2 batteries in a prius

Sorry - I just read your 2011 February 17 at 7:50 PM reply (5th up from here). As I wrote, IMO batteries should not be paralleled unless being charged. IMO they can be paralleled when in use (being reasonably loaded), but that too has a "matching" argument (same history, batch, discharge). Otherwise if left paralleled for long periods, IMO they should be matched with equal impedance interconnections and "diagonal" outlets (+12 & GND). [That's for 2 batteries; to achieve "symmetry" for 3 or more batteries, the interconnection and outlets get more complex.] The above IMOs are for maximum battery life and to avoid AGM thermal runaways or acid-boiling etc. Others have their opinions. (I mentioned the example of the audio forums that are recommending replacement of batteries 4x to 8x as often rather than increasing battery size by (say) 20% and having a normal life? Their opinion is definitely good for battery manufacturers and the economy. And who give a doodiee about more depleted uranium and other battery chemicals in our environment anyhow? IMO it's a similar outcome by NOT isolating idling batteries.)

the cheapest isolator i found is $40. my friend recommended noco but they are like $80-90 for 200amp. so you think sunforce 150 amp isolator is a bad one? what about noco 200amp? http://www.adventurerv.net/high-performance-battery-isolator-200-amp-p-4006.html

also, u said i could tap into the ign for my 12v switched to the isolator. couldnt i just u the remote wire coming from my stereo, and tap into that to connect to the isolator? so i would have the remote wire from my stereo going to my amp. then tap into it an run that wire to the isolator. sounds right to me, what do u think? if i can find a 200amp for $20 that would b great but i need the isolator like yesterday. so i dont mind spending the $80 or what not. let me know what u think. thanks

It's quiet. Too quiet.... The quote in my last reply is from my 2nd reply which is the 4th reply in this thread. I quoted that because IMO I have answered all you are asking, or given my opinion to yours and others suggestions. I realise this may not be clear. I reply with a lot of info at once. It often takes several reads before it makes sense. Sometimes it never makes sense - often because my expression is poor, ambiguous, unsuitable. If you have specific questions or need clarification, ask. I can't put it much simpler than the following: - You do not need a "smart isolator" - a plain relay will do (appropriately rated). - If you do not draw more than about 50A (ie, the sustainable converter current), you should not need added battery capacity. Furthermore: - You may chose to change or increase your main battery anyhow. - If you draw more than 50A (the converter capability), you will need larger or extra battery(s) that provides suitable reserve time (ie, prevent a flat battery). - The 50A includes headlights and other Prius control functions. - Your added load reduces the main battery range, but the petrol motor starts and generates replacement charge.    - You should add a manual switch else low-voltage cutout to enable isolation of your extra battery(s) should the load be too high (ie, you want to prevent the Prius 12V system battery from flattening). - I highly recommend an in-dash or suitable voltmeter to monitor the extra and system battery. (This should be the norm for ANY vehicle! Especially those with big loads.) - Smart Isolators (voltage sensing) may not suit this application (as with many) - their voltage hysteresis and time delays may be inappropriate. - Forget diode isolators. Good for small power (a few Amps); but IMHO stupid and expensive for vehicle power systems. - When not in use, batteries should not be paralleled (IMO). - If permanently paralleled, batteries should be a exact match (batch, history, environment, temperature) with symmetrical charge and drain - but even so, their unreliability doubles (2 batteries; trebles for 3 etc).

hey sorry i just got home, i was out of town on business for a few days.just wanted to let u know real quick i will read all your posts tomorrow. i still havent ordered a isolator yet, was lookign into a few. i hook up the amp and sub with a inline 250a circuit breaker. and every 5-10 mins it would trip. every single light in the car flickered and that was with the amp turned almost all the way down and the car volume about half way. the second battery is here so tomoro im going to figure out where its going and order a isolator. im exhausted so i will write back tomoro.

100A should be enough for the amp based on its Manual; certainly 250A more than enough. (IMO 100A may be a bit low if it outputs 1kW@11V input - that should mean more like 110A (maybe 120A), though a 100A fuse will handle 110A for hours if not permanently, and 120A for several to tens of minutes upwards. Even if you have paralleled the JL 13W7 coils, 250A should handle it. It might be that surges effect the circuit breaker, or heat. But without another battery or the Big 3, the flickering doesn't surprise me. The converter only handles a max of 50A so the rest comes from the battery. And if that battery is small, and distant, and with standard ground cables... The isolator needs to handle the amp draw plus the battery recharge current. EG - over 100A plus up to 100A = (say) a 200A relay - though if the 250A breaker keeps tripping, find out why! Maybe omit the isolator and just have the breaker (at each end) for now, and manually isolate when NOT in use. If stable, get a relay with rating equal or greater than the breaker/fuse size. A ~200A relay should only cost ~$20-$25.

its hooked up in series at 3ohms. the jl amp runs the same from 1.5-4ohms. so didnt see much of a reason to rewire it parallel. i had a 300a before but i broke it so im borrowing this 250a from my friend. until my 3 new 300a get here. i originally had a 150a in my old car and it always tripped so i just got the 300a. i thought the 150a would have been enough for my old setup too. but i wasnt going to keep buying circuit breakers until i found one so i went right to the 300a. i have the 1400w battery in (switched it with my original battery) and i was so beat today that i slept all day and didnt get anythign done. so tomoro i will be finding a place for the 1800w battery. i was going to do the big 3 but when i went to do it i realized i didnt have a alternator. and from what i know u do the same thing on each terminal so i wasnt going to upgrade the ground wire if i was keeping the original wire to the car(off the pos terminal). i knew the car ligths woudl flicker but was suprised on how much (look like strobe lights,lol) im just guna get the pac200 isolator... i cant find one cheaper then it. its what i had before and worked fine. i have looked and looked an have not been able to find a relay for $20 or even $30.

As long as the paths between the battery(s) and the amp handle the current - including ground - that is the intention of the Big 3. You do have an alternator (in effect) - it's the DC-DC converter. (I'm ignoring the regenerative motor because the 12V does not see that.)

well with the isolator i could just leave the wiring to the main battery as it would only be factory stuff connected to it. that converter box in the front is the thing your speaking of as being the alternator. i cant find a wiring schematic and dont want to mess with it to find the 12v wire. there is a few factory wires attached to a bracket that is attached to the battery. i would do the big three but as i stated i have no schematic and dont want to mess with 240v as i value my life some what. also i value my car and all the things in it. therefor i would have no idea ow to safely do the big 3 in the prius. i might be over thinking and not sure as exactly what im doing....i would feel more comfortable having someone do it that knows what they r doing but i even asked the ppl at the dealer how i would do the big three and they told me to take it to a car audio shop, i asked my friend what his shop would do and he said no one knows anythign about the prius. i went to a shop near me and they couldnt believe i have a w7 in a prius. if i could get some clear directions (instructions) on how to do the big three in the prius i might give it a try. im running 0 gauge from main battery to aux battery ( im sry i mean from the isolator to the batteries) 0 gauge for grounds. 4 gauge to amp(as thats all the amp takes) or if i can find some adapter ends i will run the 0g to the amp. but the car audio shop is outrageously priced for the 0g-4g adapter ends. and of course everythign gets soldered. im heading out in a few minutes to start planning on where to put the second battery. i have room on my amp rack for the isolator. i will keep u posted as to whats happening. you said that pac200 was ok right? if u know of a way to do big three let me know. but if that battery is isolated and only runs factory components i dont see the point. oh i remembered that i grounded my amp to the battery ground so maybe thats why it was trippin the circuit breaker. i just did it quick to hear it and see what it did. i will be grounding to frame as soon as everythign is in place.