Batterie relatively useless on space stations?

[Sky Captain]

Hi, I've been playing for a while and understand most of the game, but something that baffles me is batteries. I used to have a problem with my command pod running out of juice while on the Dark Side of the Moon. I (naively) thought that attaching batteries to my orbiter would allow the command pod to draw charge from them and continue running, therefore allowing it run while out of range of the sun. But for some reason, it doesn't. Why?

TL;DR Want batteries to power command pod, the don't. Bug or feature?

[sojourner]

Works for me. Of course you realize that batteries don't recharge themselves? You need solar panels or the RTG on your ship.

[Enigma179]

Batteries are essentially extra electric charge storage, so that you can last longer in situations when you don't have power (or don't have sufficient power) being supplied. For example, when you've got solar panels your command pod is being charged up but once the body you're orbiting (or even the one you're not, as a kerbin eclipse once taught my mun orbiter) obscures the sun, you're running off whatever you've got stored until it's in view.

For short-term craft (such as extensions to a space station which already has solar panels or generators) I can just strap on a battery instead of a few solar panels or generators, but for anything long term you can't just live with the batteries; they extend your life, they don't make it infinite like a generator or panel will.

[RocketPilot573]

All batteries (Pods have built in ones) are drained simultaneously. So adding batteries just makes your Pods lose power much more slowly, so batteries do indeed work.

[Frederf]

Electric charge is drained in an equalized manner with respect to the max capacity (or is it current value?) so if you had batteries of 900, 50, and 10 max capacity that started full they'd all be at 81% full, 50% full, 12% full, etc. simultaneously. Depleted batteries simply don't drain but don't impact the fact that charge is available.

What you've found is that with craft that have charge generation is that all batteries need to be is a buffer. The buffer only needs to span the maximum length of no power gain times the power consumption, assuming the buffer is allowed to fill completely after being needed. The longest times you're likely to encounter are surfaces of slow rotating bodies say a Ke miner on the backside of the Mun.

[Skorpychan]

Batteries don't power anything, they just store power. Want power in the dark? Add an RTG or two.

I suggest designing a power plant module for the station. A few Rockomax-size batteries, some Gigantor panels, and RTGs. That should be enough to charge anything up quickly, and power everything.

[capi3101]

Batteries don't power anything, they just store power. Want power in the dark? Add an RTG or two.

I suggest designing a power plant module for the station. A few Rockomax-size batteries, some Gigantor panels, and RTGs. That should be enough to charge anything up quickly, and power everything.

I would think either Gigantors or RTGs would suffice, not necessarily both. My personal preference is RTGs of course (because they aren't reliant on Kerbol to supply power) but everyone will tell you they have a pretty lousy mass-to-power production ratio. In my experience, a large battery bank will suffice to get you through the night and the Gigantors charge them up rapidly upon sunrise. I also use a trio of Gigantors; that way at least two panels face the sun even if the third is blocked due to the craft's orientation. If you take a sufficient number of RTGs, you shouldn't need batteries at all...only time I've had issues with them is when I've had to power up an ion thruster.

[DChurchill]

I would think either Gigantors or RTGs would suffice, not necessarily both. My personal preference is RTGs of course (because they aren't reliant on Kerbol to supply power) but everyone will tell you they have a pretty lousy mass-to-power production ratio. In my experience, a large battery bank will suffice to get you through the night and the Gigantors charge them up rapidly upon sunrise. I also use a trio of Gigantors; that way at least two panels face the sun even if the third is blocked due to the craft's orientation. If you take a sufficient number of RTGs, you shouldn't need batteries at all...only time I've had issues with them is when I've had to power up an ion thruster.

My current station has a ton of the 1K roundy battery packs. I think at this moment is has something over 10K of battery storage, 4 RTGS and 8 Gigantors. Overkill at it finest in the spirit of KSP. It obviously doesn't need all that, the RTGs are probably plenty, but it looks cool.

I just have RCS for minor orbit changes, no ions.

I think that power generation and storage needs an overhaul to be honest. And some different RTGs would be nice, too.

[capi3101]

I think that power generation and storage needs an overhaul to be honest.

No argument there...

And some different RTGs would be nice, too.

Well, they actually do look like that in RL; central cask and cooling vanes.

[allmappedout]

Hi, I've been playing for a while and understand most of the game, but something that baffles me is batteries. I used to have a problem with my command pod running out of juice while on the Dark Side of the Moon. I (naively) thought that attaching batteries to my orbiter would allow the command pod to draw charge from them and continue running, therefore allowing it run while out of range of the sun. But for some reason, it doesn't. Why?

TL;DR Want batteries to power command pod, the don't. Bug or feature?

I think there's a disconnect between expectation and reality here. In reality our 'batteries' that we put into a TV remote or a toy last for days, weeks, months even, however within the confines of this game, and the far higher charges used to spin up a reaction wheel or power an ion engine (for example), a battery will drain much quicker than you would naively expect.

They definitely work as expected, but they require a recharging source, typically solar panels, RTGs or large engines with alternators.

Edited August 5, 2013 by allmappedout

[Skorpychan]

I would think either Gigantors or RTGs would suffice, not necessarily both. My personal preference is RTGs of course (because they aren't reliant on Kerbol to supply power) but everyone will tell you they have a pretty lousy mass-to-power production ratio. In my experience, a large battery bank will suffice to get you through the night and the Gigantors charge them up rapidly upon sunrise. I also use a trio of Gigantors; that way at least two panels face the sun even if the third is blocked due to the craft's orientation. If you take a sufficient number of RTGs, you shouldn't need batteries at all...only time I've had issues with them is when I've had to power up an ion thruster.

Anything worth doing is worth overdoing, I say.

[RexKramer]

Hi, I've been playing for a while and understand most of the game, but something that baffles me is batteries. I used to have a problem with my command pod running out of juice while on the Dark Side of the Moon. I (naively) thought that attaching batteries to my orbiter would allow the command pod to draw charge from them and continue running, therefore allowing it run while out of range of the sun. But for some reason, it doesn't. Why?

TL;DR Want batteries to power command pod, the don't. Bug or feature?

Other posters have mentioned you need a power source to recharge your batteries- otherwise they will run out eventually, no matter how many you have.

Adding solar panels to your ship will recharge your batteries, while the sun is shining on them. Usually, your batteries have enough stored energy to power your ship while its behind a planet or moon during orbit.

One important step is you have to deploy your solar panels (in most cases..). I have forgotten to deploy solar panels, the result is an unpowered ship, which can no longer deploy the panels to recharge batteries.

You may also want to watch your electric status as you orbit. It's normal for your batteries to go down while the sun is blocked, but you should verify that the battery status goes back up while the sun is hitting it. If not, check to make sure your solar panels are deployed and working.

[Geschosskopf]

Batteries are useful for 1 thing and 1 thing only. That 1 thing is to provide a source of extra electricity during occasional, short-duration periods of high electrical consumption that exceed the output of your RTGs and/or solar panels. The idea is, your RTGs and solar panels can handle normal needs and keep the vehicle "alive", and also keep the batteries charged. But sometimes you suddenly need a lot of electricity, so you get it from the batteries.

It's really hard to imagine when such a scenario would ever happen. Electrical consumption tends to be a long-term thing. Either you've got the constant, low-level usage (keeping the brain alive, the lights on, and the reaction wheels turning), for which 1 or 2 RTGs suffices, or you've got long-term, high-level usage (driving a rover long-distance, drilling/refining Kethane, etc.), for which you need lots of RTGs, huge solar panels, or mod generator parts. Batteries don't help with either of these because they discharge too fast.

So to answer the OP's question, I find batteries totally useless for all normal vehicles. They add weight without giving any benefit. The only thing I'd put a battery on would be something with a very short lifespan, like a missile, an escape pod, or some such. Just enough electricity to get on its ballistic course, after which it doesn't matter if the brain dies.

[Tiron]

Batteries are useful for 1 thing and 1 thing only. That 1 thing is to provide a source of extra electricity during occasional, short-duration periods of high electrical consumption that exceed the output of your RTGs and/or solar panels. The idea is, your RTGs and solar panels can handle normal needs and keep the vehicle "alive", and also keep the batteries charged. But sometimes you suddenly need a lot of electricity, so you get it from the batteries.

It's really hard to imagine when such a scenario would ever happen. Electrical consumption tends to be a long-term thing. Either you've got the constant, low-level usage (keeping the brain alive, the lights on, and the reaction wheels turning), for which 1 or 2 RTGs suffices, or you've got long-term, high-level usage (driving a rover long-distance, drilling/refining Kethane, etc.), for which you need lots of RTGs, huge solar panels, or mod generator parts. Batteries don't help with either of these because they discharge too fast.

So to answer the OP's question, I find batteries totally useless for all normal vehicles. They add weight without giving any benefit. The only thing I'd put a battery on would be something with a very short lifespan, like a missile, an escape pod, or some such. Just enough electricity to get on its ballistic course, after which it doesn't matter if the brain dies.

They're also good for those times you're eclipsed by whatever you're orbiting and still using power.

But keep in mind, there's been a MAJOR change in power consumption just in 0.21: Turning the ship via reaction wheels now uses electricity, even if it's just the ones built into a pod. It's a pretty serious load, too. I used a cupola's reaction wheels to drain its batteries as part of a test earlier, and while turning on all three axes at once it was draining 2.8 electricity per second, I think it was.

This is going to make both storage and power supply more important.

And last I checked, it does NOT drain power storage relative to capacity, but takes an equal amount from all available storage at once. Meaning the small ones will run out while the big ones are still at a significant portion of their capacity.

Part of the reason it may have caught OP off guard is that most engines generate power while they're running, so he may not have realized that by default there's not actually a built-in power generation device on the ship as a result.

[DChurchill]

Well, they actually do look like that in RL; central cask and cooling vanes.

By cracky they do. Huh. Never actually looked it up. Sort of changes my opinion a little. Still, more options would be good.

[Skorpychan]

I tend to use batteries as the main source of power for my rovers, rather than relying on regeneration matching output. I use small rovers with six wheels, so there's not much room for an RTG or panels. A couple of batteries on the back make it run for a good while before needing to stop and recharge.

I can deploy panels on it for longer drives or charging the batteries faster, but they're fragile things.

[DChurchill]

With 4 RTGs, lights on at full acceleration, it just barely hits the batteries and will eventually run them dry. It probably doesn't need that much storage. Maybe putting one of those new 200 unit small roundy ones where the octagonal strut is might save considerable weight. It's a little top-heavy. I have a tendency to over battery my craft. Even more so now with the reaction wheels drawing so much power.

[GDJ]

My current station has a ton of the 1K roundy battery packs. I think at this moment is has something over 10K of battery storage, 4 RTGS and 8 Gigantors. Overkill at it finest in the spirit of KSP. It obviously doesn't need all that, the RTGs are probably plenty, but it looks cool.

I just have RCS for minor orbit changes, no ions.

I think that power generation and storage needs an overhaul to be honest. And some different RTGs would be nice, too.

Nice! So far my station has 180K of battery storage (I have alot of hydroponics, water purifiers, etc. on board) and at least 10K of solar panels. Basically I can go behind Kerbal and only lose 30%.

The battery packs charge up within a couple of minutes. Electricity is everything, especially in the cold dark of outer space.

Come to think about it, there are mods out there for bigger RTG's. Forgot the name unfortunately, but it's all in the spaceport add-ons.

[M4ck]

DSM pack has a really heavy and powerful reactor I like to put as a part of my base/Kethane refinery, the pod also has a small generator built in, but if I remember correctly, no built-in reaction wheels yet. All the parts are quite heavy, but look good in orbital/landed stations.

[Tiron]

With 4 RTGs, lights on at full acceleration, it just barely hits the batteries and will eventually run them dry. It probably doesn't need that much storage. Maybe putting one of those new 200 unit small roundy ones where the octagonal strut is might save considerable weight. It's a little top-heavy. I have a tendency to over battery my craft. Even more so now with the reaction wheels drawing so much power.

Yeah, the 200 unit ones weigh half of what the 400 unit ones do, so with one of those on top you'd have 1/4th the battery weight you do now. I'd probably slip an OX-STAT or two on it just to give it SOME recharging ability, but they're really light, especially compared to batteries. They also won't break off if you move with them deployed, so they're really the only solar panel type that's viable on a rover.

[Geschosskopf]

But keep in mind, there's been a MAJOR change in power consumption just in 0.21: Turning the ship via reaction wheels now uses electricity, even if it's just the ones built into a pod. It's a pretty serious load, too. I used a cupola's reaction wheels to drain its batteries as part of a test earlier, and while turning on all three axes at once it was draining 2.8 electricity per second, I think it was.

This is going to make both storage and power supply more important.

I must respectfully disagree. Even in 0.21, I see no use at all for batteries. 2 RTGs is more than sufficient to run the reaction wheels of any command module or probe core plus an extra SAS unit, plus lots of lights both big and small. This is all you need for any 1 lander, probe, orbital ship, airplane, SSTO, or station module. In fact, you can probably get by with 1 RTG but I like having 2 for weight symmetry.

So that's your daily, household consumption. No need for solar panels, no need for batteries when the sun goes down. You only ever need more power if add something that really sucks electricity, such as a Kethane drill or processor, an ion engine, etc. But these things typically only run for several hours at a time, so you don't need to build that much power in for constant availability. This is when you use 4-8 Gigantor solar panels, to use just to power these items and to fold up when not doing these tasks. Because the solar panels provide enough juice themselves, you don't need the extra weight of any batteries.

[Tripzter]

Toss a nuclear charger or two on your station just to keep the light on when the sun goes down if you dont have enough batteries to last the few hours the sun is blocked. Hope eventually they will make the solar panels useful but so far our lights is our main drain on our electricity.

[robot256]

I don't use RTGs very much because the same mass of solar panels and batteries still keeps lights on and produces much more total power. I also have ships that use a lot more electricity than usual because of various mods (RemoteTech, Kethane, Mapsat, KAS).

[Tiron]

I must respectfully disagree. Even in 0.21, I see no use at all for batteries. 2 RTGs is more than sufficient to run the reaction wheels of any command module or probe core plus an extra SAS unit, plus lots of lights both big and small. This is all you need for any 1 lander, probe, orbital ship, airplane, SSTO, or station module. In fact, you can probably get by with 1 RTG but I like having 2 for weight symmetry.

So that's your daily, household consumption. No need for solar panels, no need for batteries when the sun goes down. You only ever need more power if add something that really sucks electricity, such as a Kethane drill or processor, an ion engine, etc. But these things typically only run for several hours at a time, so you don't need to build that much power in for constant availability. This is when you use 4-8 Gigantor solar panels, to use just to power these items and to fold up when not doing these tasks. Because the solar panels provide enough juice themselves, you don't need the extra weight of any batteries.

2 RTGs only provide 1.5 electricty per second, or 90 per minute. Reaction Wheels require 18/minute PER AXIS being rotated on. Command pods vary with the amount of torque they provide. The worst case is the mk1-2 command pod, which uses 1.2 per second PER AXIS. A mk2 lander can uses 45/minute (the full output of an RTG) per axis, the mk1 command pod is only 14.4 per second per axis. Cupola is 54/min/axis. Mk 1 lander can is 18/min/axis. You can see it varies a lot, but a small number of RTGs is only going to be sufficient in all cases if you're either only rotating on one axis at a time, or sticking to small command pods and probes.

A single, deployable solar panel array provides 2/sec if locked onto the sun properly. Two of them (the minimum realistic amount) would provide 4/sec, and weigh only 0.035 T. A single RTG weighs 0.08 T, and produces less than a fifth of the power of two arrays. Batteries weigh 0.005 per 100 charge stored. This means, potentially, for the weight of a single RTG you can get two solar panel arrays and enough batteries to store up to an additional 900 charge. More likely is storing 800 via a pair of Z-400s. So for less than the weight of 1 RTG (0.75 power per second) you can get 2 solar arrays (4 power per second), and two large radial batteries (800 power storage).

If you go by power production, to match two solar arrays you'd need 5 1/3 RTGs, but let's just go with 5. That would provide 3.75 power per second. It would also weigh 0.4 tons, which would mean that with two solar arrays you can now fit up to 7300 power worth of batteries while still matching the weight. You're probably not going to fit anywhere near that much, so it's most likely a net weight savings almost regardless of what you DO fit.

Now if we consider your example of 2 RTGs, providing 1.5 power per second. That would weigh 0.16 tons. For that weight, you could fit two solar panels and 2500 worth of battery storage. So 2 Z-1000s and 5 Z-100s, for 2500 charge and 4 power per second (versus 1.5), at the same weight. Or at a lower partcount, 1 Z-1000 and 3 Z-400s, storing 2200 charge at 0.015 tons less weight.

"Ahh but solar panels produce less power as you get further away" you say. Well, the scale factor isn't set up particularly realistically, so Solar Panels produce half power at a distance roughly equal to Jool's semi-major axis. So at Jool, those two solar panels would produce 2 power per second. STILL more than two RTGs. The '0x' point is set to 'almost 3 times Jool's Orbit'. In my game, right now, Eeloo is just a bit past its apoapsis and at a distance of 1.65 times the 0.5x distance. I'd guess based on the appearance that its apopasis is probably at or below 1.75 times the 0.5x point based on that number (it's really not that far past apopasis). I'm not sure exactly how the math works (the wiki says the falloff "follow a spline curve of 3 piecewise cubics defined from 4 points".) Based on that, I'd guess that a small solar panel array probably produces less power than an RTG on Eeloo only while it's on the furthest parts of its orbit. But then, I wouldn't generally advocate a solar rover anyway, because they spend so much time in the dark, so that mostly only applies to things orbiting Eeloo.

The point is, for most purposes, almost no matter where you go, RTGs weigh so much more than solar panels that you can AFFORD to fit enough batteries for normal operations, and still end up lighter.

Edited August 7, 2013 by Tiron

[Geschosskopf]

The point is, for most purposes, almost no matter where you go, RTGs weigh so much more than solar panels that you can AFFORD to fit enough batteries for normal operations, and still end up lighter.

But there's more to it than that. RTGs never run completely dry. Because they always provide at least a little bit of juice, you can get by with fewer of them than you might think. For example, built a small rover and put 1 RTG on it as its only source of electricity. You start out with your electric charge bar on the resource tab 100%. Now hold down W. The rover will accelerate to a high speed and will maintain this speed as long as there's anything showing in the resource bar. But the bar goes down fairly rapidly until it gets to zero. Still, if you keep holding down W, the rover will merely slow down to a lower speed, but will never stop. You'll see a tiny amount of bar flickering just above zero. This is providing the wheels with less juice than their full-power draw so they don't turn as fast as possible, but they still turn. And if you release the W key the charge bar will shoot back up to 100% and you can go fast again. Meanwhile, the lights never even flicker.

It's the same thing with reaction wheels. Maybe on paper using them would suck the charge down very quickly, but because the charge level is effectively never zero, they keep on spinning, although perhaps slower. But with rockets, you're not holding the control over constantly during a turn, you're just tapping it in the direction you want to go, releasing and drifting to where you want to be, then tapping again to stop the swing. Between these taps, the charge bar will refill entirely so each tap has the full power available. And for whatever reason, SAS never seems to lack for power when using reaction wheels to keep the rocket stable. This is probably also due to the fact that it's not using them constantly, but just doing a series of gentle taps, none of which use much juice and are far enough apart for the charge to rebuild anyway.

So, at the bottom line, 2 RTGs are enough, all by themselves, to keep probe brains alive forever, run however many lights 24/7 with no flickering, control the vehicle with reaction wheels, and keep it stable with SAS, all at the same time. No matter what the numbers say on paper, this is how it actually works. Could be this is an exploit, but I think it's really that reaction wheels and SAS don't need to draw their full load most of the time, and when they do it's only for very brief periods allowing recovery in between.

For the normal domestic electrical needs (probe brain, lights, SAS, and torque) of an airplane, a station module, or a rocket, therefore, all you need is 2 RTGs and could probably survive on 1. Thus, your argument of needing as many as 5 RTGs for such purposes is moot. It's only when you start doing things that impose high electrical loads for long periods (rovers going fast over long distances, messing with Kethane, using ion or electrical airplane/helicopter engines, etc.) that RTGs become inadequate.

Now I should note that solar panels without batteries can do the same thing as RTGs, always providing some non-zero amount of juice even if the momentary demand exceeds their output. But only while the sun's on them. So, if your only source of power is solar, you'll need enough batteries to meet the station's domestic needs all night long. Figuring out the number of batteries can be a chore because it depends on which planet your station's at and how you're orbiting it, and some combinations entail very long nights. You also have to remember to open the solar panels as soon as possible after launch, and retract them before aerobraking and such.

Sure, 2 RTGs weigh more than solar panels and batteries making the same juice, but for domestic needs the total of either is very small and the difference is just a fraction of a ton. This isn't enough to change the size of the rocket needed to move the station module wherever you're going with it so is a non-factor. But RTGs are low-polygon models with small, simple textures and no animations, and you generally need fewer parts with them than with panels and batteries. Plus they require zero intervention on your part. So for simplicity and less load on the computer, RTGs (for domestic use), seem the best bet. In which case there's no need for batteries.