Power for ER blowers

[TorronaPwr]

I have three blowers clearing any gas fumes from the ER, presently powered by the SB starter battery, and dropping voltage to around 11 when in use. I'm wondering if anyone prefers to have these connected to the house battery instead? What are the pros and cons?

 

[kchace]

IMO the blowers should absolutely be connected to the house bank. The only loads on engine batteries should be the engines.

Ken

 

[rslifkin]

I agree, put them on the house bank. Anything that isn't powered through the engine key switches shouldn't be on the start batteries. Basically, it should be impossible to accidentally drain the start batteries.

 

[TorronaPwr]

Thx guys, I thought it might make more sense to use the house battery, but it was wired this way when I bought the boat used and wasn't sure if had come from the factory that way. Cheers!

 

[DavidM]

Three blowers is quite a lot. Why three?

Also the voltage dropping to 11 is a lot. Maybe the wiring is too small or bad connection causing voltage drop. Are you measuring at battery terminals?

David

 

[Comodave]

Agree that the voltage dropping to 11 is not good. Maybe the start batteries are weal or bad connections on the blowers, undersize wire etc.

 

[BruceK]

If the engine(s) are running when the blowers are, and voltage drops to 11 the alternators do not provide the amps being consumed. It should be a simple pass through. Or is this a prestart safety procedure for gas engines? If so a brief period of associated voltage drop might be ok and to be expected. 3 blowers seems a lot, what`s the total amperage draw? If you then start engines and the batteries are quickly recharged, it may not be such an issue but more a reflection of a necessary safety procedure.

 

[Portage_Bay]

I agree, put them on the house bank. Anything that isn't powered through the engine key switches shouldn't be on the start batteries. Basically, it should be impossible to accidentally drain the start batteries.

My lesson learned. On a delivery I turned on the engine room blowers on a hot day. The Cummins electronically controlled engines died a short time later. The blowers were powered from the start bank. Clearly there were other things wrong as well. Still it points to the risks of running any extra loads off the start bank(s).

 

[O C Diver]

Yes I would also recommend the house bank as you might want it on for some minute after the engine shutdown to cool the engine room or when running a generator. If I'm planning on doing some maintenance after cruising for the day, I leave the blower on for a couple of hours before entering to cool the room.

If you have an automatic fire suppression system in the engine room, it's important to have a shutdown system for the blowers, engine, and generator as they will evaluate the fire suppression gas.

Ted

 

[rslifkin]

The start battery driven setup is likely original. A lot of boat builders make poor assumptions about how the boat will be used and skimp on the battery setup as a result. I've seen many boats where the builder put in a minimal battery setup and just assumed that if you weren't on shore power you'd have the generator running 24/7, so nothing would ever draw the batteries down.

Three blowers is quite a lot. Why three?

Three blowers isn't necessarily unusual for a larger gas engined boat. Depending on the size of the blowers used, 3 may be necessary to meet the airflow requirements with a decent size engine room. My boat has 3 as well. They're not huge blowers, but having more blowers also means you can draw air from the places where fumes are most likely to originate. Mine draw from under each engine as well as the bilge space between them, for example.

 

[TorronaPwr]

Yes, mine is the same as yours rslifkin, small blowers, one under each mercruiser and one low in the lowest part of the bilge. I ran the boat for almost a full season before looking under the engine room shelf, and then found the hoses completely useless, fully rotted through........... I usually run the blowers non stop on coastal trips because I kept forgetting to put them on when coming back to the berth. Maybe this is a bad practice? ........ Both starter batteries are new and also load tested well, and I only noticed the voltage drop at the helm voltmeter, and also at the CB panel voltmeters, so should check at the alternators I think. It takes a long time for the voltage to return to normal, maybe an hour after starting a trip, so I will check wiring size and connections. .....O C Diver I do have an ER fire suppression system but didn't really understand re the shut down system...could you explain further?

 

[rslifkin]

If there's a proper shutdown system tied in with the fire suppression and blowers then the blower power should go through a relay on the shutdown system. That way if the fire suppression triggers it cuts the power to the blowers to avoid venting all of the extinguishing agent overboard.

As far as blower use, I run mine before startup but usually shut them off once we've been moving for a few minutes as the engines are pulling air through the engine room and we get a decent bit of natural draft from airflow over the vents on the sides of the boat. I'll sometimes leave them on at slow cruise in hot weather for extra airflow through the engine room. I usually turn them back on for a few minutes after shutdown to help remove some heat and vent any post-shutdown vapors that come off the carbs. When we run the generator, I leave the blowers on the whole time.

 

[TorronaPwr]

Thx for the explanation rslifkin, I appreciate it. Would it be true to say that with EFI there would be little chance of gas vapors once running and on shut down, meaning the only crucial time to run the blowers would be pre-start?

 

[rslifkin]

Yes, with EFI I wouldn't worry about running the blowers after shutdown. Even with carbs I've never seen an engine produce any noticeable fumes in the bilge after shutdown unless something was seriously wrong, but sometimes you'll get a little bit of warm fuel vapor smell rising to the top of the engine room (and often finding its way into the rest of the boat) when things are first shut down hot. I get it sometimes on my boat. Typically can't smell it in the engine room unless you stick your nose right to one of the carbs, but it's noticeable in the salon above if the windows aren't open. Running the blowers for a few minutes after shutdown pulls it right out of the boat and solves the problem.

 

[TorronaPwr]

Thx for the info - this is a great place to get help