Using NiCd Batteries

Mattymatt · September 2009

I am working on a solar project and would like to use dry cell NiCd batteries on it. From my research, it appears that most solar applications use some type of wet cell or lead acid battery. Will it be a problem to use NiCd batteries?

If NiCd batteries are an option, are there any commercially available peak power trackers that are compatible with them?

BB. · September 2009

Re: Using NiCd Batteries

NiCads are not cheap--and you may have to pay good money to "recycle" them when they eventually fail. You may also hit export/import restrictions (because of the cadmium content).

They have their advantages (have been used in aircraft because of their light weight and their ability to handle large amounts of current for short amounts of time)--I could see that somebody may find a need for them.

I am not sure that you would find "dry" NiCads in large sizes (probably more limited to smaller cells--but that is just a guess on my part).

What is your need/use that would be better served with NiCads?

In the end, you probably would need to talk with a battery supplier to find out if they would be a good choice for you.

-Bill

niel · September 2009

Re: Using NiCd Batteries

one of the members here does have nicds and i don't remember who it was. these aren't your standard aa, c, or d sized batteries he has though. just how large of capacity where you thinking?

Mattymatt · September 2009

Re: Using NiCd Batteries

Bill and niel thanks for the rapid replies!

I am trying to keep the weight down and I want the system to be able to withstand substantial temperature changes, thus my inclination to use NiCd. Would a different type of battery be better?

I'm doing this for a pretty small system (max power required ~300 Watts for 90 minutes at a time during the day and ~60W for 30 minutes at a time during the night). So I don't need too much power, and I was planning on simply stringing 20 D-cell batteries together in series (to create a 24V system). Would changing to fewer, larger capacity batteries be better?

I am currently trying to use a Morningstar Sunsaver MPPT to charge the batteries, but I am running into problems with charging the batteries. Since the MPPT was made for lead acid batteries, it creates a very high charge current. I like the MPPT and that it controls the voltage taken off the solar panels and maximizes my input power, but would I be better off with a different set up or are there MPPTs that are programable so that I could trickle charge my batteries?

Then I am also having some issues with the batteries discharging very quickly (I am getting approximately 1 Ahr out of batteries that are rated at 4.5 Ahr). Not sure why this is happening...

Any thoughts on any of the issues I am having would be greatly appreciated!

BB. · September 2009

Re: Using NiCd Batteries

I am no battery engineer--but Ni-Cads are pretty different beasts... The actually cool to around freezing during charging and then get to over 110F as they finish charging.

So, most "good" NiCad chargers have a temperature probe to detect full charge and/or detect that the charging voltage actually drops as the charge completes (battery voltage drops as it gets hot--called voltage depression).

I would be highly dubious that you can take a "standard" solar charge controller and charge NiCads (safely) with one.

Also, NiCad batteries are not very efficient at charging... At high charge rates (C/1 to C/0.24) you can get around 83%... However at low currents (C/5 for example) it drops to 65% or so. C/20 is down near 50%...

You can read a bit more about charging here. The NiCad wiki is interesting too.

I know that a Honda eu1000i generator (they are quiet and pretty fuel efficient) is probably not of interest to you--But if you are hauling around solar panels and expecting to recharge in a day--I am not sure what would work better for you.

Is this for hiking, remote instrumentation, or something entirely different? Unattended or tended, etc...

-Bill

niel · September 2009

Re: Using NiCd Batteries

i'm thinking maybe an fla battery may be better with needing 450wh of power. double that in keeping the dod at 50% for the fla value of 900wh. 900wh/12v=75ah minimally. those nicds are somewhat expensive too and after all is said and done you could have more available power from a cheap fla. fla= flooded lead acid.

Mattymatt · September 2009

Re: Using NiCd Batteries

Thanks for the information on batteries! NiCds really are different...

This is for remote instrumentation, something that I won't have to tend to for at least a year.

I was thinking that I could get away with a lower capacity battery because during the 450 wh load, I could run the majority of it directly off the solar panels. My major requirement would simply be the night requirement of 30 wh (which at 24V is just above 1 Ah). Do you still think that a fla would be best?

mike95490 · September 2009

Re: Using NiCd Batteries

Mattymatt wrote: »

Thanks for the information on batteries! NiCds really are different...

This is for remote instrumentation, something that I won't have to tend to for at least a year.

I was thinking that I could get away with a lower capacity battery because during the 450 wh load, I could run the majority of it directly off the solar panels. My major requirement would simply be the night requirement of 30 wh (which at 24V is just above 1 Ah). Do you still think that a fla would be best?

Unattended for a year = AGM batteries & charge controller set for AGM w/BTS.
Solar panels only provide power 5 or 6 hours of a sunny day. What do your instruments do the rest of the time? 4 cloudy days, and power fails, what happens then? Will it re-boot on its own when sun comes back?

BB. · September 2009

Re: Using NiCd Batteries

I agree with Mike--AGMs, sized for approximately 3 days of no sun, and 50% maximum discharge (6x daily load).

Another major design issue is where will the system be installed. Weather (and even local weather) patterns will help decide the size of the solar panels.

And knowing what your system will do on cloudy days -- suspend operation, or it must operate. If it must operate during bad weather/winter, then you are looking at adding panels (and batteries)--or even an auxiliary power source (auto start genset, or something).

Also, you may need to remotely monitor battery bank performance--A battery monitor type device would help. I don't know if you can find one that can be read via a remote interface--or if you would have to build your own (for such a small system).

Can get very complex and expensive very quickly--again depending on your needs.

-Bill

westbranch · September 2009

Re: Using NiCd Batteries

Hi Matt, sounds like you really do need to talk to a factory rep.

Use this link:
http://www.saftbatteries.com/Contacts/tabid/72/Language/en-US/Default.aspx?TYPECTL=MAP&ZONEID=6

or this one
http://www.saftbatteries.com/

to try finding a local regional rep for SAFT, they make all types of Ni Cd's and can give you good advice for your particular application.
The first question they will ask is about the application field (type) as they have different divisions.

Good luck,

Eric

Mattymatt · September 2009

Re: Using NiCd Batteries

So the system I am designing is an attempt to create a low cost satellite power system. Thus I never have to worry about clouds and don't need as much of a storage ability. My main concerns are ability to handle temperature extremes (-20 to 50 degrees C), I would like to keep the weight to a minimum (no more than 5 kg), and if it is possible, I would like to keep the price reasonable. I'm okay with a moderate amout of complexity in the system. Does this change any of your recommendations?

mike95490 · September 2009

Re: Using NiCd Batteries

Mattymatt wrote: »

So the system I am designing is an attempt to create a low cost satellite power system. Thus I never have to worry about clouds and don't need as much of a storage ability. My main concerns are ability to handle temperature extremes (-20 to 50 degrees C), I would like to keep the weight to a minimum (no more than 5 kg), and if it is possible, I would like to keep the price reasonable. I'm okay with a moderate amout of complexity in the system. Does this change any of your recommendations?

Clear as mud.

If you are beaming power from a Sat, why have PV or batteries. Just need your Rectenna and wires.

Mattymatt · September 2009

Re: Using NiCd Batteries

I'm not beaming power anywhere...all the power stays on the satellite. sorry for the confusion.

mike95490 · September 2009

Re: Using NiCd Batteries

Mattymatt wrote: »

I'm not beaming power anywhere...all the power stays on the satellite. sorry for the confusion.

Lithiums are all that are used in sats. They have very expensive ones that can cycle thousands of times. Maybe you could use Optima spiral batteries, but I think they will fail long before the sat is ready to come down.

What's the life time of the sat ? That's what decides the battery chemistry.

How often are eclipses, every 90 min, for 90 min, Geo Sync , 24 /24 The blackout time sets the size of the battery.

BB. · September 2009

Re: Using NiCd Batteries

oops... Answered an entirely wrong question.

If this is a space based application--you really need to work with a battery vendor that is rated for space. The issues with vacuum, radiation, outgassing, thermal extremes, reliability, etc. are not something that are answered here very well.

-Bill

Mattymatt · September 2009

Re: Using NiCd Batteries

The goal is for the satellite to last for around 1 year, in a LEO orbit with 30 minutes of eclipse every 90 minutes. NiCd have been used in space applications (and they appear to be simpler and cheaper than Li batteries). This is why I was looking for an MPPT that worked with NiCd...any recommendations on companies to talk to (for either the MPPT/charge controller or the batteries)?

westbranch · September 2009

Re: Using NiCd Batteries

again, look here

http://www.saftbatteries.com/MarketSegments/Space/tabid/152/Language/en-US/Default.aspx

note the market segment = space

ej

niel · September 2009

Re: Using NiCd Batteries

as far as what is used for controllers and batteries in space is something most of us aren't familiar with as it is most likely specialized. the solar applications we deal with here are terrestrial. in what capacity is the payload designed to work. ie, ham radio, sat tv, gps, etc.? i would also think you'd have a better handle on what could be used and where to get it if you can have something to go into space. no friends at nasa or the eu space agency?

Mattymatt · September 2009

Re: Using NiCd Batteries

I didn't want to scare you all away by saying that it was a space application. I know very little about operating a solar powered system, and was very appreciative for your help in those matters. I need to create a working terrestrial system before I can get anything for a space system. So any ideas or suggestions you might have are greatly appreciated! Even if it is simply the terrestrial version.

I will begin talking with the people at Saft Batteries. But any advice or suggestions (particularly of NiCd compatible equipment) is greatly appreciated!

BB. · September 2009

Re: Using NiCd Batteries

Frankly, we don't want to lead you astray on the space application--few of us here have any experience in that area.

For charging optimally--you can look at a current mode switching power supplies... They can be pretty efficient and easy to get pre-built assemblies, or build from parts (sometimes, you can even get an evaluation board from an IC vendor and just populate it with the misc. components around the central IC).

Here is an IC from Linear Technology that would almost work (16 cell max?)... There are probably several ways "around the limitation". But it gives you an idea of what to look for and there is an evaluation board available too.

If you are dealing with solar panels... Study their IV curve (current/voltage)... Here is a nice random Solar Panel spec. that has most of the major silicon curves nicely plotted (voltage, current, power, lumens per sqm, temperature, etc.).

One of the big issues with solar panels is their Vmp (Voltage max power) changes with temperature--Hot panels have a lower Vmp VOLTAGE, hot panels have a lower Vmp Voltage... So--depending on how much you want to optimize your system--You may get 15-30% more power in cold weather with a Maximum Power Point Tracking based charge controller (MPPT) vs a simple "on/off" Analog controller.

If you want to design a MPPT controller--you need a fair amount of electronics experiences (good chips and design guides can help). The MPPT controller is (usually) a "Buck Mode" switching power supply which can take "high voltage/low current" and (like a DC Transformer) transform the energy to "low voltage/high current"... Connecting this all together and putting a microprocessor to control the Pmax=Imax*Pmax equation is not easy--and (I am guessing) even good engineers with lots of experience have to work hard at getting one to work well.

In the end--what is it you are looking for? Maybe we can help if we know more about your project and/or what you need the "supply" to do.

-Bill

mike95490 · September 2009

Re: Using NiCd Batteries

BB. wrote: »

One of the big issues with solar panels is their Vmp (Voltage max power) changes with temperature--Hot panels have a lower temperature, hot panels have a lower temperature...

This is really weird, I thought hot panels were always sold out.

BB. · September 2009

Re: Using NiCd Batteries

Alright--who edited my post to make it look stupid... One of you guys...

-Bill

westbranch · September 2009

Re: Using NiCd Batteries

actually it is better than the original..

not me though....

ej

Using NiCd Batteries

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