Battery Scenario...Is this feasible?

[inetdog]

That's what I figured. Are we talking about early death syndrome for the Trojans or just an odd use, but no harm.

Thanks, CC

Rich

As long as you do not go too deep into discharge (which engine starting should not do unless you flood the engine and just keep on cranking trying to start) and do not drive the temperature of the battery too high, you should not have any long term bad effect.
You are right though that for a large engine which needs a lot of cranking amps to turn the engine over, you will need to parallel several RE batteries to get the same current capability of a cranking battery of the same size.
I once had a very old Datsun pickup with a 6 volt electrical system, and in the winter the starter pulled so much current that although the engine cranked just fine the terminal voltage of the cold battery dropped so low that the ignition would not drive a spark to actually start the engine. The solution was to let the battery run the ignition and turn over the engine with a hand crank.

[Jim45D]

Depending on what engine/starter, the draw will be in the neighbourhood of 60 Amps +/-. Even one deep cycle will handle this. On an "equivalent" basis, most auto batteries aren't much more than 100 Amp hours. The concern would be V-drop over the wiring distance, even with heavy cables. 2/0 over 6 feet ought to handle it. But I suspect this won't cure the interference problem between the alternator and TriStar.

In my opinion it is best to keep the starting and "house" systems entirely separate, and only connect them if/when necessary with a manual connection.

This happened to me when my mechanic forgot to move the selector switch from house to start. As Coot says, "It depends on the engine/starter." My engine is in the 400 CI range. The house batteries started it just fine, but in the process it wreaked holy havoc with my settings on the Heart Interface Inverter, the instrumentation, etc. The instrumentation is the Link 10. It say's plainly in the manuel to keep the house and starting batteries seperated. I didn't overlook that, my mechanic did. Since that time, I ran completely different wiring to the alternator and starter to JUST the starting battery. The selector switch has since been disconnected. I installed a 10 watt panel solely for the starter battery.

I don't remember the name of the thread, but it was sometime in March, a year ago this past when I started asking questions here on this forum regarding what to do. Coot, and someone else advised me as to what to try....it worked. The entire metering on the MPPT, and the inverter were all amuck, and it stayed as such. It would be best to follow what Coot has already said above.......KEEP starting and House seperate. You'll fare well.

[Wanderman]

Interesting. I have a 200 (really 250-ish) AMP shunt that feeds my battery monitor. I'm going to take a look at the draw with it and a clamp on dc ammeter today. I'll wager the loads is lower than 100 amps...I would have noticed that draw on the big display when i started the engine. I did not see any ill effects on metering at all. My inverter will probably pull more running the microwave than the start does!

Rich

[Blackcherry04]

I have a 4 hp @ 24 V bow thruster that pulls at least 250 amps ( the rating is for 320 amps ) and a set 4 GC'2s and has done so for 15 years with any effect other than the batteries only last 5-6 years. The same batteries have a TR-1524 inverter hooked to them without any issue. If I pull them below 22 Volts it will cut out the inverter with that heavy of a amp draw them. Granted that inverter is only being used as a charger and a power source for a 5000 btu ac. If I had a 100-200 amp shunt connected to them , I guess I would be concerned.

[Wanderman]

Astounding! I just tested the draw from my starter.

According to the BM-2 running through the shunt. With the engine start battery OUT of the loop (disconnected at the terminal) the overall draw maxed at 35 AMPs. Now I had 3 amps coming in from the Solar Panels (raining here) and likely another 3 from the onboard converter charger. The so gross seems to be around 41 AMP. Let's call it 50 total. If I add 1 additional Trojan 27TMX (where am I going to find a used one?) that would mean 50/3 +(net wire loss) = 20 amps per battery (more or less) According to Trojan the 27TMX:


Capacity Minutes Cranking Performance 5 Hr RateAH 20 Hr Rate AH Voltage Terminal
@25 Amps @56 Amps @75 Amps CCA @0°F CCA @32°F
175 - 45 530 650 85 105 12 WNT, LT

So this means it's way UNDER the recommended max draws.

Can't argue with the factory ratings, right.

I really like this solution. It actually simplifies the overall system. I could put a voltage battery disconnect in place of the manual switch on the engine battery...or better still one of the remote ones like a Battery Brain. Just have to figure out which one. It should kick in except in a catastrophe discharge situation. So far I haven't gotten that low at all.

What do you all think?

Rich

[BB.]

Sounds a bit low for starting current (unless this is a fairly small engine). Also, being from New Yawk--You know the cold weather starting issues (cold oil, hard starting).

-Bill

[Wanderman]

BB,
I really don't use the RV in the winter. Coldest I would even THINK about going out would be well above freezing. I LIKE having the water system working! It is stored when it gets cold.

Even if we double the draw, it's still well within the manufacturer specs for a draw. I will change out the engine battery for another 27 TMX (maybe put another one in as well.) Now all I have to do is find 1 or 2 gently used Trojan 27 TMXs that I can put in here. The other ones are fine, but a few years old, so new ones would be a waste.

You know, I LIKE puzzling this stuff out!

Rich