Voltage drop on starting

[wrapper]

I have two reasonably good batteries with an A-All-B switch.

I am still getting big voltage drops each time I start then engine. The instruments reset and the VHF resets back to 16.

I rewired almost everything in the primary starting circuit and put the grounds of the batteries together to minimize voltage drops.

I am suspecting the starter might be getting old or just has such a large drain that my electrical system voltage drops.

Someone recommended I try a battery isolator to prevent the voltage drop on my electrical system. This makes sense.

Are there any other suggestions ?

[tenders]

This happens because your voltage drops below the threshold at which your VHF can keep its mojo. A larger-than-designed starter drain could be the problem...but more likely your batteries are a little old, or too small, or not completely charged.

For example, maybe your boat had an A4 and it's been refitted with a diesel. Diesels use more juice to start. If the batteries weren't also upsized, you may not have enough juice to keep everything copasetic while you're cranking. One way to tell--try jumpstarting your boat from your car while it's on the hard, or use a self-contained booster kit. This adds cranking capacity, usually at close to full voltage. Do the instruments reset?

A battery isolator is basically just a capacitor, which stores a small charge for a short amount of time close to components with a small current drain, plus a diode which prevents that charge from leaking out to the starter for a few instants while the starter is engaged. They aren't a perfect solution -- the diode creates a slight voltage drop in the system so your radio won't operate at peak efficiency.

[MikeB.330]

you should also consider having a dedicated starting battery so that starting the engine will not pull down the house bank. In turn if you run down your house bank you will still be able to start the engine. An A4 really doesn't pull that much juice so you may want to check your batteries as well.


Mike

[marthur]

MikeB,

I have seen a similar thing happen with my A-4. However, it happens when the battery is low.

To prevent this when the batteries are low, I will start my engine with the switch on "both" or run the radios on A while starting on B (I have a battery selector switch for charging and on the electrical panel).

Good luck,

Mike A.

[CalebD]

As others have suggested you might want to check the mojo of your battery bank. Do you take the batteries off and keep them trickle charged, warm and cozy during the winter? This is not a particularly fun job unless you enjoy lifting weights but has helped us to get multiple seasons out of the same batteries. We also installed a solar trickle charger for when the boat is in the water.
Why do you need to keep the VHF on when starting up the engine anyway? Wouldn't it be easier to just start up the engine and then turn on the radio and blower? If your batteries are weak to begin with why add unneccesary load to them while they are trying to startup your engine.
On our boat the VHF is hard wired right to one battery so that it can be used at the flip of the power switch on the radio without having to turn on any breaker or battery selector switches (in line fuse of course). I believe that this is a safety feature if the radio is needed in a hurry. Even so, we hardly ever start the engine with the radio (or other gizmos) turned on.
Good luck.

[bayareadave]

Keep in mind toasted batteries may show a normal voltage at rest, but die when put to load. If you have someone to help you, you can use a voltage tester to try and find out where the load is happening - there are some other posts that talk about that. Also, feel the wires, switch, and connections after trying to start - any parts warm? If so, that would indicate an area of high resistance.

You didn't say when the probems started, but if your batteries are located such that there is a long run of wire to the switch, then to the starter, you could lose a lot of power to resistance.

As for the battery isolator, I don't get how that would help. My understanding is those allow both batteries to receive flow from a source (charge), but prevent flow of voltage from one battery to the other.

[Chip Hindes]

This could be more complicated than you might think.

You don't say where the switch is set when you attempt to start the motor. Normal practice with a off-1-both-2 switch, two deep cycle marine batteries and a big motor is to move the switch to "both". This puts both batteries in parallel, effectively doubling the cranking amps, to give you an extra boost to start the motor.

In truth, our puny little A4s can get all the starting juice they need from a single deep cycle marine battery, so using the both setting should not be necessary except in an emergency and to charge both batteries.

However to your problem: even with a good system and good batteries, my sense is the inrush current on a starter just as the solenoid is closed may still cause enough instantaneous voltage drop in the system to cause your radios, etc to drop out. It only takes an instant, not even long enough that it would register on a conventional multimeter. The voltage comes back up right away or the starter won't crank at all. Voltage drops to the starter circuit which are calculated based on wire size and length are based on steady state. Inrush is different and calculations for starting the motor need not take it into account.

I don't know because I've never tried it, but it's possible that even with two good batteries and the switch on the "both" position, there may be enough instnataneous voltage drop when you close the starter switch to drop out your radio. BTW, subjecting the radios etcetera to this when you crank the motor can't be good for them.

The above and your original problem point out one of the major drawbacks of the off-1-both-2 switch. Except in the both position, only one battery is in use at any one time for both motor and house loads. With the switch in the both position, you have the power of both batteries but have defeated one of the benefits of the system, in that instead of always having one fresh battery to start the motor, you could inadvertantly kill both batteries with your house loads.

I have two completely independent electrical systems and a three switch control. My house and motor systems each have their own battery and are not connected together except in an emergency (and by a separate electronic relay for charging). The only thing on the my motor side electrical system is the motor. My instruments are all on the house system, not the motor system, so they are completely unaffected by the starter loads.

In an emergency if the starter battery were to die, the third switch parallels the system to start the motor.

bayareadave is right. An isolator can have no effect on your problem. It doesn't isloate the loads from the battery; in a multi battery system it isloates one battery from the other so they can be charged by a single charging source while not connected together.

[Bob N]

Can't comment on the specifics of your situation, but I always make sure that my radio and depthsounder are off at the fuse panel before starting (and if I had other electronics they would be switched off as well). Who knows what sorts of drain--or spikes--could be pulsing through the system when you crank up the starter?

[SFBayLarry]

I'm having a similar starting issue, which is making starting difficult. After making sure cable connections were good, batteries charged up (3 years old), and having the starter rebuilt, I am still having a hard time getting it started.

It seems to only want to fire up just as I turn the ignition switch back from "start" to "run". Sorta like the starter is using all the current, and the plugs aren't sparking until I switch back to run. Once started, the engine runs fine.

I monitored the ignition voltage at the starter switch, and I'd see it drop from 13v. to about 5v. when the starter is being used. How many volts are needed to create spark?

Might I have batteries that are over the hill, or should I look somewhere else for this current loss?

Larry

[rigspelt]

Originally Posted by SFBayLarry

I'm having a similar starting issue, which is making starting difficult. After making sure cable connections were good, batteries charged up (3 years old), and having the starter rebuilt, I am still having a hard time getting it started. It seems to only want to fire up just as I turn the ignition switch back from "start" to "run". Sorta like the starter is using all the current, and the plugs aren't sparking until I switch back to run. Once started, the engine runs fine. I monitored the ignition voltage at the starter switch, and I'd see it drop from 13v. to about 5v. when the starter is being used. How many volts are needed to create spark?

Couple of thoughts from my amateur perspective:
1. Engine start battery voltage can drop to the 10's briefly during cranking, and should bounce immediately back to about 12.6 after cranking. If your battery voltages really are dropping to 5 (measure them at the battery), then I might suspect one of the batteries. Well maintained batteries should last at least 3 seasons, but that requires meticulous attention, and some cheaper lead acid batteries might fail at 3 years, judging by what I've been seeing on the docks.
2. But I wonder if there is a wiring problem at the ignition switch, or whether the switch itself is faulty? Set to "run", the starter solenoid should not be getting electricity, so the starter should not crank. I might have a good look at the ignition panel, and even consider swapping in a new ignition switch, since that's a cheap step and I gather failed ignition switches are not uncommon?

[67c&ccorv]

[QUOTE=wrapper;6381]

I rewired almost everything in the primary starting circuit and put the grounds of the batteries together to minimize voltage drops.

Start here.

Someone recommended I try a battery isolator to prevent the voltage drop on my electrical system. This makes sense.

A battery isolater prevents a higher charged battery from discharging into a lower charged battery resulting in two undercharged batteries.

It also reduces the charging current from the alternator by .6 volts - which if left unaddressed will also result in two perenially undercharged batteries.

Are there any other suggestions ?[/QUOTE]

No.

[smosher]

Make sure the ground attachment is to the motor and attached with at least a 4 awg wire to a clean surface. Typically voltage drops are caused by the ground.

I had the same trouble and replaced all of my primary wire with new 4 gauge and fixed my voltage problems.

Steve

[msauntry]

My engine was getting harder and harder to start. It got so bad I started popping the main fuse and would have everything go out until I could pop in another one. Turns out my starter needed rebuilding and once I had that done, no more problems.

If your batteries are otherwise behaving normally, I'd look to the starter.