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Discussion Starter · #1 ·
While I wait for my big ass alternator to arrive I'm wondering what will be the best way to add a 2nd battery or power source in the back. I'm going to upgrade my sub amp to a 3k amplifier, and plan on eventually upgrading my front end amps to run more power (125x8). This is about 4k but I know I won't be pulling that all the time. I recently put in a D3400 which has been pretty awesome.

I could:

1. Have a supercap bank setup in the back (I'm thinking 500 farad will probably be good enough for the wattage, but if I end up going bigger it makes more sense to get the bigger ones now because a 1000 farad will take up less space than two 500's)

2. Add a lithium in the back. I worry about how it will be affected by cold temps (living in Maine), and it is one of the reasons I avoided lithium when I got the new battery. I'm not sure how I should isolate the two batteries, and how to worry about charging. The lithium also would take up more space than a 500 farad bank, but about the same as a 1000 farad.

Questions lingering:

1. When I install the supercap, from what I've seen they install in parallel with your battery. You charge them to the system voltage using the halogen lamp and then wire them in parallel. Ring terminals from the supercap to your power and ground distribution.

2. Will any of the lithium chargers also charge AGM's or do you need 2 chargers if you have both types?

If you have any good info sources on this stuff let me know, I planned on giving XSpower a ring today to ask them some questions while I continue working on my box build :)
 

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I'm running ~4.1kW (combined Class AB + Class D) on Dual AGM (OEM Starter Battery + XSPower XP750 on the Amp Board) with OEM 240A Alternator and absolutely no dimming on full tilt. Didn't want to deal with the hassle of Lithium and Float Voltages along with Cold weather concerns (we go to the Mountains in the winter and have family in the rust belt) and at this power level (no SPL burps or competition just SQ daily listening) the Supercap is, IMO, overkill. All on 1/0 Welding Cable and 2/0 OEM from Engine Bay Jump Start Post to Starter Battery under the passenger seat (at some point I'm going to replace the 1/0 from Alternator to Engine Bay Post with 2/0 but that's just cause I have it laying around in the shop.)

Now if you were running 4kW of Surfboard Class D or AB Mono Amps then I'd go with the Supercap and AGM but with full bridge Class D I would try it with what you have and then add a small Low Internal Resistance AGM close to the Monoblock if you have any dimming to act as a pseudo Supercap. And yes, supercaps or parallel AGM batteries are connected in parallel. Be very cautious if you do the Supercap and make sure you have the ability, PPE and space necessary to make the connections without any potential change in voltage. 500 Farad = 120kVA (average home only uses a 25kVA Transformer) of available fault current and is a huge arc flash potential if you drop a wrench or something...

They make chargers that can do multiple battery topologies with different float levels but you can't charge them all at one time from a single charger and the idea that the LTO rests at a higher voltage with the AGM constantly draining it during use was something that I wasn't happy trying to balance. Especially with the simplicity of Dual AGM and not needing an isolator (still have one cause I wanted the ability to run them isolated but not necessary.) For reference, I rarely see more than 30A of RMS charging current coming to the XP750 while running full monty.
 

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The Titan 8 lithium works all the way down to -4° don't know how cold it gets I Maine but if ita above that it could be an option.
 

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Discussion Starter · #4 ·
I'm running ~4.1kW (combined Class AB + Class D) on Dual AGM (OEM Starter Battery + XSPower XP750 on the Amp Board) with OEM 240A Alternator and absolutely no dimming on full tilt. Didn't want to deal with the hassle of Lithium and Float Voltages along with Cold weather concerns (we go to the Mountains in the winter and have family in the rust belt) and at this power level (no SPL burps or competition just SQ daily listening) the Supercap is, IMO, overkill. All on 1/0 Welding Cable and 2/0 OEM from Engine Bay Jump Start Post to Starter Battery under the passenger seat (at some point I'm going to replace the 1/0 from Alternator to Engine Bay Post with 2/0 but that's just cause I have it laying around in the shop.)

Now if you were running 4kW of Surfboard Class D or AB Mono Amps then I'd go with the Supercap and AGM but with full bridge Class D I would try it with what you have and then add a small Low Internal Resistance AGM close to the Monoblock if you have any dimming to act as a pseudo Supercap. And yes, supercaps or parallel AGM batteries are connected in parallel. Be very cautious if you do the Supercap and make sure you have the ability, PPE and space necessary to make the connections without any potential change in voltage. 500 Farad = 120kVA (average home only uses a 25kVA Transformer) of available fault current and is a huge arc flash potential if you drop a wrench or something...

They make chargers that can do multiple battery topologies with different float levels but you can't charge them all at one time from a single charger and the idea that the LTO rests at a higher voltage with the AGM constantly draining it during use was something that I wasn't happy trying to balance. Especially with the simplicity of Dual AGM and not needing an isolator (still have one cause I wanted the ability to run them isolated but not necessary.) For reference, I rarely see more than 30A of RMS charging current coming to the XP750 while running full monty.
I mean it is easier to add a supercap in the back (space wise) than adding another AGM. I really like the idea of my AGM up front and the supercap in the back by the monoblock.

I plan on making an acrylic cover for the rear power solution to help protect it some and I've seen the pictures on here of people accidentally shorting them.

The Titan 8 lithium works all the way down to -4° don't know how cold it gets I Maine but if ita above that it could be an option.
We have stretches of -10 and sometimes even colder. I think I'm probably going to be with the AGM for a bit.
 
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I mean it is easier to add a supercap in the back (space wise) than adding another AGM. I really like the idea of my AGM up front and the supercap in the back by the monoblock.

I plan on making an acrylic cover for the rear power solution to help protect it some and I've seen the pictures on here of people accidentally shorting them.



We have stretches of -10 and sometimes even colder. I think I'm probably going to be with the AGM for a bit.
The XSPower XP750 and SB75-680L are the same size. The SB500 is quite a bit bigger than the XP750 AGM... one more reason I went with AGM.

SB500 = 9 x 8.2 x 5.4
XP750 = 7 x 6.6 x 3

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Discussion Starter · #6 ·
The XSPower XP750 and SB75-680L are the same size. The SB500 is quite a bit bigger than the XP750 AGM... one more reason I went with AGM.

SB500 = 9 x 8.2 x 5.4
XP750 = 7 x 6.6 x 3

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Wow, I hadn't realized, that makes it even more of a discussion... The XP750 is pretty tiny.
 

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i'm in similar situation now, myself. i'm really interested in figuring how to choose the appropriate size of supercar bank for given amplifier size/current draw.

i imagine..... because of durability of supercaps, you would want to choose those if they fit/work for your application. they should in theory vastly outlast AGM, right?

@daloudin my memory may be mistaken, but i thought you had 1000F cap bank in your setup?
 

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for my setup, i am building in / architecting in cutoff switches in line with my supercaps/batteries so they can be individually disconnected whenever needed.
 

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i'm just chatting here..... but.... all batteries performance sucks in cold weather, SLA, AGM, lithium. the all have reduced performance especially once getting down to -10F.
Caps would not..... they do not suffer from this issue, so if you're thinking to do it, .... just go super cap route. (i'm a supercap fan, btw) :)
i finally recently ponied up for a a bank, can't wait to test them out.

We have stretches of -10 and sometimes even colder. I think I'm probably going to be with the AGM for a bit.
 

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Yea those xp750's are really small. They even have the cool little braket to hold it. I bought the set from Down4sound with the braket and 4 gauge wire for like 150$ a while ago but I never used it. It's sitting in storage hopefully it's not dead if I ever decide to use it. The wire was CCA though so it went in the trash.
 

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i'm in similar situation now, myself. i'm really interested in figuring how to choose the appropriate size of supercar bank for given amplifier size/current draw.

i imagine..... because of durability of supercaps, you would want to choose those if they fit/work for your application. they should in theory vastly outlast AGM, right?

@daloudin my memory may be mistaken, but i thought you had 1000F cap bank in your setup?
Sizing is all about understanding the ampacity you need. The connected Impedance and capacitance reserves in the power supply of the amplifier all factor into the calculations necessary to determine what you need. The recommendations from manufacturers like XSPower are usually higher than you actually need to make sure that they don't get complaints from bassheads who used those recommendations to size theirs and then still have dimming. Having more than you need is never a bad thing as long as you have the rest of the electrical to support charging that connection. XSPower says you need 500F for 4kW but 500F can discharge around 10,000 Amps at 12VDC so that's 120kVA whereas (without getting into the weeds about how many microseconds that discharge can happen in) and kVA at a Power Factor of 1 is a direct conversion to kW so that's technically 120kW of power that it is capable of providing... but it all comes back to the Alternator and connected ampacity of all the peripherals as well, so how much is coming from the Alternator (at what RPM and if you listen Engine Off or Running), Battery and Capacitor together along with resistance of the wires, connections and terminals all play into determining the ultimate need. But you can't measure all that (unless you have access to really nice measurement equipment) so we connect things up and see what kind of voltage drop we get and go from there - not really what you wanted to hear but it is what it is...

No supercap in mine. Did a parallel install when I was doing mine with 2 x SQL15D2 at 0.5 Ohm Sealed on SALT 6K with a 1000F Supercap from XSPower and a 440A (2 x 220) Alternator but that wasn't mine. He had dual SLA batteries from the factory in his Pickup but eventually swapped them out for D3400's as well.

As for the longevity it all has to do with how you use, abuse and maintain the system. The electrolytic in a capacitor theoretically should last indefinitely but with heat cycling, power surges and the automotive environ in general they do break down over time just like the electrolytics in the amplifiers. The same goes for an AGM or SLA battery, if you never drain the battery below 85% then they could also have an indefinite life cycle. The OEM AGM Starter battery in my 2012 Grand Cherokee lasted 10 years and 155,000 Miles and I'm still using it for a trolling motor in a Jon Boat. The fact that the batteries in my Jeep are in the passenger compartment versus the heat (and cold) of the engine bay certainly aids in their life cycle.

Electrolytics are much better at the instantaneous needs of an amplifier for impulse current but then you also have to have the wiring from the Alternator to support that same current flow to keep it charged. It's a vicious cycle and only the pocketbook and listening style of the owner can predicate which method you use. Mine is mostly less than 100-105dBC average listening level so I really don't need the huge ampacity of the Supercap and the XP750 is plenty for me.
 

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I mean it is easier to add a supercap in the back (space wise) than adding another AGM. I really like the idea of my AGM up front and the supercap in the back by the monoblock.

I plan on making an acrylic cover for the rear power solution to help protect it some and I've seen the pictures on here of people accidentally shorting them.



We have stretches of -10 and sometimes even colder. I think I'm probably going to be with the AGM for a bit.
you can easliy run the super cap bank in the rear. I ran a 500farad maxwell along with a 36ah lishen lithium lto bank and even kept the front agm battery hooked up. There was absolutely zero issues. I had a 370amp alternator also. My voltage barely moved even with 3000 watts.

there is a great lithium Facebook group to get good info. You won’t get proper info and answers here since this is mostly SQ guys that have not researched or know about lithium simply because they have no need for it.
 

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Nice man, thanks. Below is describing 1 time pulse, I think? In reality with music a system may draw (just making this up for a random 2000W system with music) 200A for 10 milli-second pulses, 1 time per second for 3 minutes. also you are charging the supercap between discharges, it's a pretty dynamic situation.

XSPower says you need 500F for 4kW but 500F can discharge around 10,000 Amps at 12VDC so that's 120kVA whereas (without getting into the weeds about how many microseconds that discharge can happen in) and kVA at a Power Factor of 1 is a direct conversion to kW so that's technically 120kW of power that it is capable of providing
i think it is this and also the current draw over time as well.

Sizing is all about understanding the ampacity you need.
for sure on this one, that's super nice.

The fact that the batteries in my Jeep are in the passenger compartment versus the heat (and cold) of the engine bay certainly aids in their life cycle.
and you are correct, i do not like this, lol. :geek: should able to test/calculate something here. i mean you are totally right. do you follow XS power recommendations typically?

so we connect things up and see what kind of voltage drop we get and go from there - not really what you wanted to hear but it is what it is...
 

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I still say you snatch up an AGM for the front and a titan8 lithium for your trunk and insulate the rear battery to keep it warm. Even if it went down to below -4° where that battery is rated for your probly not going to damage it. Probly see a reduction in performance at those times but it's not going to spontaneously combust.
 

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I still say you snatch up an AGM for the front and a titan8 lithium for your trunk and insulate the rear battery to keep it warm. Even if it went down to below -4° where that battery is rated for your probly not going to damage it. Probly see a reduction in performance at those times but it's not going to spontaneously combust.
Titan it way overpriced and has little power this why I say don’t ask about lithium in this forum.
Titan 8 10ah is 700$. It’s just lithium lto. It’s not magic. Lishen lithium lto you can get close to 64ah of lithium power for that price
 

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I wouldn't call it little power. I'm running around 6k with a RSV-5 and a PWR-5 with hardly any voltage drop on a stock 130 amp alternator. The RSV-5 alone handled 4k on its own and didn't do bad on 6k. My voltage would drop to mid/low 13s at idle with just the RSV-5. I don't feel 700$ is expensive, look at how expensive everything else we run in our sound systems is. I will eventually upgrade the alt when the warranty expires but at this point its not even necessary.
 

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I guess we all have a different definition of expensive. No internal pics at least I haven't seen any. I did research TF out of lithiums before settling with the Titan8s. And that's what worked best for me. Don't take up space, super light, handle the load I throw at it, I wasn't about to build my own. And all the built in bussbars are nice even though I didn't use em.

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