Fusing the Yandina on an Aux Battery

[iiigoiii]

just curious if most people here using the yandina combiner are putting fuses on the leads on either side.

the instructions say that it's not strictly necessary, as there are no significant internal paths to ground were it to fail, but of course the leads themselves could short to ground.

i was just looking at the yandina's amp ratings - it can go up over 100a for short periods, and presumably that could happen if you started the van while the yandina was in 'combined' mode. also interesting is the info on the yandina site that the combiner amps are limited the greatest for closing current - if already closed it can carry larger amps; it however only has 10ga leads i believe.

if fuses were used on the leads, the fuse would have to be a very large one if the intention was to use it also in 'combined' mode for starting.

(tencentlife - i noticed that you have an 80a fusible link between your aux battery and everything including the yandina - wouldn't this blow if you used it to jumpstart the van?)

thanks....

[tencentlife]

I think it would be pretty wise to put a fuse at both battery + poles where the Yandina leads connect, but then again there is no fusing on the main starter lead from the primary battery, so what are you gonna do? Vehicle wiring as built by the manufacturers leaves a lot of basic electrical safety unaddressed. If you were going for full protection there would be a 400A Class T fuse right there on the main battery +.

So anyway, bearing that in mind, and knowing that my routing of the Yandina wire is pretty safe (unless someone starts mercilessly hacking apart my aisle carpet with a razor knife, but anyone who does that to my friggin' van is about to have a lot worse than electrical fire to worry about), I only put a main fuse on my aux battery to protect the inverter. That's the 80A; enough for the inverter's steady-state output.

If combining the batts for emergency starting, I don't see that the aim is to use both in direct parallel. The Yandina could only theoretically carry 100A anyway, which would be about half the starter load if it could, but I bet it can't really sustain that kind of draw anyway; 10ga. wire is safe up to 30A and would carry much more briefly but I wouldn't want it to.

The way I see using the combiner to aid my main battery, should the need arise, is just to combine it and let the charges equalise for a minute; that may elevate the main voltage enough to use the starter, and would lessen the draw off the aux. If the main is really bad I would parallel with jumper cables instead.
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[iiigoiii]

interesting, i just read some more on the subject of starting from the yandina FAQ:

[tencentlife]

From a safety perspective, the primary purpose of fusing is to protect against dead shorts, since dead shorts cause fires. The secondary purpose is to protect wiring and equipment from simple overcurrent, for instance when the fan motor is getting tired and runs but uses more amps than it should. Overcurrent due to degradation in a case like that generally heats the wire and damages insulation and connections, but the rate of heating is gradual enough that heat dissipates so you don't get actual ignition.

In a dead short the heating is instantaneous and can blow off the insulation so fast it actually catches fire, or adjacent materials ignite because the insulation no longer shields them from the overheated wire. So the reasons for fusing differ. A regular fuse protects against overcurrent by capping it definitively at a certain point. A slow-blow allows more current to run in a circuit momentarily, but if it rises too fast and exceeds a certain limit, usually much higher than the fuse rating, it will open quickly. This is what you would see with a dead short.

When the aim is to protect a large battery-driven circuit from dead short it's the Amperage Interruption Capacity (AIC) of the fuse that matters most, because when current rises very high very fast it can overwhelm conventional fuses; essentially they burn open but the high current can arc right across the open circuit, making even more heat.

A lead-acid battery can dump unbelievable amounts of current into a dead short instantaneously. If you've ever shorted the positive on your car battery you have seen this in action, watching a steel wrench melt instantly. That's why to protect battery-based systems with high-current wiring like solar installations we always specify a Class T, which has an AIC of 20kA or higher. These are available from solar equipment dealers for about $20 apiece in various capacities. They have flat drilled tabs that usually are bolted to a special fuse holder, but also allow one to be bolted directly to a battery positive post (on industrial batteries; car types with round posts would need some adaptor), and the wire can be bolted to the other side. That protects every inch of wire from dead short with the high AIC you want. Then you use conventional fusing to protect smaller loads fed by that battery. We call the Class T the "Hail Mary" fuse.

Nice to know the Yandina can handle surges at higher current if needed, but I'm still wary of making a 10ga. wire handle that much current. But since the whole purpose of having an auxiliary battery is to preserve the charge level of the main battery for starting, the question of how to boost the main with the aux is kind of academic anyway. It's the aux that will have a low voltage in most cases, since you're using that for accessories while leaving the main alone. But it is good to know how to handle the situation should the main suddenly die on you.
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[climberjohn]

Tencent,

The class T fuses you are talking about that can be bolted directly to the positive battery terminal . . . do they look like this?

http://store.solar-electric.com/f150ampcltfu.html
F-150T 150 Amp Class T Inverter Fuse

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[tencentlife]

Yes.
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[singler3360]

[tencentlife]

Yes.
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[climberjohn]

Tencent,

Thanks for the clarification. (And for setting a record for your shortest post ever)

Singler, thanks for the hug. I learned a long time ago that asking apparently obvious questions here usually leads to kind treatment. Adding a link and a photo can further clear the murk.

My whole aux battery setup is rather a mishmash, some rigged more or less correctly and some wired pretty half-ass. I'm reading some "back issues" of aux battery setups to try and get some improvement ideas (correct wire gauges and fuses in the right place), and doing this is part of the remodel.

-CJ
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Know your limits. Exceed them often.

[singler3360]

[iiigoiii]

you can also find class t fuses at amazon, including a 200A slow-blow for $24 shipped. search the automotive section for 'go power class t fuse'. (note- to get the free shipping you have to click on 'amazon' under the 'sellers' box on the left hand side, or else they'll list some with high shipping charges from other vendors.)
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[outwesty]

Almost finished my new aux install. I have not yet fused the three 6awg leads coming off of my battery (all less than 17 inch runs). One is for a Xantrex Prowatt 600 (80a fuse recommended), the new fuse panel and the IOTA 15 amp charger. I have a 4th wire going to the Yandina on the + side as well.

I just found these Blue Seas post mounted fuses available from 30 to 300 amps. Just thought I would share. Seems much easier than cutting the leads and installing fuses in line off the batt. I am going to run the single version with an 80a. I suppose if the Yandina blows it I can get a two gang version and up the amperage on that side. These are not class T. Think this will be okay ?

not mine. just to show the fuse design.

[Gnarlodious]

The Yandina is equipped with long 10 gauge leads that limit current in case of a meltdown. If you cut these leads the unit is not warranteed, due to the increased current short leads would pass. I think they are only worried about the contacts burning out, because hot #10 cable can still cause damage, if not outright flame.

I cut the leads off and installed the Yandina in the side panels where they could only contact metal if they burned. Since my intertie cable is #8, I figure the #10 will burn first. That’s my big fusing system.
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