Minimum battery capacity for 50TLDI

[nevd]

I would appreciate the experience of others who have tried to install small batteries on Tohatsu 50 tldi motors. The engine will start reliably with a 25AH, 275CCA battery except the memory keeps logging low battery voltage fault codes in memory. Sometimes at idle, if the power trim is actuated, the engine will miss presumably because the alternator is not charging and this causes battery voltage to get lower than the engine management system needs to run reliably. It is suspected this is what causes the fault logging.<br /><br />Local dealer says motor needs a very large 100 AH battery to run reliably, but the 20kg weight increase to go from 25 to 100 AH will cause problems with boat balance. The big benefit of the 50tldi compared with all other low emission 50 hp engines is the Tohatsu has the best power to weight ratio and the large battery will remove this benefit.<br /><br />Does anybody know voltage which triggers a low battery log? The experiences and advice of readers would be appreciated.

 

[ziemann]

Re: Minimum battery capacity for 50TLDI

You will need a minimum 100AH (or 120AH in cold climates). You will log a fault when the voltage drops below 10 volts. The current battery you are using is inadequate.

 

[khc1970]

Re: Minimum battery capacity for 50TLDI

Surely a 100ah battery doesn't weigh 20kg than a 25ah?

 

[nevd]

Re: Minimum battery capacity for 50TLDI

A 100 A/H battery is quite large and is between 23 and 30 kg more (depends on manufacturer) than the 25 A/H battery which would easily start the 50 HP motor. After extensive use of power trim and while power trim motor was stalled out, the minimum voltage at the motor was 12 volts, but it was noted that voltage dropped much lower when starter motor was engaged.<br /><br />Since motor starts so quickly, we will need more time to get accurate results of voltage at outboard during starting conditions to determine if voltage drops below 10V nominated by Z-Man MT. We will post results when available.

 

[khc1970]

Re: Minimum battery capacity for 50TLDI

Can you not connect up 2 x 25 and stick one battery on either side of the boat for balance?

 

[nevd]

Re: Minimum battery capacity for 50TLDI

We now have the additional test information on 50 TLDI battery voltages while starter motor is engaged.<br />Voltage across starter motor is normally 10.1V but can drop to 9.8 if motor cranked over for approx 5 secs or more.<br />No load battery voltage 12.6V, but drops to 10.5V when starter motor voltage drops to 9.8V.<br />Total voltage drop in battery leads (which have been shortened to 1/2 of original length) is .7V.<br />The low voltage warning light is supposed to alarm when voltage across motor drops to 10V and during extended cranking of motor, the warning light normally shows for a very brief period (confirming voltage has dropped below 10V).<br />We can therefore conclude that internal resistance of the battery causes a voltage drop due to starting currents of 2.1V and shortened battery leads causes a further voltage drop of .7V. <br />To stop undervoltage alarms and fault codes, internal resistance of battery will need to decrease to allow say .5V more at the motor.<br />Assuming internal resistance is approximately proportional to Cold Cranking Amps (CCA), then new battery CCA = old battery CCA*2.1V/(2.1V-0.5V) =275*2.1/1.6 =361<br /> <br />We therefore need to replace the battery with a larger battery giving CCA of 361 or greater or connect up a second battery in parallel as suggested by khc1970. Can anybody see any errors in this analysis or offer alternative recommendations to stop the fault codes refered to in my June 11 message?

 

[TOHATSU GURU]

Re: Minimum battery capacity for 50TLDI

Or you could just follow the manufacturers specifications as to the size of battery that is required and ....

 

[nevd]

Re: Minimum battery capacity for 50TLDI

Elvin,<br /><br />The lightest 100AH battery I have found is 32 kg and the outboard is only 3 times as heavy at 96 kg. Can you recommend a lighter battery which meets manufacturers spec?<br /><br />Thanks,<br /><br />nevd

 

[khc1970]

Re: Minimum battery capacity for 50TLDI

I have a 90 tldi with a twin battery set up, one is 80ah and the other 100ah. The outboard starts without any problems on either battery. Not sure how much they weigh, will have a long tomorrow.

 

[whoopy]

Re: Minimum battery capacity for 50TLDI

For what its worth. I carry a garden tractor size Everstart deep cycle battery, left over from a previous boat, as a backup. Very light and can be easily moved to and from the boat. I have only used it twice to make sure it worked and it did. On the label all it says is 34 amp hrs. <br /><br />Unfortunately I have a problem with all three warning lights coming on that I will be posting separately. Hope it wasn't related to using the small battery.

 

[nevd]

Re: Minimum battery capacity for 50TLDI

50 TLDI has now been fitted with the larger 35 A/H battery and motor does not show the low voltage warning light on start up ever. So with the shortened battery leads, it looks like the 35A/H battery is adequate.<br /><br />Sometimes at 700RPM idle (not at 800 or 900), it will still stall when the power trim is acuated - low voltage light does not come on. Does anybody have any suggestions on why the stalling?

 

[TOHATSU GURU]

Re: Minimum battery capacity for 50TLDI

Low voltage because you are using battery that is too small and the engine charging system is not producing enough amps at that RPM to make up for it.

 

[ziemann]

Re: Minimum battery capacity for 50TLDI

*bangs head on desk*

 

[TOHATSU GURU]

Re: Minimum battery capacity for 50TLDI

But not too hard...it hurts too much.

 

[nevd]

Re: Minimum battery capacity for 50TLDI

As stated in my 15/6 posting, minimum voltage across motor was 12V at idle even following extensive use of power trim. It was under these conditions which occasionally would see the motor stall at 700 RPM idle. <br /><br />Are you Elvin and Z both saying the motor will stall if battery voltage is not consistently held above 12V at the motor (and not the 10 V which causes the undervoltage light to glow and the motor to fault code) and this is why Tohatsu wants a 32kg to 40 kg battery fitted to a 96kg outboard motor?

 

[TOHATSU GURU]

Re: Minimum battery capacity for 50TLDI

Stop measuring the voltage and just accept that if you do not have at least the minimum size battery the engine will not run correctly.

 

[ziemann]

Re: Minimum battery capacity for 50TLDI

Nevd-<br /><br />You came here asking for advice. We give it to you based upon info from Tohatsu service. You don't follow the recommendations of Tohatsu, then whine that performance doesn't meet your expectations. Have I pretty much summed it up?<br /><br />If you didn't want to hear the answer, why did you ask? Elvin is right on target here...

 

[Dave Wright]

Re: Minimum battery capacity for 50TLDI

I'm very close to buying a Tohatsu 50TLDI. Ny intent is mainly based on having had such excellent performance from an old 40 horse Tohatsu 2 stroke. A friend just mentioned the 100 ah battery requirement, and relayed this discussion to me. I couldn't understand why a 100 ah battery was required for a 50 horse engine.<br /><br />Frankly, I would have missed the requirement, or perhaps the dealer would have pointed it out to me after I had paid for the engine and showed up for installation with less than a 100 ah battery. To me the requirement is not a logical one and I'd love to see a full explanation.<br /><br />To me, nevd's post asking for info on this subject is right on. His attempt to troubleshoot and find some rationale for his engine's performance and relate it to the 100 ah battery requirement is also right on.<br /><br />So I'm surprised and wonder why Elvin and Z-Man MT would simply say this is the way it is,and use the battery specified by the manufacturer. To me, good performance and lightweight is the whole rationale for getting a 50TLDI. How do comments like this help nevd get to the bottom of the situation??<br /><br />Is it fair to ask precisely what are the technical reasons for the 100 ah battery requirement? Further, is it fair to ask why the Tohatsu engineers produced a product with this requirement? Did the requirement "just happen" as a consequence of the normal design flow? Do the Tohatsu engineers consider this battery requirement an "advantage" for either Tohatsu or the customer? <br /><br />As I say, I'm very pleased with my previous experience with Tohatsu, and have touted the product whenever a discussion came up, but lack of satisfactory explanation for this battery issue could make me think twice.<br /><br />Dave Wright

 

[khc1970]

Re: Minimum battery capacity for 50TLDI

Might be it's only me, but I thought Int'board explained it on the 11th reply, quote<br />"Low voltage because you are using battery that is too small and the engine charging system is not producing enough amps at that RPM to make up for it."<br />At low rev, the outboard isn't revving hard enough, so not producing enough amp to compensate for the charge being take out, eventually (or rather quickly) the battery gets very low in juice. <br />Imagine you are trying to jump start your mate's car, whose battery is very low, you tried it with the engine off, no good, so you tried it with the engine idling, still struggles, the only thing left to try is rev your engine so that it produce the extra power needed.<br />Maybe it's a design fault overlooked by the engineer or it might be done on purpose so there are plenty of safty margin, or they designed the larger outboard first and couldn't be bothered to redesign the electric. End of the day, neither a 25 nor a 35 will work properly on the 50 tldi, knowing why it doesn't work won't change a thing, it STILL wouldn't work.<br />As I said before, I have the 90 with 85 (I thought it was a 80 but when I checked the other day, it was a 85) and 100a, both battery CAN start the engine without any problems.

 

[Dave Wright]

Re: Minimum battery capacity for 50TLDI

Whatever, all I can get out of those posts is "this is the way it is."<br /><br />I guess you're telling me that your engine will function satisfactorily on an 85 ah battery. That's good information, thank you very much.<br /><br />Whatever, may I ask you if it's possible to pull start your Tohatsu TLDI with a dead battery?(Let's say a battery depleted to the point where it wil not drive the starter motor). I ask, because ability to pull start is a plus to me.<br /><br />As far as specific info, I'm guessing that knowing exactly what the electrical power requirements are for each relevant component of the engine might make trouble shooting easier if problems are ever encountered. That's why I'm curious. <br /><br />I'll write to Tohatsu directly and also take my questions to my local dealer.<br /><br />Thanks, Dave Wright