On board charger putting out 10 volts DC

I bought a new to me boat recently. Today I hooked up electricity to the boat in my yard and checked the battery charger. It is getting 120 volts ac and it is putting out 10 volts DC to the batteries. Is this normal or should it be putting out more? It is not a smart charger. It is original to the boat. It is a 1995 readi-amp 15 battery charger.

Re: On board charger putting out 10 volts DC

That depends on what the battery voltage is. if you are getting 10v at the battery with the charger turned on then turn it off and i bet you will be getting 10v or less indicating a bad battery or one thats very flat and proberly will not charge

Re: On board charger putting out 10 volts DC

It should be reading 13-14 volts. Bad battery or bad charger.

Re: On board charger putting out 10 volts DC

The voltage at the DC side of the charger was 10 volts I have not checked the voltage at the battery yet. I know it is low because it won't turn the starter.

Re: On board charger putting out 10 volts DC

This is an old school, low budget charger. A Transformer, a Rectifier, and a Meter if you're lucky.

The output may be rectified, but Unfiltered DC. Essentially a bunch of DC pulses.
The meter will try to report the RMS voltage as best as it can figure it.
The peak voltage may very well be near 15-16 volts and the battery will charge fine. :joyous:

What is the voltage on the battery with the charger attached?
If it goes above 14 volts after a short period, The charger is charging.

Re: On board charger putting out 10 volts DC

Ok.
Here is an update. I checked the battery it has 10.2 volts. The charger is receiving 120 volts ac and putting out 10 DC. I put an extension cord to a 30 amp locking shore power adapter. I verified the charger is receiving 120 volts through the distribution panel. I left the charger on overnight. When I checked the battery this morning it was still at 10 volts DC. So I rechecked the charger and found out it was not getting 120 volts ac anymore. I worked backwards and found out the gfi outlet on the outside of my house that the boat was plugged into had tripped.i reset the gfi and confirmed I had 120 to the boat again. All tests for voltage were done at the source, meaning battery voltages were tested at the posts charger in and out voltages were done at the bottom of the charger with a working volt meter. So I was not depending on a gauge. What I really need to know is what voltage would these older style charger put out in DC ? It is still putting out 10 volts DC. Is this normal or should it be putting out 12-14 volts DC?

Re: On board charger putting out 10 volts DC

It is not normal if you measure the voltage of the charger with no load and its 10V.

Re: On board charger putting out 10 volts DC

If you are not seeing above 12.6 volts at the battery either the battery is not accepting a charge or the charger is not working. So again, have the battery load tested. Or substitute a known good battery and see what happens. If voltage is still low, you have a bad charger. A battery cannot be fully charged if charge voltage only goes to 10.2 volts. A fully charged battery measure 12.6 volts after a charger is removed and the battery is allowed to stabilize for a few minutes.

Re: On board charger putting out 10 volts DC

I bought a dual purpose battery last night figuring I would have to replace at least one of the two batteries. I will hook it up today. So if I read correctly you think if I hook the charger to a new battery the output voltage on the charger will go up? That makes no sense to me.

Re: On board charger putting out 10 volts DC

Do yourself a big favor and buy a new 3 stage charger. Your batteries will last longer using a charger like that anyway.

Re: On board charger putting out 10 volts DC

There are three voltage measurements you need to do to figure out what your problems are. The first is the output of your battery charger without connecting it up to the battery yet. It is called open circuit voltage. If that voltage is not more than 13 volts or more, then your changer is bad. The second is the battery voltage without the charger connected up. If your voltage is around 10 volts, you may also have a bad battery as well. And finally the voltage at the battery with the charger connected up and charging the battery. If this voltage in not higher than the battery voltage you previously read, it is never going to charge your battery ever. So unless you know electronics and like repairing battery chargers, just go buy a new modern self monitoring/shut off charger and maybe even a new battery and problems will be solved... You can't charge any battery with a lower voltage then the battery and you can't make a bad battery come back to life either.

Re: On board charger putting out 10 volts DC

Buying a new charger is definitely going to happen. Just not sure when yet. Trying to figure out if I can save this charger for at least a season.

Re: On board charger putting out 10 volts DC

Gm280,
Thank you. That is exactly what I needed. I will check the charger output voltage without a battery hooked up to it. I am 99% sure the batteries are toast. I was just trying to figure out how to test the charger. Thank you to everyone who responded.


My biggest problem is wording the problem I actually want the answer to.

Re: On board charger putting out 10 volts DC

When measuring the voltage of a 12-Volt battery, you need to measure the voltage to at least 0.1-Volt resolution in order to provide useful information, that is, information that has diagnostic value. The Voltmeter should have an accuracy of at least 0.5-percent. At 12-Volts, 0.5-percent is a variation of [0.06-Volts].

A "12-Volt" battery that is completely discharged will have a terminal voltage of 10.5-Volts. All voltages related to state of charge are subject to some variation for temperature. The voltages I mention are for nominal temperature, say 70-degree-F.

To charge a 12-Volt lead-acid battery you must connect a source of current to its terminals with a source voltage that is greater than the terminal voltage of the battery. When you do this, current flows from the charger into the battery, where it can be stored.

To fully charge a 12-Volt battery you must raise the terminal voltage above 12.9-Volts. A typical 12-Volt battery charger will raise the terminal voltage of a 12-Volt battery at full-charge to around 14.4-Volts. After the charger is disconnected, the battery terminal voltage will drop, and the charge will dissipate until the resting voltage of a fully-charged battery is around 12.9-Volts.

A charger that has only limited current available that is connected to deeply discharged battery whose terminal voltage is 10.5-Volts may not have enough capacity to pull the terminal voltage up very much. It may only pull up the terminal voltage slightly. However, if you leave the charger connected and let it build charge in the battery over many hours, the terminal voltage will slowly rise, reaching 12.9-Volts or more. It is probably prudent to slowly charge a battery that is completely discharged than to try to push 100-Amperes into the battery in a few minutes.

Having worked with battery powered equipment all my life and been responsible for the repair and maintenance of battery-powered equipment, I have developed a simple rule to use when diagnosing problems in the operation of battery-operated equipment:

If a battery-operated device appears to malfunction, the first component to test is the battery.

Lead-acid storage batteries that are allowed to sit for long periods at deep discharge states are often damaged beyond recovery. The storage of electricity in the battery is a chemical reaction that is reversible. However, if allowed to sit in a dormant state with a deep discharge, the chemistry can often not be restored, and the battery becomes permanently damaged.

If you need a battery to start your boat's engine, it is reckless to not have a reliable battery. Most boaters whose boat engine cannot be started without a battery usually carry two batteries on board to ensure good engine starting.

Re: On board charger putting out 10 volts DC

.5% of 12V is .06V. Did you mean 5%?

Re: On board charger putting out 10 volts DC

NYBo said:

.5% of 12V is .06V. Did you mean 5%?

Click to expand...

Yes, slipped a digit there. I corrected it.