Highest Volatge advisable

Hi Gonzo, have done that many times to see whether the battery of my universal meter still had enough juice in it. I don't think I will be licking the battery terminals in the boat, but it will be realistic, if I have collected water in the boat, for whatever reason. Therefore I need to know my limits. Standing barefeet with wet hands is a reasonablr senario and that I will test out. Bert

 

Absolute correct. I will do so.

 

Well, I quickly got 5 liter seawater from the sea and did some primitive measurement. Noway will I go over the 24 (28.8) Volt.
a) First I measured with my universal Major MT24 on the Ohm setting the resistance of the seawater at 1 cm apart and 30 cm apart. I did not trusted the reading. 14,5 - 15,5 KiloOhm. Although it is a reasonble expensive meter, most likely the voltage used is not high.
b) I stood in a bucket of seawater and had seawater in the basin. I measured 22,6 KOhm i.e. body resistance about 6 KOhm
c) Then I placed a 12Volt (13.31V) battery in series with the meter and basin and measured the current through the basin. 0,5 Ampere i.e. 24 Ohm
d) Then I took 2 batteries in series i.e. 26,54 Volt with a 1100 Ohm resistance in series with my both hands. i.e. currentflow through my heart. I had a wound in my hand and it was not a pleasant feeling. total current 3.2 mA i.e. if my body was zero, the current would have been approx 22 mA. But a resistance of 6 - 8 KOhm is normal for me in wet condition and the current measured is prickling, but acceptable.
My conclusion I will not go over the 24 Volt (30 Volt). Maybe when I am able to figure out on how I can seal "for ever" all the connections, I may go to 36 Volt (40 Volt)., But for the time being 24 Volt is my limit.
Thanks for all the help given.
Bert

 

One thing I have done for years;
I run electrical via ceiling and plumbing via bilge.
It keeps electrical dry, and running as long as possible in sinking emergency. The power to the bilge pumps goes straight done and is sealed three feet above floor of cabin.
The plumbing will always break at some point, so put it where it will do less damage.

This is common sense afterall but I have seem many boats with all electrical in Bilge and some with plumbing all over walls and ceiling.

Batteries are also kept a little higher than bilge, so they can power pumps longer.

 

That make sense. But I have a small problem. I need to keep the weight as low as possible and that makes it very difficult. In your case you have a heavy engine which is placed low. I need to compensate for that low positioned weight with the weight of batteries. All what I can think of, is the suggestion by one of the forum members to mount the batteries in a watertight casing. Not easy in practical terms, if you need to get at least 10 KWh, but preferable 24 KWh. I have bend many hours over the drawings I made, to see how to do it, also when driving long distances, my mind scroll over every detail. I did found a product called "Star-Brite" but have not been able to test it to the bone. The problem with AGM sealed batteries, they still have a vent. The Lithium batteries are fine. They can be sealed in a pipe or sleeving system, as long I charge with low currents and no heat is generated.
Bert

 

I said not in bilge, not to raise batteries above eye level. Depending on boat design, batteries can usually be placed just above waterline without affecting center of gravity too much.

 

...when I hear "electric boat" I think of electric stove,fridge,anchor winch, thrusters, etc.

If it's for propulsion then the higher the better...

 

That is my concern, I will have in excess of 180 kg/400 pounds of batteries.
I am able to do the calculations for stability. But never the less, I cannot go too high, I need to keep it as low as human possible.

 

I don't know whether I like to have 48 Volt. If I ever go for a higher voltage than 24 Volt for the propulsion, I will first convert it into 50 or 60 Hz and the at the higher Voltage just convert it back to DC and then feed it into a potted controller for the brusless motor.
Bert

 

High voltage also starts the heart too, bit ironic to use electricity to start what stopped it in the first place.

 

Very true, the difference offcourse is, the unit which start the heart again, is a one off pulse. I wonder how high the voltage actual is, for a heart recovery machine. 100 KVolt? 10 KVolt? I have no idea.
What would happen to our hearts at 1000Hz or 10 Khz with let say 150 Volt.
Would the body be able to dislodge from the terminal if accidenmtal touched? I have quite a number of times acidental touched the 220 Volt AC. Due to the fact it is only 50HZ, with the shock, my hands got free.

The reason why I ask, otherwise I could convert 24 Volt with a inverter close to the batteries and even enclose it waterproof with the batteries and then at 10 KHz pump it up to 150 Volt and convert it to DC. Use thinner cables and use normal cable glands. Build a controller with high voltage N or P type MOSFets (The controller will be below waterline with the motor and AC to DC converter). De controllers I have build now, is maximum 55 Volt, 200 Ampere.
Bert

 

Put it in a water tight box vented above.

 

Capacitor discharge, 1000 VDC, in steps of 50 KJoules to a maximum of 200 KJ for adults. The defibrillator can go further, but if a 200 KJ shock doesn't produce a heartbeat the patient is pronounced dead (except in Hollywood of course).

 

That is an idea. I can put it right under in the boat in a sealed box, of which the lid can be removed for maintenance, with pipes going up for ventilation. I can in principle make the pipes as high as whatever is practicle.
Excellent idea. Thank you.
Bert

 

Thanks CDK. I knew that it had to be a capacitor discharge, but had absolute no idea how high the voltage was.
Thanks.