Battery Replacement/Rewire

[Della and Dave]

Thanks for all the info. After reading what you guys wrote, and doing some additional reading, I think it's best to say goodbye to our old flooded lead acid start battery.  It's the same age, at least I think, as the dead golf cart batteries, and while it hasn't failed me yet, I don't want to end up three fjords from civilization with bad weather coming and not able to start the engine.  Once you get one fjord over from Resurrection Bay, you can't get the coast guard on the VHF. I like to at least plan to be able to deal with most things myself anyway. You can always set off the EPIRB, but I wouldn't want to do that for a dead battery.  I would have to buy too much beer if I did that.  Plan B should never be "call the Coast Guard", that should be at least Plan F or G.

I think that means a new AGM start bat, but how big should I go?  The current one is a group 27, around 90 AH.  Strictly from a "fits the space" standpoint, I am considering another Mastervolt Slimline in either 150AH or 200AH, but that seems a little overkill for a start battery.  They are pricey, but little extra reserve capacity isn't a bad thing.  Any opinions?

I'm a little hesitant to add the extra complexity of an inverter.  I don't have anything we really need that runs on 110v power.  Our water heater is plumbed to take engine heat, or electric.  It seems extravagant to heat that with batteries.  Most of my boat tools are battery powered.  Recharging tools would be one use, but I do have a 750W portable inverter if I need it.  They are mostly charged at the dock anyway.  We heat with a Sigmarine Diesel heater that takes a little 12v power for the fuel pump.  A circulation fan is nice to run to even out the temperature in the corners, but that's 12 V as well. 

In my reading, there were quite a few very negative comments on the Xantrex charger and inverter, mainly about durability and support.  I always take them with a large chunk of salt, but there were several, and they were specific about their problems.  With electrical stuff, you never know if improper installation was why it stopped working.  Any insight if Xantrex is having quality issues?  In general, I prefer U.S. made where practical, and MasterVolt is, but I couldn't find where Xantrex was built.  I like the ability to remove the control panel and put it where you can see it conveniently.  I would prefer separate outputs for each battery bank, and I would also like the ability to use input power other than 110v 60 Hz.  The Mastervolt has both those features, but it's remote display isn't so great.  That means sticking your head in the locker to see what is going on with the charger.  Still a lot better than what we have now. 

I'm hoping that this installation will suffice when we eventually cast off and do some long distance trips, but I'm not opposed to adding an inverter at that point.  That might argue for going with the larger capacity charger though. 

An a related topic, our battery switch has a placard that essentially says start with the switch on both and don't change it while the engine is running.   Does anyone know why?  I was sort of assuming because you had a start battery, you would want to start with that battery.  That way you would know if it is Kaput.  If you never start with only the start battery, it could be dead for a long time and you are really starting with your house bank and not realizing you have a dead start battery, which, come to think of it, might be where we are.

[Della and Dave]

One other tidbit of info.  According to the shop manual, the starter on the Perkins 108 has a max current draw of 900 amps.  The 200 amp hour AGM battery I am contemplating has Cold Cranking Amp Rating of 750 amps at 0F, and a Marine Cranking amp rating of 1,250 amps at 32F.  

That would seem to indicate that at 0F it wouldn't quite supply enough without help from the house bank. At the Marine cranking Amps temperature, should do fine.  The max draw is just the peak, so it might still be fine a few milliseconds after you hit the start button.  In addition, as the battery provides current, it heats up.  For us up here, the chances of wanting to start at a temperature of 32F or below are pretty good, but 0, the harbor is usually frozen over. Might not be quite the same issue down south where the palm trees aren't plastic.  

[PeteW]

I've been buying case 31 size AGM batteries from Sears. Don't laugh. Their deep cycle marine battery as you expect is dubbed  the"Die Hard". It is actually manufactured by Odyssey.  Aside from making all the AGM batteries for the military they private label to Sears. Their AGMs are good to -40 degrees C and the 31 will provide well over 1000  cold cranking amps. Here's the link to the catalog.

http://www.odysseybattery.com/documents/US-ODY-TM-001_0411_000.pdf

I replaced a 27 frame sealed lead acid from West Marine with a 31 sized AGM and the increase in RPM at which I could crank was significant. I like the 31 because its the largest battery I can physically lift without a crane. Around 90 lbs. Typically cost $300 but goes on sale once and awhile. Sears gives me 6 months same as cash on them if you have a charge card.  Pete

Forgot to mention the issue with flooded batteries and cold is the freezing point of the electrolyte increases as the charge decreases.  Why I store my tractor batteries in the basement during winter. Might explain why your golf cart cells are dead or dying.

[Della and Dave]

Thanks Pete.  After I read your link, I went back to the Mastervolt site and realized I made an error, so I corrected my post.  Their cold cranking amp rating was at 0F and Marine CCA is at 0C, (32F). I think that means I wouldn't have an issue cranking with either battery.  When I compare the Diehard/Odyessey it seems like either would work, but the Die hard is cheaper and has better Cold Cranking Amps, but lower total capacity in amp hours (100AH vs. 200), and I am going to have more of an issue with modifying the battery box.  As fate would have it, I was just installing a new Odessey spiral battery in the car this evening. 

In the end, shipping cost may be the decider, getting lead to Alaska costs.  I had one really negative experience with Sears not installing the cotter pins on my tie rods and loosing my steering at 65 mph, so I am not a big Sears fan.  It wasn't a disaster, but really scared me and the guy was arrogant and didn't take responsibility. 

[Dale Tanski]

First off I found this article and found it very informative regarding batteries. Worth the read...

http://www.yachtsurvey.com/boat_battery_basics.htm

To answer the question of why it is a no-no to switch the battery selector switch while the engine is running, the answer is as follows.  There are several designs of battery selector switches.  The basic switch gives the ability to select one of two battery banks individually, a position to select both banks combined and an OFF position.  The issue becomes how the positions on the switch are configured and how the switch mechanically gets to those positions. 

If the switch is physically laid out so that while switching between banks of batteries and combining them (both position) the switch does not pass through the OFF position, that is a good thing.  While the engine is running and the alternator is turning generation power, if you disconnect the connection to the battery it can damage the alternators diodes.  A diode is an electrical device that does the same thing as a check valve in the plumbing world or a ratchet in the mechanics world.  It allows the flow of current (water for you plumbers, and spin direction for you mechanics) in one direction only. 

An alternator actually develops AC current (alternating current) when it is operating which is not compatible with your DC current (direct current) batteries.  By installing a set (4) of diodes in the output circuit of the alternator known as a diode bridge, the diodes modify the AC current into DC.  The problem occurs when you switch you battery selector switch to or through the OFF position.  The diodes see the disconnect as an infinite load.  Diodes are designed to handle a maximum load rating, much like each of us can only hold up so much weight.  If the weight was say instantly doubled, you would drop the load. In the case of the diodes, when the load heads towards infinity if even for an instant, the diodes drop dead. 

If the switch is laid out so that you pass through the OFF position while changing banks and the alternator is running, you kill your diodes.  Some switches are designed that way and some are not.  The next issue is how the switch contacts are designed inside the switch.  There are two types. One is a break before make and the other is make before break.  The first, break before make, means that the electrical circuit is disconnected to the load as the switch is physically moved before it connects to the next circuit.  The make before break means that the first circuit is maintained while the switch is physically moved to the next circuit. For a short moment of time, both circuits are connected before the first is disconnected and the second is left connected on its own.  This area where the both circuits are in play is the "both" position. 

You can check the design of your switch easily.  With the engine OFF and your cabin lights ON, slowly switch your battery selector from the 1 position to the 2 or perhaps your BOTH position. If the cabin lights dim or go off and then back on, your switch is a break before make and a diode eater.  If your lights stay on, your switch is a make before break and you can select what you want without damaging your alternators diodes as long as you do not select the OFF position.

If you find you are not happy with the design of your battery selector switch and you have the desire to upgrade, I would recommend looking into the Blue Sea line of switches.  They make several configurations of battery switches besides the standard 1 - OFF - 2 - BOTH.  Another great design feature is that they incorporate glow in the dark dials. Now this might not be such a desirable thing in the land where the sun never sets for half of the year, but for the rest of us it is nice to have the main switch easy to find in the dead of night.

As an aside... You have headed over a slippery slope.  Yes the design of the electrical system is very important. Yes the type of batteries are very important, but so is the proper selection of wire, connectors, buss bars and all the rest of the associated components.  Just like your missing cotter pins, if you miss even the slightest detail you may encounter an unanticipated outcome.  I would recommend solder on lugs for all of your battery cables.  Install fuses in your battery leads. Install covers and insulated partitions to protect against accidental short circuits.  A misplaced aluminum boat hook will cause big problems if it comes in contact with battery connections.  Wire gage is a huge factor.  Determining wire lengths for DC circuits is different than for AC wire circuits when allowing for voltage loss.  As you mentioned you are talking hundreds and hundreds of amps, too small of wire and think glowing wire like in your kitchen toaster.  Bigger is better is a great rule to live by while selecting components in an electrical system.  The sting of the shipping cost will quickly be forgotten while watching a burning boat. 

Dale

[Della and Dave]

Thanks for the explanation of the reason for the switching prohibition, it makes sense now that you explain it. I assume I still have the internally regulated diode bridge inside the alternator, but to be honest, I'll have to check.  I'll do the test on the switch when I am at the boat next to see if it is the make-before-break type or not.  Even if it isn't a break-before-make, and as you put it, a diode eater, it seems like a good practice not to switch anyway, you never know when a bit of corrosion or grit could be in the contacts and cost you a diode bridge. 

Your point about wiring is well taken.  That's one of the reasons behind taking this on, it's currently a mess.  As an example, I have 9 wires off the common post of my start battery right now .   Those will go to a bus bar.  I also have some red wire on the common side of the system. You can tell Pete is an Engineer by his schematic, he lists the wire gages , that's really helpfull, although our setup won't be exactly like his so we may need to deviate some. 

That's part of the reason I'm researching this now to be honest.  Once I tear into it we'll be out of commission until the project is finished, so I want to have it as close to spec'ed out as I can before I start as I can so I can order the right parts. When he parts store is 300 + miles from the boat! planning is key.  That means starting with the capacities of stuff like the starter, charger etc, and sizing wire, fuses, buss bars from there.  Eventually, I'd like to end up with a schematic for the boat. 

We also have an anchor windless that needs power that I have to address.  Since we have to anchor deep, it's really almost a necessity.  I know some folks that use them as pot pullers for shrimp pots as well, and we might give that a try for fun, but it is a power pig, up to 60 amps at full load. 

[PeteW]

I'm using a Sterling Pro Reg B external smart regulator on a Large Frame 100 Amp Ford Alternator. The regulator has a sense wire so over voltage is not an issue. If I switch it into an open it will shut down and issue an over voltage alarm. Somewhere around 16 VDC.

That being said, what it fails to provide is a means to fold back on over current. Initially I had a problem with the alternator belt slipping at around 60 amps. So I converted it to dual V belts.



Westerbeke wanted $630 for a dual pulley for the Westerbeke water pump. I was able to retrofit some small block Chevy hot-rod part on there for $18.00.  No more belt slippage. To test this system I ran the house batteries down and started the motor. Here's what happened when the Sterling Pro split R switched the  load to the dead house bank.



I don't know what the actual alternator output current was before I shut it down but it would appear to have pegged that meter and bent the needle at well over 120 amps. I know the alternator got hot as a pistol in about 2 minutes. I have since replaced that meter with a 250 amp shunt and a high quality 250 amp meter movement.

I suppose this demonstrates why perhaps some don't recommend  switching battery load in while the alternator is running. With a proper alternator regulator it is not only possible but a necessary reqirement under normal operation.

So far I have only found one company with such a device that provides smart regulation and current fold back. That would be the Ample Energy V3 marine external regulator with adjustable current limit. So with that device I could switch in a dead battery bank without fear of taking out the alternator. I think you should be able to do that. Otherwise what good is it when you're out there with dead house batteries?

Incidentally I'm quite certain that its the single belt that allows the standard Westerbeke 55 amp alternator to current limit. At 55 amps the belt simply starts slipping thus limiting the current.

Also most 70 and 100 amp press in diodes can handle peak currents of over 200 amps and a PIV (peak inverse voltage of well over 100 volts. Its excess heat build up from forward IR drop that takes them out eventually. The harm in switching your batteries out while the alternator is running is it can take out your sensitive electronic gear. The alternator will most likely survive.

Pete

[Della and Dave]

Ok, so this is long, sorry about that.  I'm recovering from knee surgery and using the time to plot boat projects. 

Pete's pimped out charging system got me thinking.  One of the goals I had in getting into the battery thing is to improve access to the alternator and port side of the engine.  (As you recall from our posts last year, the water pump access gave me fits).  It's a project or two into the future, but I am also thinking that upgrading our alternator would be nice down the road.  Eventually, we would like to go cruising, around 2020, or so, and current mods to the boat need to support that goal but let us sail and learn what we are doing in the mean time.  Our very limited experience would support what Pete said; at full engine RPM, our properly tensioned belt (at least as far as I can tell) slips.  I think we have a 55 amp alternator, but I'm not sure.   

So, how much horsepower can you get out of a single belted system, before you have to pimp it out like Pete?  If dual is good, would triple be better, what about modern automotive serpentine belts, and can you get a water pump pulley or crank pulley for those?  I tried to find some answers. 

An alternator's efficiency is about 60% according to the DelconRemy white paper at http://delcoremy.com/Documents/High-Efficiency-White-Paper.aspx.  (I found it to be a good read along with the battery site Dale recommended).

There are 746 wats in one HP.   Power in watts is volts x amps

A 55 amp alternator with an efficiency of 60% running at 14 V therefore requires:

(55 amps/.60)x14v=1283 watts

1283 watts/746 wats/hp=1.7 hp.  (what I currently need, and almost have, but it slips).

So if I wanted to hot rod the charger, how many belts would I need for say a 100 amp alternator, or a 150, or why not go for broke and do a 300?  More is better right?  Not so fast...... 
The book on my batteries says they can take 58 amps each max charging current, and not for the whole charging cycle, only in bulk charge mode and that is only for deep discharge that will toast your battery if you do it too often.  If it were divided evenly, that argues that there wouldn't be much point in anything over 116 amps, unless we were to put in a larger house bank at some point, and maybe that would be desirable. More is better right???

It seems like a water maker would eventually be nice, but it also adds a lot of draw, so it would be nice to be able to feed it without having to run a generator, if you have a big alternator and some inverter capacity to take up the start up surge for the motor.  Rich Boren, of RO water maker fame, says that works in his video, and he did it on a 365.  He says a Honda 2000 generator works well (not the knockoffs though). At 12v, 2000 watts is 166 amps.  (A little left over for charging etc, but it really only can sustain about 1600 watts.). That seems to argue for an alternator somewhere in the 200 amp range, pretty big. 

Here is where I got lost in the sizing.  Reading up on V belt stuff, I found out power transmission depends on a lot of factors, some of which I don't know. Some of them are:

Pulley material, aluminum is not as good as cast iron, but is lighter and easier to machine. 
Diameter of the pulley
Type of V belt, and there are a lot of options
Degrees of wrap
RPM
Type of load, I assume an alternator isn't too bad because at startup, the electromagnetic torque is low at low RPM and builds as RPM increases. 
Belt tension.
I tried to size belts using the charts I found to see how big you could go with a dual V belt, but struck out.  Maybe I need another beer. 

To me, experience trumps theory, so Pete's experience, and our limited experience, as well as a couple of other people speak up on blogs say that the limit of a single V belt on a Westerbeke is a little less than 55 amps.  So does that mean Pete's setup could go to 110, but would then slip?  When is it putting too much load on the bearings on the water pump and or crank?  Two belts doubles the bearing stress at least.  Are there other factors involved, are two belts twice as powerful as one?  The other question is, in practice, do cruisers need big alternators, or are solar panels and wind generators better choices?  Anyone have any real world advice for how big is big enough?  Is sizing it based on a water maker foolish to begin with?   

Any thoughts? 

P.S. Nice setup Pete. 

[Dale Tanski]

I wrote a response to this post the other day but hit the wrong button on the way to post and lost the whole kitten kabodle.  So here we go again...

I would strongly recommend that you indeed design your electrical system for the installation of a water maker if that is in the cards down the road.  If you design for what you have now and go to add the water maker at a later date it will only cost you more time and most importantly more money. 

When it comes to the V-belt drive that connects your alternator to your engine, there are many items to take into account.  You thankfully hit on many of them but I will try to elaborate.  There are design tables supplied by the manufactures of belt drives that will allow you to select the proper size belt cross section, the size of the pulleys (sheaves) for the selected ratio and if you know the dimensions between the shafts it will even supply you with the proper belt length. 

I have a very similar system to Pete's.  I turn a 110 amp Balmar marine alternator that has its own internal regulator, however I regulate the output using a separate stand alone smart regulator also made by Balmar.  One of the reasons is that the smart regulator does not load the engine for several seconds (programmable) which allows the engine to come up to operating temperature and RPM.  It also ramps up the charge rate so as not to shock the drive system. 

When I was designing the system I recall that a single belt drive was only good for around 50 amps.  This means that the average single belt drive arrangement can only transmit the amount of horsepower that is required by a 50 amp alternator.  By adding a 2nd belt I was able to effectively transmit the required horsepower to handle the 110 amp alternator. 

The sheave material that is utilized is somewhat important but only in marginally preforming drive systems.  Cast iron is the best material as it is a porous and thus has a higher coefficient of friction.  Aluminum tends to polish itself and the coefficient of friction drops as time goes on. 

The diameters of the sheaves are more important.  For the most part the larger in diameter the better as they provide more surface area for the belt to grip.  In my case I modified the diameters of the sheaves from the factory arrangement.  Diesel engines run relatively slow compared to their gasoline counterparts and we tend to run our diesels at lower RPM's seeking smoother quieter operation.  I designed an overdrive system where the alternator spins at higher RPM's than it normally would. In this step up ratio drive by installing a larger diameter crankshaft sheave the alternator spins at even more revolutions. 

Adding a second belt allows more HP transfer. The Perkins (modified for marine use by Westerbeke) has plenty of horse power to power all of your accessories.  Where the engine suffers is that to transfer that horsepower, there must be adequate belt tension.  Perkins put out a tech bulletin that warned about putting too much side load on the crankshaft. Excessive belt tension was causing crankshaft failure between the main journal bearings.  With every belt you add comes with it the tension of the belt.  Too much and you break your crank so I would stay away from more than two belts.

You mentioned a serpentine flat belt drive that are typically found on automobiles today.  Flat belts have much more surface area than a V-belt and they typically transmit more horse power and require less belt tension to achieve that transfer.  There is a company that produces serpentine belt drive systems for marine applications but they are pricey. 

Alternative energy for the most part is a looser.  What I mean by this is that solar for instance has the highest dollar for watt ratio out there.  I just got a quote for installing solar on the roof of the store to supply my electrical needs for lighting.  The quote came in at $102K. After state and federal incentives, my out of pocket expense would be $63K.  If you do the simple math it would take 15 years to pay this cost off if money cost nothing.  I figured out that the materials only cost $35k.  On top of that I would have to declare the government incentives as earned income.  NOBODY thinking from a return on investment would install that system. 

Wind turbines tend to be noisy and require maintenance. In both cases, solar and wind you have to wait for the wind or sun to provide while your food rots.  If you are going to be sailing I would recommend a aqua generator.  It is simply a generator with a propeller that you tow behind the boat that charges your batteries without noise.  The cleanest most cost effective energy source is your shore power plug.

Dale

[SVJourney]

D & D,
You asked for users actual experiences with the Beke, so here's ours:

We have 5 27series batteries for ~500 amp hours on the house bank.  Max charge when severely depleted is ~ 65 amps @ 1600 rpm. 
We have a 110amp Balmar alternator on a single belt.  We use Gates green stripe belts and they last about 400 hours before they start to slip.  I would not shell out for dual belts as the cost to advantage isn't worth the price. 
If I had a bigger bank, I would just throttle down for bulk charging to reduce the load on the alternator.   

[Dale Tanski]

The question is.... why is your 110 amp alternator only putting out ~65 amps? 

1) RPM not high enough?
2) Belt slipping?
3) Under sized wiring?
4) Regulator not set up or not correct?
5) Temperature sensor control on battery bank has a problem?

If I were to guess, I would say that the belt is slipping self regulating the output of the charging system.  At the 400 hour mark the belt begins slipping to the point that it is noticeable. I remember ~50 amps and D&D say 55 amps. It would no surprise me that the slip load on your alternator at the belt tension that you can maintain is 65 amps. 

My 110 amp alternator will put out 110 amps until the temperature sensor in the alternator throttles the system back to save the alternator or the battery temperature does the same.  Because I utilize AGM's the charge load is infinite. 

Dale

[SVJourney]

My thought is that the bank will only accept 65 amps max, even when depleted.  Anyone else want to weigh inmon this?  Flooded cell, 5 group 27 batteries.

Wayne

[PeteW]

Wayne,
Everything Dale just said with the addition of  6) High internal resistance in the batteries. 7) your current meter is no good. Those automotive ammeters are crap.

I can only guess what's wrong as well. First thing is to get out the volt meter. Measure the voltage at the batteries before you do anything. Next measure the alternator voltage across the alternator with the motor reved up. I'd expect to see at least 13.8 volts. If the Balmar regulator is into some charge profile I would expect 14.5.

If that checks out, measure the voltage at the batteries. It should be within 3% of what you measured at the alternator. If not your wires gauge is too small. Per ABYC Standards, you should have AWG #2 in your 110 amp charging circuit from alternator terminal to battery bank . Don't forget the return ground directly to the alternator case ( not the engine block).

If it checks out get a  clamp on amp meter to verify what the current really is. Your should be using a quality meter with a calibrated shunt. Running wires to an from a panel mounted ammeter at 110 amps is a no-no.  If the current is low and the voltage is high, get your batteries tested for high internal resistance.

You can tell if the belt is slipping by looking at the engine tach.

If you voltage is low at the batteries make sure the sense wire to the balmar regulator is connected directly to the battery bank with its own wire. If you don't have a sense wire and or if you have diode isolators, that can render your charging system ineffective.

If you resolve something repeat the above exercise over as there may actually be multiple problems. And you may be looking at to some extent why I'm not that wild about wet cell batteries. They tend to be soft even when they are still considered good. Meaning the drop down when you load them and they float up when you charge them but they don't deliver or absorb much current. That's the high internal resistance.

Pete

[Della and Dave]

I dug into the Balmar 6 series 100AMP 12V alternator and plotted the power output vs alternator RPM data.  (I used 100 Amp instead of 110 because they had data for it)  As you can see, there is a pretty significant difference between hot and cold.  The RPM of course makes a significant difference.  They offer several pulley options, single, double and serpentine, with a kit for the Perkins.  They recommend a double or serpentine over 100 Amps.  The combined effect of lowish RPM, and running hot, could explain a lot of the Wayne's missing amps.  Especially if you add in a little extra battery resistance and/or connection and cable resistance. 

[Della and Dave]

Thanks Wayne, Pete and Dale. 

Wayne, by the numbers I was calculating that you would need somewhere close to 4 hours to recharge based on your post.  I figured a 50% discharge, so 250 amp hours at 65 amps, with about a 10% loss in the system.  At 1,600 rpm, I would guess the Beke would burn a little over a gallon in that time.  Is that the way it really works or does the charge rate drop off as the battery fills up?  (Nice post on your web site about going through the canal!)

Are you using solar, wind or water power to supplement your power needs?  I read that you had some solar.  How much does that help out in practice? 

At what point would it be better to just use something like a Honda 2000 generator, and save the fuel and wear and tear on the Westerbeke?  A Honda could put out 1600 watts at 13v so about 120 amps, or roughly double what my alternator could do, and use less than half the fuel. The downside as I see it is weight, and you would have to carry gas or do a propane conversion. Upside is they are quiet, and only half the time listening to an engine, plus flexibility.  Some people have safety concerns about using them underway, but it sounds like a lot of people do it at anchor. 

Dale, I was reading about the water generators, and it sounds like they work, but you can loose then to marine life, or trash, and they have some maintenance issues too. They also don't work if you aren't moving, so if you are anchored, no power.  Do you know how practical they are in real life?  There is a lot out there on the strengths and weaknesses of solar and wind, but less on water generators. 

I was reading the Westerbeke manual, and one option in the book is to add another alternator, doubling the capacity, by adding another alternator instead of installing a single larger one. The voltage regulator would have to change, but the company Pete mentioned makes one that can handle two alternators, and I think Balmer does according to their web site.   Because the extra alternator is on the other side of the engine, some part of belt load would cancel the first, alleviating the crankshaft stress some.  That would put it on the Starboard side, and space would be an issue, on Polaris it's already crowded there with exhaust plumbing and the raw water pump. Has anyone out there done a second alternator?

On Pete's post, you mentioned that you could tell by the TAC if the belt was slipping, was that because the tac is alternator driven, so if it slips, the rpm shown doesn't rise like you hear from listening to the engine?  I could tell by smell and squeal, I was too distracted to pay attention to the TAC. It could have been slipping a bit at lower RPM, I just didn't notice.   (We're still figuring this out, sorry if that's an obvious question).