Riser Repair

Can you convert your commutator from inserted to solid risers?


A solid riser commutator is one in which the riser, into which the coils are inserted, is made of the same piece of copper as the rest of the bar. In a solid riser v-ring commutator, a rectangular shaped bar of copper has the three sections machined away - at each end for the dovetail,
and along the brush track, leaving the riser.

If a riser is very long, a tremendous amount of copper would be wasted to leave the riser. Instead, an inserted riser design was developed.

Winders, however, often prefer to work with solid riser designs, so how can you tell if your commutator is a candidate for conversion?

Alloy 116 (silver bearing commutator copper) is typically readily available in sizes up to 4, or even 5, inches in width. If your commutator from the inside diameter of the copper to the outside diameter of the risers fits within this, conversion may be a viable option.

What if the bar needs to be wider than available copper sizes?
An alternative to a solid riser is a lap joint design. A separate riser is brazed to the copper bar, but shaped to match the trapezoid of the bar itself. Though typically more expensive than an inserted riser unit, a lap joint riser will provide all the benefits of a solid riser commutator, i.e. carbon contamination prevention behind the risers.

What should you consider in a conversion?
If the risers in question are quite long, you will be adding weight to the unit, potentially
affecting performance. In addition, if cooling and airflow are considerations for your
application, note that the solid risers or lap joint will cut off this air flow versus the inserted riser design.
Call your ICC sales representative to discuss the possibility of conversion of any
commutator you have in house.

Options for repairing broken commutator risers

If the risers are broken at the brush track or only slightly beyond, your options are severely limited.


Inserting new risers is not a viable option, since the heat required to braze the new riser in place would quickly burn and destroy the segment mica between the bars. Soldering is also not recommended, due to the likelihood of contamination of the segment insulation. In addition, solder will rarely withstand the operating temperature requirements of the unit.

T.I.G. welding extensions is not an option due to the small amount of riser material remaining attached to the comm. In this situation, there are typically two possible options remaining for repairing the problem:

Refilling the commutator - involves reusing the steel core, but manufacturing new copper, risers, and insulation. Reinsulating the commutator - involves reusing the steel core, and the copper bars (on large units), replacing the risers and insulation. Note: reinsulation is not typically an option for glassband commutators, which we will address in a future issue of Motor Fax.

If the break is further along the riser, the repair is much less complicated.

T.I.G. welding extensions is a good solution to this problem, assuming that the commutator is otherwise in good condition and that there is still substantial brush life left on the unit. To effectively perform this repair, the risers need to be thoroughly cleaned, removing all carbon contamination.

New risers should be fabricated from the same material used in the original unit. This is typically half hard, oxygen-free copper, in thicknesses ranging from 0.020" to 0.125". Riser extensions should be bent prior to installation, allowing 0.002" in width and 0.312" in depth greater than coil sizes for easy coil installation.

For recurring problems with cracked risers due to vibration, you may want to consider adding a row of lashing to help minimize this effect.

Shown below are some of the more common riser styles, to help in your identification.