Thread: New Helix units and power.

Originally Posted by N2Crappie

Alphahawk

My HB units have always read about a half volt to one volt lower than the actual voltage.

That is not avoidable. The current being drawn by the unit causes a voltage drop in the wires feeding it. The unit is seeing about a volt less than the battery is supplying because of this loss and that's what it displays.

A couple of things follow from this that may interest you. Since the voltage drop is caused by current and the resistance of the wire, if you reduce the current, you'll reduce the drop. You can demonstrate this by changing the backlight brightness on your unit and watching the voltage. With the backlight way down, the voltage reading on the unit will be closer to the actual voltage.

The other interesting thing is that this explains why larger wires are used for applications where you need high current. Your TM wiring may need to handle more than 50A. Heat aside, if you used 18AWG wire to run a 24V TM, you'd get about 10V to your TM. By stepping up to 6AWG, you'd get 24.42V out of the 25.3V your batteries provide. Stepping up to 2AWG would get you 24.97V.

Additionally, every connection in a wire makes the issue worse. Fuse holders, splices, connectors etc. all add loss. Shorter, heavier wires do a better job of providing power to equipment. The voltage that is "lost" in wiring and connections is actually wasted as heat.

They have a polarity protection diode to keep from being hooked up backwards & fried, and the rectifier drops your forward voltage about 8/10th volt.

When testing a battery a great tool is a hydrometer. Inexpensive but actually does a better job than most " battery testers " at many auto parts stores. It performs specific gravity test. Which is high falutin talk for how much acid is in the battery fluid. Any reading in the green zone indicates a good battery. Each cell must be measured as one "dead " cell will cause problems. Dead cells give a yellow or red zone reading. This test can be performed with battery still installed in boat. Just ensure that nothing is running off the battery.

Uncharged batteries will reflect " bad readings ". So best time to test with hydrometer is right after full charge cycle has been performed on battery in question.