Karcher RC3000: Battery Load Test

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Karcher RC3000: Battery Load Test

Postby robocleaner » March 25th, 2012, 9:54 am

This is a battery load test for the Karcher RC3000. It is identical to Vic7767's load test for the Roomba battery (see http://www.vic7767.com/how-do-i/).

UPDATED 29 MARCH 2012 - see "CYCLING UPDATE" below

Do not try this yourself unless you're confident in what you're doing - shorting batteries is dangerous


Background to this test

The need for this test arose due to a discussion regarding the impossible length of time Karcher RC3000 batteries seem to last. There are at least 6 members on this forum who have Karchers in excess of 6 years old, that are/were still working on original batteries. My oldest Karcher is between 6-7 years old, and cleans min 80sqm 2-3 times a week. Given that the Karcher returns to base to empty/recharge typically every 20-40 minutes, that's an awful lot of cycles over 6+ years... many, many more than the accepted 500-1000 cycles for a NiMh battery (up to 1200 according to Panasonic).

A member rightly pointed out that, logically, NiMh batteries couldn't possibly last that long... and he's right, in theory at least! So I promised to load-test my 6+ year old ones to see what they were still capable of...

PIC_0516.JPG
Karcher batteries made in EU by BMZ Germany


Test set-up

The Karcher was fully charged on its own base before the batteries were removed. Karcher uses 2 x 6v NiMh batteries at 1700mAh (10 x 1.2v cells) wired in series to give 12v at 1700mAh total capacity. To make this as accurate as Vic7767's accepted Roomba test, the batteries are wired in series and the load (lamp) is identical to Vic7767's - an MR16 12v lamp drawing 20watts (the Karcher draws 18w, so like the Roomba, its near identical to actual consumption of the robot itself). A digital volt meter is wired in parallel to monitor the voltage. The test cut-off I determined as 10 volts to make the test similar to Vics (although I'd usually cut-off at 0.9v per cell).

PIC_0509.JPG
Load test under-way

PIC_0512.JPG
The pliers are holding an insulated holder and not shorting the bulbs terminals!


Test results

At full charge, after 20 minutes rest, the batteries showed a combined total (series) voltage of 14.07v. The test ran until the voltage showed 10.00v. The time elapsed was 43 minutes. In theory, this means that the Karcher is still capable of running up to 43 minutes on 6+ year old batteries! Well, it impressed the heck out of me since my Karcher normally returns to base within 20-30 minutes, presumably to empty rather than charge! I have no logical explanation as to why these batteries can last that long after all these years, but the test clearly shows that they can (and frequently do).


Cycling to (hopefully) improve performance

Samsung quote their Navibot SR8855 battery to have a servicable life of 1 year. After 18 months, my orginal 14.4v/2000mAh Navibot battery was giving a poor 26 minutes maximum run-time. Cycling that battery increased that life to a consistent 67 minutes! So here I'm going to cycle these old Karcher batteries, then repeat Vic7767's load test and update the results - to see if these batteries performance/run-time is/can be improved. As the Karcher would charge these batteries in series, I'm going to cycle them in that manner too although better results would be likely if cycled individually.

PIC_0517.JPG
Karcher batteries set-up for cycling

CYCLING UPDATE 29 March 2012: Normally when cycling a battery you’d expect to see a progressive increase in the amount of charge being taken into and discharged from the battery pack with each cycle. That didn’t happen here. Over 4 consecutive discharge/charge cycles, these 6+ year old Karcher batteries returned a remarkably consistent 1470-1473mAh over each cycle - quite a high proportion of their original 1700mAh capacity. Repeating vic7767’s load test showed a marginal increase to 51 minutes (the maximum theoretical run-time of the robot). It’s not the dramatically improved performance you’d normally expect and usually obtained when cycling, for example, the Samsung Navibot battery which showed a more than doubling of run-time.

The Karcher does not drain its batteries once its finished cleaning as other robots do, but neither does it "max out" its batteries on every cleaning cycle. These unexpected cycling results lead me to suspect these batteries are indeed being “hyper-cycled” – a theory first suggested on this forum by Spirit Force. This is a methodology used by electrically assisted cars such as the Toyota Prius - frequent cycling in shorter bursts using just a small percentage of the batteries total capacity to prolong life well beyond the norm. Spirit Force has suggested a method to test/measure this theory which I will try, and update results here when I can: It may hopefully help explain why these batteries last so long! But for now I need my charger back to cycle my work tool pack batteries...
Last edited by robocleaner on March 29th, 2012, 1:56 pm, edited 2 times in total.
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Re: Karcher RC3000: Battery Load Test

Postby Fraggboy » March 25th, 2012, 10:40 am

WOW!! :clap:

Thank you for sharing that with us. I am shocked that the batteries are still giving that much run-time. But, then again. Nothing drains the battery while it's parked. After it's done charging, it parks. Then, when you want to run it again, it then empties out the dust bin (Unnecessary), and charges once more.

I can't wait to see if the 'run-time' increases after the cycling.

:thanks:
:D
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Re: Karcher RC3000: Battery Load Test

Postby mfortuna » March 25th, 2012, 3:34 pm

That is very interesting. One of the things I wonder about is if Karcher charges the packs as two x 6 cells or one x 12 cells. Based on my experience with 6 cell RC packs you can get a lot of life out of them if you don't over discharge cells. Over discharge is a lot easier with 12 cells than with 6 cells.
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Re: Karcher RC3000: Battery Load Test

Postby robocleaner » March 25th, 2012, 4:16 pm

It's 2 x 5 cells Mike, but good question; the charger/base outputs 24v with no load and the bot runs at 12v - it suggests the two 5-cell packs are simply in series. I'd need to open the bot and check the circuit to be sure though.
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Re: Karcher RC3000: Battery Load Test

Postby mfortuna » March 25th, 2012, 7:42 pm

Oops, I assumed it was 12 cells total when I saw something about 14V. Regardless of 2x5 or 2x6 that is very good battery life.
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Re: Karcher RC3000: Battery Load Test

Postby robocleaner » March 29th, 2012, 2:11 pm

For those interested, I have just updated my original post above with the results of cycling the Karcher's batteries.
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Re: Karcher RC3000: Battery Load Test

Postby Fraggboy » March 29th, 2012, 2:26 pm

Thank you for the update. From what I gather and understand (From your information), the Karcher is very efficient using the batteries over a longer period of time, thus the batteries are lasting longer. Am I correct to say that?
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Re: Karcher RC3000: Battery Load Test

Postby robocleaner » March 29th, 2012, 3:00 pm

I think it safe to say that the Karchers battery management is very well considered; the robot itself uses (almost) as much power as a Roomba whilst it's actually running. To me, the results of the cycle test were totally unexpected: These old batteries are in much better shape than anyone could reasonably expect for their age, and even when cycled they had nothing else more to give - it demonstrates to me that how they're being used/charged in daily use is excellent. Spirit Force's suggestion/theory/logic (by PM) is the only plausible explanation as to how the Karcher manages it...

The basis of the theory is here on the Toyota Prius chat forum: http://priuschat.com/forums/knowledge-b ... -life.html. Spirit Force PM'd me some Karcher run-time/capacity based calculations that suggests this could logically make sense. So I've got to test that out, haven't I? :lol:
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Re: Karcher RC3000: Battery Load Test

Postby Fraggboy » March 29th, 2012, 3:13 pm

robocleaner wrote:Spirit Force PM'd me some Karcher run-time/capacity based calculations that suggests this could logically make sense. So I've got to test that out, haven't I? :lol:


If you have time, sure!!
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Re: Karcher RC3000: Battery Load Test

Postby TechGuy » March 29th, 2012, 3:46 pm

Thank you for the information.

According to the graph on the PriusChat forum, if we want to extend the Roomba battery life span, we should limit each mission to no more than 25 minutes. Stop using lighthouse and give your battery much needed rest.

Roomba stops a mission when the loaded terminal voltage falls below 12V. What is the % depth of discharge when a cell falls below 1V?
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Re: Karcher RC3000: Battery Load Test

Postby robocleaner » March 29th, 2012, 4:19 pm

I don't think the theory quite works like that: It doesn't revolve around a fixed cut-off voltage, but a variable percentage of total battery capacity - the less capacity you use per outing, the longer the cells last. Using this methodology, Toyota offers a 10-year warranty on their NiMH Prius cells. The Karcher's chosen method of operation appears very similar from initial calculations, but I want to test that theory in the real world to either prove or disprove it.

I'm not a Roomba user (although Spirit Force is, and this is his suggestion/theory!) so I'm not familiar with Roomba's battery capacity/usage patterns. All I can say with a reasonable degree of certainty is that my Samsung Navibot equally hammers it's battery to death on each outing, then charges really fast and cooks the battery, and then continues to trash it by simultaneous draining and trickle charging on dock indefinitely thereafter... which is why Samsung only warrant it for 6 months and suggest replacement after 1 year... and why cycling it after 18 months extends the run-time from 26 minutes to 67! The Karcher avoids all of this "bad practice".

I'm not sure you could adapt either the Roomba or Navibot easily to change it's battery usage patterns; all I'm concerned with here is trying to find out why Karcher batteries do seem to last an incredibly long time when others don't. As yet I don't know what the depth of discharge/cut-off voltage of the Karcher is... those are two of the parameters I'll need to measure for the "hyper-cycling" test!
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UPDATED: Karcher RC3000: Battery Load Test

Postby robocleaner » November 19th, 2012, 8:59 am

Testing Spirit Forces' Hypercycling Theory

I did a more comprehensive response to this yesterday, but it got lost when the server crashed. In short, Spirit Force seems to be right.

The make date of this Karcher is 15th September 2005, so these original under-test batteries are 7 years 2 months old and still running well 2 to 3 times a week (comparable performance to my brand new Karcher). Voltage I measured by cribbing vic7767's Neato volt-meter idea using a lightweight/cheap voltmeter off ebay - accuracy checked against my Fluke, and in my case just blu-tacked to the Karcher since I'll be removing it. It's wired to the Karcher's Service socket VE+/- pins.

PIC_0609.JPG
Using vic7767's Neato Volt-Meter idea to test Spirit Forces' hyper-cycling theory.

The Karcher charges it's 12 volt pack to 15.5 volts. At 12.4 volts, it keeps cleaning, but hunts the base to empty and recharge - it'll return to base if it crosses the IR beam which projects up to 20 meters from the base... if it doesn't cross the beam, it'll keep on cleaning until it does. At 11.4 volts, it ALWAYS stops cleaning and just hunts the base, which, as the batteries are still highly charged, it can (reportedly) do for an hour or more (Note: the running load equates to a 0.6-volt drop with vacuum and all motors driven, so even in this state, the actual voltage of the cells is still actually 12 volts). Remember, the Karcher will also return to base to empty and recharge when the small 0.2l bin is full, so in practice the point at which the Karcher recharges its' cells is variable, yet the batteries never (hardly ever) fall below their full rated 12-volts (still 1.2 volts per cell).

This contrasts to (for example) the Roomba 14.4 volt pack, which consistently runs until the pack is depleated (1 volt per cell - technically empty). So yes, it does appear that light drain and regular recharging does lengthen the life of these NiMh cells.
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Re: UPDATED: Karcher RC3000: Battery Load Test

Postby robocleaner » December 13th, 2015, 8:56 am


10th Birthday Battery Update


I wrote:The make date of this Karcher is 15th September 2005, so these original under-test batteries are 7 years 2 months old and still running well 2 to 3 times a week (comparable performance to my brand new Karcher).

Those Ni-Mh batteries tested back in 2012 are now 10 years and 3 months old... and they're finally giving up. Voltage was still 6.99v & 7.24v after dock charging, but mission time was down to 10 minutes before it started hunting the base for a mid-mission recharge.

So, apart from a few plastic stabiliser springs at 1-euro a time after treading on the robot a few times over the years and one fall down the stairs, new 3rd party ebay batteries are the first replacement parts I've had to fit in 10 years. New batteries now fitted, and normal "still works as new" service has been resumed. Same 10-year old washable fabric filter, same 10-year old brush-roll (although I have just bought new spares just in case!).

The arguments made 10 years ago against the Karcher being far too expensive seem churlish now, when you consider the REAL cost per year of operation of those operating/maintaining/replacing Roombas and Neatos over a similar 10 year period. It also makes nonsense of the notion that you MUST have Lithium cells for long battery life... clearly Ni-Mh cells can last perfectly well when they're treated properly.

For those happy with a "bounce-around" type of robot, I find it a great shame Karcher decided to stop making the RC3000 earlier this year. :(
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Re: Karcher RC3000: Battery Load Test

Postby glnc222 » January 23rd, 2016, 1:32 pm

For comparison, the Neato Robotics vacuums maintained a margin of 30 per cent charge capacity against deep discharge similar to the Toyota Prius practice mentioned in the owner's manual. The 3200mah battery would use around 2ah before returning to base. Yet the battery is rapidly charged and maintained at full charge by periodic additional slow charges on the dock when the charge falls from self-discharge. The cells support only around 200 to 300 cycles in use, and the manual suggests 1 to 2 years lifetime depending on use. The margin against deep discharge is not enough by itself for long life.

The battery seems run close to its maximum charge and discharge rates supported.
The Botvac model switched from a 14.5v 12 series to 12v 10 series and a 3600mah capacity, in a smaller sub-C cell size from 18650 size.
At the sub-C size a lot of cells available do not support the discharge rate used and quickly wear out in tests I performed so some high drain type of cell is used. The 18650 sizes more commonly support higher drain rates.
Exceeding supported drain rates showed rapid wear on some AA size cells tested as well.

Some users report leaving the battery disconnected between runs and charging before runs instead of leaving on the dock to stay charged increases the lifetime. Exactly what lifetime in charging cycles is obtained has not been mentioned.

Regarding the Prius battery, I found the cells are very different, costing $25 each vs $3 and supporting huge drain rates over 100 amps, at the same voltage as all NiMh cells. Several hundred used in series.

The Karcher charging rate did not seem mentioned in the reports here, that is whether it performs slow charging which might be a factor in lifetime. One battery maker told me their specified lifetime referred to slow charging and discharging use, and the fast charging and high drain operations would be different.

Some users have thought the high temperatures to which the Neato cells are pushed in charging shortens the life. This is another feature of rapid charging, more than discharging. There is an inherent feature of rapid charging where the chemistry produces heat when approaching full charge, and the charger is controlled by temperature sensing. This is because of enclosing the cells in packs where the charger needs to terminate before the temperature gets too high, lacking cooling, compared to open individual cell chargers which go a little farther based on voltage instead of temperature. The NiMh cells drop very slightly in voltage at the maximum charge to control the individual cell chargers; chargers sense less than 0.01v shifts in voltage, and can be disrupted just by touching wires.

One type of AA cell sold is made for extremely rapid charging in 15 minute chargers, which heat the cells so hot they are too hot to touch. Around 8 amps charging rate is applied. Only a 100 cycle lifetime.

So batteries are made with a wide variety of characteristics for different uses and are operated in different ways with effects on lifetime. Lot of detail needed to evaluate a particular situation, hard to obtain information.
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Re: Karcher RC3000: Battery Load Test

Postby robocleaner » January 23rd, 2016, 6:23 pm

glnc222 wrote:So batteries are made with a wide variety of characteristics for different uses and are operated in different ways with effects on lifetime. Lot of detail needed to evaluate a particular situation, hard to obtain information.

Rather than look to Neato or iRobot for how their charging systems do work, the best source I found for how a charging system should be working to treat cells properly was from the cell manufacturers themselves - Panasonic (who also own Sanyo/Eneloop) are one of the largest and were a particularly good source of information. It's clear from what we do know about both Neato and iRobot charging that they both ignore best practice. But hey, it's only toxic landfill, it sells more batteries and increases their profits, so why would they care!!?

glnc222 wrote:Yet the (Neato) battery is rapidly charged and maintained at full charge by periodic additional slow charges on the dock when the charge falls from self-discharge.

The trickle/top-up charge is needed due to active circuit drain (scheduling function) rather than self discharge. Roomba and Navibot is the same. I remember Panasonic saying a very occasional trickle of no more than 20hrs was useful for balancing cells, but constant trickling was a sure-fire way to damage cells and prematurely shorten cell life. Karcher doesn't leave the bot on dock to trickle charge indefinitely (it has no active circuits to drain the cells when its not cleaning). It's that plus the fact it doesn't discharge the cells below the full rated voltage of 12-volts (10 cells) which is the key to long life - giving many many many hundreds of shorter (20-40 minute) mission cycles.

glnc222 wrote:The Karcher charging rate did not seem mentioned in the reports here...

Karcher uses an 18 volt 2-amp DC supply; on 1700mAh cells, it's >=1C charge rate - not a lot of difference to Neato or Roomba.

glnc222 wrote:One type of AA cell sold is made for extremely rapid charging in 15 minute chargers...

Bosch used to sell 15-minute rapid chargers for their 14.4-volt 2600mAh NiMh power-tool battery packs - that equates to a truly stupid 10-amp charge rate. It was trashing a number of those packs at £80 a time that first got me interested in cells... why they were failing so quickly (inside a few months) and how best to extend their life.
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Re: Karcher RC3000: Battery Load Test

Postby glnc222 » January 23rd, 2016, 11:08 pm

The trickle/top-up charge is needed due to active circuit drain (scheduling function) rather than self discharge. Roomba and Navibot is the same.

I thought that on the dock the Neato had Mosfet switches to power off the dock instead of the battery. It will run on the dock without the battery installed. A partial schematic was made of the system board at http://www.robotreviews.com/chat/viewtopic.php?p=132686#p132686
I have not analyzed it and maybe you understand that stuff more. It does seem odd that self-discharge would be high enough over just a day to warrant the topping off which occurs. Not continuous, but cycles at 0.5 amp instead of 2 amp. With the lithium charger mode set for Vorwerk models the periodic refresh cycles are omitted, and those cells do not self-discharge at any significant rate. That would require Mosfet power direction and they seem to have the same system boards, just different software.

I wonder if Karcher used any specially high quality cells like a more expensive high drain type or something.

It seems the fast charging used in the robots is to perform multi-charge runs to clean the house in reasonable time, requiring pushing the batteries beyond the most economical modes of use.
There is a note on the Powerbot that it will recharge only once for a scheduled cleaning on the same day. But then, it covers a large area on each charge, and has a larger capacity battery (taking longer to charge).
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Re: Karcher RC3000: Battery Load Test

Postby robocleaner » January 24th, 2016, 6:21 am

glnc222 wrote:I thought that on the dock the Neato had Mosfet switches to power off the dock instead of the battery. It will run on the dock without the battery installed.

All these active circuit scheduling bots are permanently connected and constantly charging/draining in some way. It's only when the battery is physically disconnected (usually by mechanical switch or removed) that the only drain is self-drain: As we know, the battery pack will stay charged for several months like that. I always physically switch my Navibot off between uses at the expense of losing it's scheduling and timer functions... that NiMh battery pack is now 5+ years old and still functioning well. As the Karcher has no active circuit/scheduling to maintain, it can sit off-dock between uses for several months - without removing batteries - also without draining its cells - and those NiMh cells lasted 10 years.

glnc222 wrote:I wonder if Karcher used any specially high quality cells like a more expensive high drain type or something.

My own experience with Karcher/Bosch (as Mike already suggested) is that the Germans do specify/select (perhaps even match) higher quality cells for their packs, whereas the many "copy" packs I've bought from the Far East tend to be a mixed bag: Some are good, but most generally don't perform as well or last as long. My 10-year old Karcher is now (since December 2015) running on a set of these replacement Chinese packs, so we'll see how they compare over time.
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Re: Karcher RC3000: Battery Load Test

Postby mfortuna » January 24th, 2016, 8:35 am

I couldn't find my original post but back in the day when NIMHs were used for RC racing, best performance was gained by using matched packs.

The cells are bought in bulk and are cycled three times. I believe most vendors used 5A charge and 30A discharge. The cells will fall into bins based on average voltage during discharge to 0.85V or 0.90V, length of discharge, and internal resistance. The best bins are sold at the highest prices. Racers bought the packs as 6 unassembled cells and built them into packs.

I did this myself with a bulk buy of 48 cells. I ended up with 2 great packs, 2 good packs, 2 OK but not great, one practice pack, and 4 leftover cells because 2 were defective.

Without matching who knows how the packs would have performed.
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Re: Karcher RC3000: Battery Load Test

Postby glnc222 » January 24th, 2016, 2:08 pm

What if Karcher had a balancer circuit inside their packs? That is not part of Roomba and Neato packs but seems mentioned more in connection to lithium packs, maybe where imbalance has more severe impact immediately.
Some users reported refreshing NiMh packs by disassembling and rebalancing when seemingly worn out.
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Re: Karcher RC3000: Battery Load Test

Postby robocleaner » January 24th, 2016, 4:07 pm

glnc222 wrote:What if Karcher had a balancer circuit inside their packs?

I personally don't think so, looking at the packs and the robot pcb. It really is just clean, simple, straightforward design and engineering. If you look at the photos above, the packs really are just clusters of 5 cells each. Also remember this robot was designed in the early 2000s, which pre-dates common use of lithium and that whole cell balancing thing which is normal practice now. I think Mike's philosophy is on-track - ensure the cells are reasonably well matched to start. When you start with good matched cells, if/when cells do start to fail, to then rebuild new cell(s) into an old pack is a pointless exercise.
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