85 Amps sustained at 600 Volts", since the 85 amps is the conduction rating, not the blocking rating (when blocking, there's (almost) no current). If they've got "what's happening" backwards like that, it casts a raised eyebrow on their other statements.
Some diode ratings assume usage in a AC-to-DC rectifier application, where they're not carrying current 1/2 of the time.
Running them with high continuous forward current for a number of seconds (such as when starting) would exceed those diodes' ratings.
This "200 amp" diode ( http://www.datasheetcatalog.org/data...QRF0620T30.pdf ) is an example of that.
(the "180° Conduction, Tc=25°C" in the Conditions column is the hint about that)

--dick

[d_bertko]

The Surepower 1315 bi-directional battery separator will combine the banks for charging from either the alternator or shore power charger direction. The smart feature lets the alternator give the starting battery priority.

There is also an optional momentary override switch that allows you to combine both banks for starting.

No problems after 5 years of use. That momentary switch is useful!

I used it after seeing lots of rv converters spec'ing it.

Dan

[georgetg]

Dan,

Contrary to popular belief, the fuses protect the wiring, not the batteries.

Locate the heavy duty fuse as close as possible to the battery.
Look at the positive terminal on the engine battery, there's a good chance the battery bus still has an empty slot for you to tap into...

I'd use a high amp relay to separate the two battery systems.
Tap the D+ signal below the drivers seat (just go fishing for a fuse terminal that is only powered when the engine is running) use that to drive the relay to combine the battery systems.

If you wish add a switch to close the relay even without alternator output...

Your manual switch will do just fine also, but I'd stay away from diodes for high current applications.

YMMV

Cheers
George

Your switch

[Oldfartt]

The use of diodes in this application is inappropriate and in effectual as shown in the data sheets. The diodes are rated at 200Amps for only very short duration, but more importantly is the forward current graph which shows the voltage drop across the diode at between 0.8 Volts at low currents and 2.8 Volts at high currents. At high currents this amounts to large heat generation with ultimate failure.

I note that you have a Ctek charger installed.
Another solution which I am using is a very clever new model from Ctek which does everything you need for charging. See http://www.ctek.com/EN-GB/dcdc/default.aspx
The only function it will not do is to connect the two batteries for starting the engine. For that function a suitably sized manual relay or switch is needed. For the number of times this function is required it is a cost effective option.

Cheers

Ross

[glas1700]

When connecting chassis and house batteries together, I like the KISS method. Buy a Cole-Hersee #24143 battery connect solenoid with silver contacts, rated at 200A continuous, for ~$35. Energize it using the D+ lead and also provide an external switch to be able to use the house batteries to start the engine if needed. Minimal voltage drop, unlike diodes, inexpensive and works very well. Fuse both the chassis and house batteries as close to the batteries as possible with 200-250A fuses.

Byron
07 Navion

[Aqua Puttana]

Originally Posted by glas1700

...
Energize it using the D+ lead and also provide an external switch to be able to use the house batteries to start the engine if needed.
...
Byron
07 Navion

It certainly doesn't need to be complex. I would add that I think the switch to energize the solenoid and connect aux to start battery should be a momentary contact type. That pretty much eliminates the need to worry about whether the system is returned to normal mode or not. The start from aux battery feature should rarely be needed anyway. FWIW. vic

[glas1700]

I forgot to mention that the switch should be momentary, thanks for the reminder. My Navion had a momentary switch in case the chassis battery went south, but since I have a decent solar system with a three stage charge controller, I changed the switch to a on-off-momentary type. Now I can disconnect the D+ lead from the solenoid and rarely use the alternator to charge the coach batteries, preferring to let the solar panel do the work on most days.

The chassis battery, an OEM Varta, is close to five years old and still works perfectly. I attribute that to the solar charge controller that supplies ~2A to keep it fully charged. I'm hoping to match the eight (8) years that I got from the OEM Panasonic battery in my MR2.

Byron
07 Navion

Originally Posted by Aqua Puttana

It certainly doesn't need to be complex. I would add that I think the switch to energize the solenoid and connect aux to start battery should be a momentary contact type. That pretty much eliminates the need to worry about whether the system is returned to normal mode or not. The start from aux battery feature should rarely be needed anyway. FWIW. vic

[Altered Sprinter]

If running the latest MB sprinter with aux optioning for batteries! I'd look a bit deeper on the fusing options...on the separate box of the Mercedes Benz fuse dedicated to aux depending on type and alternator.

Richard

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